Describing Databases with MetaData¶

This section discusses the fundamental Table, Column and MetaData objects.

A collection of metadata entities is stored in an object aptly named MetaData:

from sqlalchemy import *

metadata = MetaData()

MetaData is a container object that keeps together many different features of a database (or multiple databases) being described.

To represent a table, use the Table class. Its two primary arguments are the table name, then the MetaData object which it will be associated with. The remaining positional arguments are mostly Column objects describing each column:

user = Table('user', metadata,
    Column('user_id', Integer, primary_key=True),
    Column('user_name', String(16), nullable=False),
    Column('email_address', String(60)),
    Column('nickname', String(50), nullable=False)
)

Above, a table called user is described, which contains four columns. The primary key of the table consists of the user_id column. Multiple columns may be assigned the primary_key=True flag which denotes a multi-column primary key, known as a composite primary key.

Note also that each column describes its datatype using objects corresponding to genericized types, such as Integer and String. SQLAlchemy features dozens of types of varying levels of specificity as well as the ability to create custom types. Documentation on the type system can be found at Column and Data Types.

Accessing Tables and Columns¶

The MetaData object contains all of the schema constructs we’ve associated with it. It supports a few methods of accessing these table objects, such as the sorted_tables accessor which returns a list of each Table object in order of foreign key dependency (that is, each table is preceded by all tables which it references):

>>> for t in metadata.sorted_tables:
...    print(t.name)
user
user_preference
invoice
invoice_item

In most cases, individual Table objects have been explicitly declared, and these objects are typically accessed directly as module-level variables in an application. Once a Table has been defined, it has a full set of accessors which allow inspection of its properties. Given the following Table definition:

employees = Table('employees', metadata,
    Column('employee_id', Integer, primary_key=True),
    Column('employee_name', String(60), nullable=False),
    Column('employee_dept', Integer, ForeignKey("departments.department_id"))
)

Note the ForeignKey object used in this table - this construct defines a reference to a remote table, and is fully described in Defining Foreign Keys. Methods of accessing information about this table include:

# access the column "EMPLOYEE_ID":
employees.columns.employee_id

# or just
employees.c.employee_id

# via string
employees.c['employee_id']

# iterate through all columns
for c in employees.c:
    print(c)

# get the table's primary key columns
for primary_key in employees.primary_key:
    print(primary_key)

# get the table's foreign key objects:
for fkey in employees.foreign_keys:
    print(fkey)

# access the table's MetaData:
employees.metadata

# access the table's bound Engine or Connection, if its MetaData is bound:
employees.bind

# access a column's name, type, nullable, primary key, foreign key
employees.c.employee_id.name
employees.c.employee_id.type
employees.c.employee_id.nullable
employees.c.employee_id.primary_key
employees.c.employee_dept.foreign_keys

# get the "key" of a column, which defaults to its name, but can
# be any user-defined string:
employees.c.employee_name.key

# access a column's table:
employees.c.employee_id.table is employees

# get the table related by a foreign key
list(employees.c.employee_dept.foreign_keys)[0].column.table

Creating and Dropping Database Tables¶

Once you’ve defined some Table objects, assuming you’re working with a brand new database one thing you might want to do is issue CREATE statements for those tables and their related constructs (as an aside, it’s also quite possible that you don’t want to do this, if you already have some preferred methodology such as tools included with your database or an existing scripting system - if that’s the case, feel free to skip this section - SQLAlchemy has no requirement that it be used to create your tables).

The usual way to issue CREATE is to use create_all() on the MetaData object. This method will issue queries that first check for the existence of each individual table, and if not found will issue the CREATE statements:

engine=create_engine('sqlite:///:memory:')metadata=MetaData()user=Table('user',metadata,Column('user_id',Integer,primary_key=True),Column('user_name',String(16),nullable=False),Column('email_address',String(60),key='email'),Column('nickname',String(50),nullable=False))user_prefs=Table('user_prefs',metadata,Column('pref_id',Integer,primary_key=True),Column('user_id',Integer,ForeignKey("user.user_id"),nullable=False),Column('pref_name',String(40),nullable=False),Column('pref_value',String(100)))sqlmetadata.create_all(engine)PRAGMA table_info(user){}
CREATE TABLE user(
        user_id INTEGER NOT NULL PRIMARY KEY,
        user_name VARCHAR(16) NOT NULL,
        email_address VARCHAR(60),
        nickname VARCHAR(50) NOT NULL
)
PRAGMA table_info(user_prefs){}
CREATE TABLE user_prefs(
        pref_id INTEGER NOT NULL PRIMARY KEY,
        user_id INTEGER NOT NULL REFERENCES user(user_id),
        pref_name VARCHAR(40) NOT NULL,
        pref_value VARCHAR(100)
)

create_all() creates foreign key constraints between tables usually inline with the table definition itself, and for this reason it also generates the tables in order of their dependency. There are options to change this behavior such that ALTER TABLE is used instead.

Dropping all tables is similarly achieved using the drop_all() method. This method does the exact opposite of create_all() - the presence of each table is checked first, and tables are dropped in reverse order of dependency.

Creating and dropping individual tables can be done via the create() and drop() methods of Table. These methods by default issue the CREATE or DROP regardless of the table being present:

engine=create_engine('sqlite:///:memory:')meta=MetaData()employees=Table('employees',meta,Column('employee_id',Integer,primary_key=True),Column('employee_name',String(60),nullable=False,key='name'),Column('employee_dept',Integer,ForeignKey("departments.department_id")))sqlemployees.create(engine)CREATE TABLE employees(
employee_id SERIAL NOT NULL PRIMARY KEY,
employee_name VARCHAR(60) NOT NULL,
employee_dept INTEGER REFERENCES departments(department_id)
)
{}

drop() method:

sqlemployees.drop(engine)DROP TABLE employees
{}

To enable the “check first for the table existing” logic, add the checkfirst=True argument to create() or drop():

employees.create(engine, checkfirst=True)
employees.drop(engine, checkfirst=False)

Altering Schemas through Migrations¶

While SQLAlchemy directly supports emitting CREATE and DROP statements for schema constructs, the ability to alter those constructs, usually via the ALTER statement as well as other database-specific constructs, is outside of the scope of SQLAlchemy itself. While it’s easy enough to emit ALTER statements and similar by hand, such as by passing a string to Connection.execute() or by using the DDL construct, it’s a common practice to automate the maintenance of database schemas in relation to application code using schema migration tools.

There are two major migration tools available for SQLAlchemy:

Alembic - Written by the author of SQLAlchemy, Alembic features a highly customizable environment and a minimalistic usage pattern, supporting such features as transactional DDL, automatic generation of “candidate” migrations, an “offline” mode which generates SQL scripts, and support for branch resolution.
SQLAlchemy-Migrate - The original migration tool for SQLAlchemy, SQLAlchemy-Migrate is still used by projects such as Openstack, however is being superseded by Alembic.

Specifying the Schema Name¶

Some databases support the concept of multiple schemas. A Table can reference this by specifying the schema keyword argument:

financial_info = Table('financial_info', meta,
    Column('id', Integer, primary_key=True),
    Column('value', String(100), nullable=False),
    schema='remote_banks'
)

Within the MetaData collection, this table will be identified by the combination of financial_info and remote_banks. If another table called financial_info is referenced without the remote_banks schema, it will refer to a different Table. ForeignKey objects can specify references to columns in this table using the form remote_banks.financial_info.id.

The schema argument should be used for any name qualifiers required, including Oracle’s “owner” attribute and similar. It also can accommodate a dotted name for longer schemes:

schema="dbo.scott"

Backend-Specific Options¶

Table supports database-specific options. For example, MySQL has different table backend types, including “MyISAM” and “InnoDB”. This can be expressed with Table using mysql_engine:

addresses = Table('engine_email_addresses', meta,
    Column('address_id', Integer, primary_key=True),
    Column('remote_user_id', Integer, ForeignKey(users.c.user_id)),
    Column('email_address', String(20)),
    mysql_engine='InnoDB'
)

Other backends may support table-level options as well - these would be described in the individual documentation sections for each dialect.

Column, Table, MetaData API¶

Object Name	Description
Column	Represents a column in a database table.
MetaData	A collection of `Table` objects and their associated schema constructs.
SchemaItem	Base class for items that define a database schema.
BLANK_SCHEMA	Symbol indicating that a `Table` or `Sequence` should have ‘None’ for its schema, even if the parent `MetaData` has specified a schema.
Table	Represent a table in a database.
ThreadLocalMetaData	A MetaData variant that presents a different `bind` in every thread.

attribute sqlalchemy.schema.sqlalchemy.schema.sqlalchemy.schema.BLANK_SCHEMA¶: Symbol indicating that a Table or Sequence should have ‘None’ for its schema, even if the parent MetaData has specified a schema.

See also

MetaData.schema

Table.schema

Sequence.schema

New in version 1.0.14.

class sqlalchemy.schema.Column(*args, **kwargs)¶

Represents a column in a database table.

Class signature

class sqlalchemy.schema.Column (sqlalchemy.schema.SchemaItem, sqlalchemy.sql.expression.ColumnClause)

method sqlalchemy.schema.Column.__eq__(other)¶

inherited from the sqlalchemy.sql.operators.ColumnOperators.__eq__ method of ColumnOperators

Implement the == operator.

In a column context, produces the clause a = b. If the target is None, produces a IS NULL.

method sqlalchemy.schema.Column.__init__(*args, **kwargs)¶

Construct a new Column object.

Parameters:

name –
The name of this column as represented in the database. This argument may be the first positional argument, or specified via keyword.

Names which contain no upper case characters will be treated as case insensitive names, and will not be quoted unless they are a reserved word. Names with any number of upper case characters will be quoted and sent exactly. Note that this behavior applies even for databases which standardize upper case names as case insensitive such as Oracle.

The name field may be omitted at construction time and applied later, at any time before the Column is associated with a Table. This is to support convenient usage within the declarative extension.
type_ –
The column’s type, indicated using an instance which subclasses TypeEngine. If no arguments are required for the type, the class of the type can be sent as well, e.g.:
```
# use a type with arguments
Column('data', String(50))

# use no arguments
Column('level', Integer)
```
The type argument may be the second positional argument or specified by keyword.

If the type is None or is omitted, it will first default to the special type NullType. If and when this Column is made to refer to another column using ForeignKey and/or ForeignKeyConstraint, the type of the remote-referenced column will be copied to this column as well, at the moment that the foreign key is resolved against that remote Column object.

Changed in version 0.9.0: Support for propagation of type to a Column from its ForeignKey object has been improved and should be more reliable and timely.
*args – Additional positional arguments include various SchemaItem derived constructs which will be applied as options to the column. These include instances of Constraint, ForeignKey, ColumnDefault, and Sequence. In some cases an equivalent keyword argument is available such as server_default, default and unique.
autoincrement –
Set up “auto increment” semantics for an integer primary key column. The default value is the string "auto" which indicates that a single-column primary key that is of an INTEGER type with no stated client-side or python-side defaults should receive auto increment semantics automatically; all other varieties of primary key columns will not. This includes that DDL such as PostgreSQL SERIAL or MySQL AUTO_INCREMENT will be emitted for this column during a table create, as well as that the column is assumed to generate new integer primary key values when an INSERT statement invokes which will be retrieved by the dialect.

The flag may be set to True to indicate that a column which is part of a composite (e.g. multi-column) primary key should have autoincrement semantics, though note that only one column within a primary key may have this setting. It can also be set to True to indicate autoincrement semantics on a column that has a client-side or server-side default configured, however note that not all dialects can accommodate all styles of default as an “autoincrement”. It can also be set to False on a single-column primary key that has a datatype of INTEGER in order to disable auto increment semantics for that column.

Changed in version 1.1: The autoincrement flag now defaults to "auto" which indicates autoincrement semantics by default for single-column integer primary keys only; for composite (multi-column) primary keys, autoincrement is never implicitly enabled; as always, autoincrement=True will allow for at most one of those columns to be an “autoincrement” column. autoincrement=True may also be set on a Column that has an explicit client-side or server-side default, subject to limitations of the backend database and dialect.

The setting only has an effect for columns which are:
- Integer derived (i.e. INT, SMALLINT, BIGINT).
- Part of the primary key
- Not referring to another column via ForeignKey, unless the value is specified as 'ignore_fk':
```
# turn on autoincrement for this column despite
# the ForeignKey()
Column('id', ForeignKey('other.id'),
            primary_key=True, autoincrement='ignore_fk')
```
  It is typically not desirable to have “autoincrement” enabled on a column that refers to another via foreign key, as such a column is required to refer to a value that originates from elsewhere.
The setting has these two effects on columns that meet the above criteria:
- DDL issued for the column will include database-specific keywords intended to signify this column as an “autoincrement” column, such as AUTO INCREMENT on MySQL, SERIAL on PostgreSQL, and IDENTITY on MS-SQL. It does not issue AUTOINCREMENT for SQLite since this is a special SQLite flag that is not required for autoincrementing behavior.
  
  See also
  
  SQLite Auto Incrementing Behavior
- The column will be considered to be available using an “autoincrement” method specific to the backend database, such as calling upon cursor.lastrowid, using RETURNING in an INSERT statement to get at a sequence-generated value, or using special functions such as “SELECT scope_identity()”. These methods are highly specific to the DBAPIs and databases in use and vary greatly, so care should be taken when associating autoincrement=True with a custom default generation function.
default –
A scalar, Python callable, or ColumnElement expression representing the default value for this column, which will be invoked upon insert if this column is otherwise not specified in the VALUES clause of the insert. This is a shortcut to using ColumnDefault as a positional argument; see that class for full detail on the structure of the argument.

Contrast this argument to Column.server_default which creates a default generator on the database side.

See also

Column Insert/Update Defaults
doc – optional String that can be used by the ORM or similar to document attributes on the Python side. This attribute does not render SQL comments; use the Column.comment parameter for this purpose.
key – An optional string identifier which will identify this Column object on the Table. When a key is provided, this is the only identifier referencing the Column within the application, including ORM attribute mapping; the name field is used only when rendering SQL.
index – When True, indicates that the column is indexed. This is a shortcut for using a Index construct on the table. To specify indexes with explicit names or indexes that contain multiple columns, use the Index construct instead.
info – Optional data dictionary which will be populated into the SchemaItem.info attribute of this object.
nullable – When set to False, will cause the “NOT NULL” phrase to be added when generating DDL for the column. When True, will normally generate nothing (in SQL this defaults to “NULL”), except in some very specific backend-specific edge cases where “NULL” may render explicitly. Defaults to True unless Column.primary_key is also True, in which case it defaults to False. This parameter is only used when issuing CREATE TABLE statements.
onupdate –
A scalar, Python callable, or ClauseElement representing a default value to be applied to the column within UPDATE statements, which will be invoked upon update if this column is not present in the SET clause of the update. This is a shortcut to using ColumnDefault as a positional argument with for_update=True.

See also

Column Insert/Update Defaults - complete discussion of onupdate
primary_key – If True, marks this column as a primary key column. Multiple columns can have this flag set to specify composite primary keys. As an alternative, the primary key of a Table can be specified via an explicit PrimaryKeyConstraint object.
server_default –
A FetchedValue instance, str, Unicode or text() construct representing the DDL DEFAULT value for the column.

String types will be emitted as-is, surrounded by single quotes:
```
Column('x', Text, server_default="val")

x TEXT DEFAULT 'val'
```
A text() expression will be rendered as-is, without quotes:
```
Column('y', DateTime, server_default=text('NOW()'))

y DATETIME DEFAULT NOW()
```
Strings and text() will be converted into a DefaultClause object upon initialization.

Use FetchedValue to indicate that an already-existing column will generate a default value on the database side which will be available to SQLAlchemy for post-fetch after inserts. This construct does not specify any DDL and the implementation is left to the database, such as via a trigger.

See also

Server-invoked DDL-Explicit Default Expressions - complete discussion of server side defaults
server_onupdate –

A FetchedValue instance
representing a database-side default generation function, such as a trigger. This indicates to SQLAlchemy that a newly generated value will be available after updates. This construct does not actually implement any kind of generation function within the database, which instead must be specified separately.

See also

Marking Implicitly Generated Values, timestamps, and Triggered Columns
quote – Force quoting of this column’s name on or off, corresponding to True or False. When left at its default of None, the column identifier will be quoted according to whether the name is case sensitive (identifiers with at least one upper case character are treated as case sensitive), or if it’s a reserved word. This flag is only needed to force quoting of a reserved word which is not known by the SQLAlchemy dialect.
unique – When True, indicates that this column contains a unique constraint, or if index is True as well, indicates that the Index should be created with the unique flag. To specify multiple columns in the constraint/index or to specify an explicit name, use the UniqueConstraint or Index constructs explicitly.
system –
When True, indicates this is a “system” column, that is a column which is automatically made available by the database, and should not be included in the columns list for a CREATE TABLE statement.

For more elaborate scenarios where columns should be conditionally rendered differently on different backends, consider custom compilation rules for CreateColumn.
comment –
Optional string that will render an SQL comment on table creation.

New in version 1.2: Added the Column.comment parameter to Column.

method sqlalchemy.schema.Column.__le__(other)¶

inherited from the sqlalchemy.sql.operators.ColumnOperators.__le__ method of ColumnOperators

Implement the <= operator.

In a column context, produces the clause a <= b.

method sqlalchemy.schema.Column.__lt__(other)¶

inherited from the sqlalchemy.sql.operators.ColumnOperators.__lt__ method of ColumnOperators

Implement the < operator.

In a column context, produces the clause a < b.

method sqlalchemy.schema.Column.__ne__(other)¶

inherited from the sqlalchemy.sql.operators.ColumnOperators.__ne__ method of ColumnOperators

Implement the != operator.

In a column context, produces the clause a != b. If the target is None, produces a IS NOT NULL.

method sqlalchemy.schema.Column.all_()¶

inherited from the ColumnOperators.all_() method of ColumnOperators

Produce a all_() clause against the parent object.

This operator is only appropriate against a scalar subquery object, or for some backends an column expression that is against the ARRAY type, e.g.:

# postgresql '5 = ALL (somearray)'
expr = 5 == mytable.c.somearray.all_()

# mysql '5 = ALL (SELECT value FROM table)'
expr = 5 == select([table.c.value]).as_scalar().all_()

See also

all_() - standalone version

any_() - ANY operator

New in version 1.1.

attribute sqlalchemy.schema.Column.anon_label¶

inherited from the ColumnElement.anon_label attribute of ColumnElement

provides a constant ‘anonymous label’ for this ColumnElement.

This is a label() expression which will be named at compile time. The same label() is returned each time anon_label is called so that expressions can reference anon_label multiple times, producing the same label name at compile time.

the compiler uses this function automatically at compile time for expressions that are known to be ‘unnamed’ like binary expressions and function calls.

method sqlalchemy.schema.Column.any_()¶

inherited from the ColumnOperators.any_() method of ColumnOperators

Produce a any_() clause against the parent object.

This operator is only appropriate against a scalar subquery object, or for some backends an column expression that is against the ARRAY type, e.g.:

# postgresql '5 = ANY (somearray)'
expr = 5 == mytable.c.somearray.any_()

# mysql '5 = ANY (SELECT value FROM table)'
expr = 5 == select([table.c.value]).as_scalar().any_()

See also

any_() - standalone version

all_() - ALL operator

New in version 1.1.

method sqlalchemy.schema.Column.asc()¶: inherited from the ColumnOperators.asc() method of ColumnOperators

Produce a asc() clause against the parent object.

method sqlalchemy.schema.Column.between(cleft, cright, symmetric=False)¶: inherited from the ColumnOperators.between() method of ColumnOperators

Produce a between() clause against the parent object, given the lower and upper range.

method sqlalchemy.schema.Column.bool_op(opstring, precedence=0)¶

inherited from the Operators.bool_op() method of Operators

Return a custom boolean operator.

This method is shorthand for calling Operators.op() and passing the Operators.op.is_comparison flag with True.

New in version 1.2.0b3.

See also

Operators.op()

method sqlalchemy.schema.Column.cast(type_)¶

inherited from the ColumnElement.cast() method of ColumnElement

Produce a type cast, i.e. CAST(<expression> AS <type>).

This is a shortcut to the cast() function.

New in version 1.0.7.

method sqlalchemy.schema.Column.collate(collation)¶: inherited from the ColumnOperators.collate() method of ColumnOperators

Produce a collate() clause against the parent object, given the collation string.

See also

collate()

method sqlalchemy.schema.Column.compare(other, use_proxies=False, equivalents=None, **kw)¶

inherited from the ColumnElement.compare() method of ColumnElement

Compare this ColumnElement to another.

Special arguments understood:

Parameters:

use_proxies – when True, consider two columns that share a common base column as equivalent (i.e. shares_lineage())
equivalents – a dictionary of columns as keys mapped to sets of columns. If the given “other” column is present in this dictionary, if any of the columns in the corresponding set() pass the comparison test, the result is True. This is used to expand the comparison to other columns that may be known to be equivalent to this one via foreign key or other criterion.

method sqlalchemy.schema.Column.compile(default, bind=None, dialect=None, **kw)¶

inherited from the ClauseElement.compile() method of ClauseElement

Compile this SQL expression.

The return value is a Compiled object. Calling str() or unicode() on the returned value will yield a string representation of the result. The Compiled object also can return a dictionary of bind parameter names and values using the params accessor.

Parameters:

bind – An Engine or Connection from which a Compiled will be acquired. This argument takes precedence over this ClauseElement’s bound engine, if any.
column_keys – Used for INSERT and UPDATE statements, a list of column names which should be present in the VALUES clause of the compiled statement. If None, all columns from the target table object are rendered.
dialect – A Dialect instance from which a Compiled will be acquired. This argument takes precedence over the bind argument as well as this ClauseElement’s bound engine, if any.
inline – Used for INSERT statements, for a dialect which does not support inline retrieval of newly generated primary key columns, will force the expression used to create the new primary key value to be rendered inline within the INSERT statement’s VALUES clause. This typically refers to Sequence execution but may also refer to any server-side default generation function associated with a primary key Column.
compile_kwargs –
optional dictionary of additional parameters that will be passed through to the compiler within all “visit” methods. This allows any custom flag to be passed through to a custom compilation construct, for example. It is also used for the case of passing the literal_binds flag through:
```
from sqlalchemy.sql import table, column, select

t = table('t', column('x'))

s = select([t]).where(t.c.x == 5)

print s.compile(compile_kwargs={"literal_binds": True})
```
New in version 0.9.0.

method sqlalchemy.schema.Column.concat(other)¶

inherited from the ColumnOperators.concat() method of ColumnOperators

Implement the ‘concat’ operator.

In a column context, produces the clause a || b, or uses the concat() operator on MySQL.

method sqlalchemy.schema.Column.contains(other, **kwargs)¶

inherited from the ColumnOperators.contains() method of ColumnOperators

Implement the ‘contains’ operator.

Produces a LIKE expression that tests against a match for the middle of a string value:

column LIKE '%' || <other> || '%'

E.g.:

stmt = select([sometable]).\
    where(sometable.c.column.contains("foobar"))

Since the operator uses LIKE, wildcard characters "%" and "_" that are present inside the <other> expression will behave like wildcards as well. For literal string values, the ColumnOperators.contains.autoescape flag may be set to True to apply escaping to occurrences of these characters within the string value so that they match as themselves and not as wildcard characters. Alternatively, the ColumnOperators.contains.escape parameter will establish a given character as an escape character which can be of use when the target expression is not a literal string.

Parameters:

other – expression to be compared. This is usually a plain string value, but can also be an arbitrary SQL expression. LIKE wildcard characters % and _ are not escaped by default unless the ColumnOperators.contains.autoescape flag is set to True.
autoescape –
boolean; when True, establishes an escape character within the LIKE expression, then applies it to all occurrences of "%", "_" and the escape character itself within the comparison value, which is assumed to be a literal string and not a SQL expression.

An expression such as:
```
somecolumn.contains("foo%bar", autoescape=True)
```
Will render as:
```
somecolumn LIKE '%' || :param || '%' ESCAPE '/'
```
With the value of :param as "foo/%bar".

New in version 1.2.

Changed in version 1.2.0: The ColumnOperators.contains.autoescape parameter is now a simple boolean rather than a character; the escape character itself is also escaped, and defaults to a forwards slash, which itself can be customized using the ColumnOperators.contains.escape parameter.
escape –
a character which when given will render with the ESCAPE keyword to establish that character as the escape character. This character can then be placed preceding occurrences of % and _ to allow them to act as themselves and not wildcard characters.

An expression such as:
```
somecolumn.contains("foo/%bar", escape="^")
```
Will render as:
```
somecolumn LIKE '%' || :param || '%' ESCAPE '^'
```
The parameter may also be combined with ColumnOperators.contains.autoescape:
```
somecolumn.contains("foo%bar^bat", escape="^", autoescape=True)
```
Where above, the given literal parameter will be converted to "foo^%bar^^bat" before being passed to the database.

See also

ColumnOperators.startswith()

ColumnOperators.endswith()

ColumnOperators.like()

method sqlalchemy.schema.Column.copy(**kw)¶

Create a copy of this Column, uninitialized.

This is used in Table.tometadata.

method sqlalchemy.schema.Column.desc()¶: inherited from the ColumnOperators.desc() method of ColumnOperators

Produce a desc() clause against the parent object.

method sqlalchemy.schema.Column.distinct()¶: inherited from the ColumnOperators.distinct() method of ColumnOperators

Produce a distinct() clause against the parent object.

method sqlalchemy.schema.Column.endswith(other, **kwargs)¶

inherited from the ColumnOperators.endswith() method of ColumnOperators

Implement the ‘endswith’ operator.

Produces a LIKE expression that tests against a match for the end of a string value:

column LIKE '%' || <other>

E.g.:

stmt = select([sometable]).\
    where(sometable.c.column.endswith("foobar"))

Since the operator uses LIKE, wildcard characters "%" and "_" that are present inside the <other> expression will behave like wildcards as well. For literal string values, the ColumnOperators.endswith.autoescape flag may be set to True to apply escaping to occurrences of these characters within the string value so that they match as themselves and not as wildcard characters. Alternatively, the ColumnOperators.endswith.escape parameter will establish a given character as an escape character which can be of use when the target expression is not a literal string.

Parameters:

other – expression to be compared. This is usually a plain string value, but can also be an arbitrary SQL expression. LIKE wildcard characters % and _ are not escaped by default unless the ColumnOperators.endswith.autoescape flag is set to True.
autoescape –
boolean; when True, establishes an escape character within the LIKE expression, then applies it to all occurrences of "%", "_" and the escape character itself within the comparison value, which is assumed to be a literal string and not a SQL expression.

An expression such as:
```
somecolumn.endswith("foo%bar", autoescape=True)
```
Will render as:
```
somecolumn LIKE '%' || :param ESCAPE '/'
```
With the value of :param as "foo/%bar".

New in version 1.2.

Changed in version 1.2.0: The ColumnOperators.endswith.autoescape parameter is now a simple boolean rather than a character; the escape character itself is also escaped, and defaults to a forwards slash, which itself can be customized using the ColumnOperators.endswith.escape parameter.
escape –
a character which when given will render with the ESCAPE keyword to establish that character as the escape character. This character can then be placed preceding occurrences of % and _ to allow them to act as themselves and not wildcard characters.

An expression such as:
```
somecolumn.endswith("foo/%bar", escape="^")
```
Will render as:
```
somecolumn LIKE '%' || :param ESCAPE '^'
```
The parameter may also be combined with ColumnOperators.endswith.autoescape:
```
somecolumn.endswith("foo%bar^bat", escape="^", autoescape=True)
```
Where above, the given literal parameter will be converted to "foo^%bar^^bat" before being passed to the database.

See also

ColumnOperators.startswith()

ColumnOperators.contains()

ColumnOperators.like()

attribute sqlalchemy.schema.Column.expression¶

inherited from the ColumnElement.expression attribute of ColumnElement

Return a column expression.

Part of the inspection interface; returns self.

method sqlalchemy.schema.Column.get_children(schema_visitor=False, **kwargs)¶: used to allow SchemaVisitor access

method sqlalchemy.schema.Column.ilike(other, escape=None)¶

inherited from the ColumnOperators.ilike() method of ColumnOperators

Implement the ilike operator, e.g. case insensitive LIKE.

In a column context, produces an expression either of the form:

lower(a) LIKE lower(other)

Or on backends that support the ILIKE operator:

a ILIKE other

E.g.:

stmt = select([sometable]).\
    where(sometable.c.column.ilike("%foobar%"))

Parameters:

other – expression to be compared
escape –
optional escape character, renders the ESCAPE keyword, e.g.:
```
somecolumn.ilike("foo/%bar", escape="/")
```

See also

ColumnOperators.like()

method sqlalchemy.schema.Column.in_(other)¶

inherited from the ColumnOperators.in_() method of ColumnOperators

Implement the in operator.

In a column context, produces the clause column IN <other>.

The given parameter other may be:

A list of literal values, e.g.:
```
stmt.where(column.in_([1, 2, 3]))
```
In this calling form, the list of items is converted to a set of bound parameters the same length as the list given:
```
WHERE COL IN (?, ?, ?)
```
An empty list, e.g.:
```
stmt.where(column.in_([]))
```
In this calling form, the expression renders a “false” expression, e.g.:
```
WHERE 1 != 1
```
This “false” expression has historically had different behaviors in older SQLAlchemy versions, see create_engine.empty_in_strategy for behavioral options.

Changed in version 1.2: simplified the behavior of “empty in” expressions
A bound parameter, e.g. bindparam(), may be used if it includes the bindparam.expanding flag:
```
stmt.where(column.in_(bindparam('value', expanding=True)))
```
In this calling form, the expression renders a special non-SQL placeholder expression that looks like:
```
WHERE COL IN ([EXPANDING_value])
```
This placeholder expression is intercepted at statement execution time to be converted into the variable number of bound parameter form illustrated earlier. If the statement were executed as:
```
connection.execute(stmt, {"value": [1, 2, 3]})
```
The database would be passed a bound parameter for each value:
```
WHERE COL IN (?, ?, ?)
```
New in version 1.2: added “expanding” bound parameters

The “expanding” feature in version 1.2 of SQLAlchemy does not support passing an empty list as a parameter value; however, version 1.3 does support this.

a select() construct, which is usually a correlated scalar select:

stmt.where(
    column.in_(
        select([othertable.c.y]).
        where(table.c.x == othertable.c.x)
    )
)

In this calling form, ColumnOperators.in_() renders as given:

WHERE COL IN (SELECT othertable.y
FROM othertable WHERE othertable.x = table.x)

Parameters:: other – a list of literals, a select() construct, or a bindparam() construct that includes the bindparam.expanding flag set to True.

attribute sqlalchemy.schema.Column.info¶

inherited from the SchemaItem.info attribute of SchemaItem

Info dictionary associated with the object, allowing user-defined data to be associated with this SchemaItem.

The dictionary is automatically generated when first accessed. It can also be specified in the constructor of some objects, such as Table and Column.

method sqlalchemy.schema.Column.is_(other)¶

inherited from the ColumnOperators.is_() method of ColumnOperators

Implement the IS operator.

Normally, IS is generated automatically when comparing to a value of None, which resolves to NULL. However, explicit usage of IS may be desirable if comparing to boolean values on certain platforms.

See also

ColumnOperators.isnot()

method sqlalchemy.schema.Column.is_distinct_from(other)¶

inherited from the ColumnOperators.is_distinct_from() method of ColumnOperators

Implement the IS DISTINCT FROM operator.

Renders “a IS DISTINCT FROM b” on most platforms; on some such as SQLite may render “a IS NOT b”.

New in version 1.1.

method sqlalchemy.schema.Column.isnot(other)¶

inherited from the ColumnOperators.isnot() method of ColumnOperators

Implement the IS NOT operator.

Normally, IS NOT is generated automatically when comparing to a value of None, which resolves to NULL. However, explicit usage of IS NOT may be desirable if comparing to boolean values on certain platforms.

See also

ColumnOperators.is_()

method sqlalchemy.schema.Column.isnot_distinct_from(other)¶

inherited from the ColumnOperators.isnot_distinct_from() method of ColumnOperators

Implement the IS NOT DISTINCT FROM operator.

Renders “a IS NOT DISTINCT FROM b” on most platforms; on some such as SQLite may render “a IS b”.

New in version 1.1.

attribute sqlalchemy.schema.Column.key = None¶

inherited from the ColumnElement.key attribute of ColumnElement

the ‘key’ that in some circumstances refers to this object in a Python namespace.

This typically refers to the “key” of the column as present in the .c collection of a selectable, e.g. sometable.c[“somekey”] would return a Column with a .key of “somekey”.

method sqlalchemy.schema.Column.label(name)¶

inherited from the ColumnElement.label() method of ColumnElement

Produce a column label, i.e. <columnname> AS <name>.

This is a shortcut to the label() function.

if ‘name’ is None, an anonymous label name will be generated.

method sqlalchemy.schema.Column.like(other, escape=None)¶

inherited from the ColumnOperators.like() method of ColumnOperators

Implement the like operator.

In a column context, produces the expression:

a LIKE other

E.g.:

stmt = select([sometable]).\
    where(sometable.c.column.like("%foobar%"))

Parameters:

other – expression to be compared
escape –
optional escape character, renders the ESCAPE keyword, e.g.:
```
somecolumn.like("foo/%bar", escape="/")
```

See also

ColumnOperators.ilike()

method sqlalchemy.schema.Column.match(other, **kwargs)¶

inherited from the ColumnOperators.match() method of ColumnOperators

Implements a database-specific ‘match’ operator.

ColumnOperators.match() attempts to resolve to a MATCH-like function or operator provided by the backend. Examples include:

PostgreSQL - renders x @@ to_tsquery(y)
MySQL - renders MATCH (x) AGAINST (y IN BOOLEAN MODE)
Oracle - renders CONTAINS(x, y)
other backends may provide special implementations.
Backends without any special implementation will emit the operator as “MATCH”. This is compatible with SQLite, for example.

method sqlalchemy.schema.Column.notilike(other, escape=None)¶

inherited from the ColumnOperators.notilike() method of ColumnOperators

implement the NOT ILIKE operator.

This is equivalent to using negation with ColumnOperators.ilike(), i.e. ~x.ilike(y).

See also

ColumnOperators.ilike()

method sqlalchemy.schema.Column.notin_(other)¶

inherited from the ColumnOperators.notin_() method of ColumnOperators

implement the NOT IN operator.

This is equivalent to using negation with ColumnOperators.in_(), i.e. ~x.in_(y).

In the case that other is an empty sequence, the compiler produces an “empty not in” expression. This defaults to the expression “1 = 1” to produce true in all cases. The create_engine.empty_in_strategy may be used to alter this behavior.

Changed in version 1.2: The ColumnOperators.in_() and ColumnOperators.notin_() operators now produce a “static” expression for an empty IN sequence by default.

See also

ColumnOperators.in_()

method sqlalchemy.schema.Column.notlike(other, escape=None)¶

inherited from the ColumnOperators.notlike() method of ColumnOperators

implement the NOT LIKE operator.

This is equivalent to using negation with ColumnOperators.like(), i.e. ~x.like(y).

See also

ColumnOperators.like()

method sqlalchemy.schema.Column.nullsfirst()¶: inherited from the ColumnOperators.nullsfirst() method of ColumnOperators

Produce a nullsfirst() clause against the parent object.

method sqlalchemy.schema.Column.nullslast()¶: inherited from the ColumnOperators.nullslast() method of ColumnOperators

Produce a nullslast() clause against the parent object.

method sqlalchemy.schema.Column.op(opstring, precedence=0, is_comparison=False, return_type=None)¶

inherited from the Operators.op() method of Operators

produce a generic operator function.

e.g.:

somecolumn.op("*")(5)

produces:

somecolumn * 5

This function can also be used to make bitwise operators explicit. For example:

somecolumn.op('&')(0xff)

is a bitwise AND of the value in somecolumn.

Parameters:

operator – a string which will be output as the infix operator between this element and the expression passed to the generated function.
precedence – precedence to apply to the operator, when parenthesizing expressions. A lower number will cause the expression to be parenthesized when applied against another operator with higher precedence. The default value of 0 is lower than all operators except for the comma (,) and AS operators. A value of 100 will be higher or equal to all operators, and -100 will be lower than or equal to all operators.
is_comparison –
if True, the operator will be considered as a “comparison” operator, that is which evaluates to a boolean true/false value, like ==, >, etc. This flag should be set so that ORM relationships can establish that the operator is a comparison operator when used in a custom join condition.

New in version 0.9.2: - added the Operators.op.is_comparison flag.
return_type –
a TypeEngine class or object that will force the return type of an expression produced by this operator to be of that type. By default, operators that specify Operators.op.is_comparison will resolve to Boolean, and those that do not will be of the same type as the left-hand operand.

New in version 1.2.0b3: - added the Operators.op.return_type argument.

See also

Redefining and Creating New Operators

Using custom operators in join conditions

method sqlalchemy.schema.Column.operate(op, *other, **kwargs)¶

inherited from the ColumnElement.operate() method of ColumnElement

Operate on an argument.

This is the lowest level of operation, raises NotImplementedError by default.

Overriding this on a subclass can allow common behavior to be applied to all operations. For example, overriding ColumnOperators to apply func.lower() to the left and right side:

class MyComparator(ColumnOperators):
    def operate(self, op, other):
        return op(func.lower(self), func.lower(other))

Parameters:

op – Operator callable.
*other – the ‘other’ side of the operation. Will be a single scalar for most operations.
**kwargs – modifiers. These may be passed by special operators such as ColumnOperators.contains().

method sqlalchemy.schema.Column.params(*optionaldict, **kwargs)¶

inherited from the Immutable.params() method of Immutable

Return a copy with bindparam() elements replaced.

Returns a copy of this ClauseElement with bindparam() elements replaced with values taken from the given dictionary:

>>> clause = column('x') + bindparam('foo')
>>> print clause.compile().params
{'foo':None}
>>> print clause.params({'foo':7}).compile().params
{'foo':7}

attribute sqlalchemy.schema.Column.quote¶: inherited from the SchemaItem.quote attribute of SchemaItem

Return the value of the quote flag passed to this schema object, for those schema items which have a name field.

Deprecated since version 0.9: The SchemaItem.quote attribute is deprecated and will be removed in a future release. Use the quoted_name.quote attribute on the name field of the target schema item to retrievequoted status.

method sqlalchemy.schema.Column.references(column)¶: Return True if this Column references the given column via foreign key.

method sqlalchemy.schema.Column.reverse_operate(op, other, **kwargs)¶

inherited from the ColumnElement.reverse_operate() method of ColumnElement

Reverse operate on an argument.

Usage is the same as operate().

method sqlalchemy.schema.Column.self_group(against=None)¶

inherited from the ColumnElement.self_group() method of ColumnElement

Apply a ‘grouping’ to this ClauseElement.

This method is overridden by subclasses to return a “grouping” construct, i.e. parenthesis. In particular it’s used by “binary” expressions to provide a grouping around themselves when placed into a larger expression, as well as by select() constructs when placed into the FROM clause of another select(). (Note that subqueries should be normally created using the Select.alias() method, as many platforms require nested SELECT statements to be named).

As expressions are composed together, the application of self_group() is automatic - end-user code should never need to use this method directly. Note that SQLAlchemy’s clause constructs take operator precedence into account - so parenthesis might not be needed, for example, in an expression like x OR (y AND z) - AND takes precedence over OR.

The base self_group() method of ClauseElement just returns self.

method sqlalchemy.schema.Column.shares_lineage(othercolumn)¶: inherited from the ColumnElement.shares_lineage() method of ColumnElement

Return True if the given ColumnElement has a common ancestor to this ColumnElement.

method sqlalchemy.schema.Column.startswith(other, **kwargs)¶

inherited from the ColumnOperators.startswith() method of ColumnOperators

Implement the startswith operator.

Produces a LIKE expression that tests against a match for the start of a string value:

column LIKE <other> || '%'

E.g.:

stmt = select([sometable]).\
    where(sometable.c.column.startswith("foobar"))

Since the operator uses LIKE, wildcard characters "%" and "_" that are present inside the <other> expression will behave like wildcards as well. For literal string values, the ColumnOperators.startswith.autoescape flag may be set to True to apply escaping to occurrences of these characters within the string value so that they match as themselves and not as wildcard characters. Alternatively, the ColumnOperators.startswith.escape parameter will establish a given character as an escape character which can be of use when the target expression is not a literal string.

Parameters:

other – expression to be compared. This is usually a plain string value, but can also be an arbitrary SQL expression. LIKE wildcard characters % and _ are not escaped by default unless the ColumnOperators.startswith.autoescape flag is set to True.
autoescape –
boolean; when True, establishes an escape character within the LIKE expression, then applies it to all occurrences of "%", "_" and the escape character itself within the comparison value, which is assumed to be a literal string and not a SQL expression.

An expression such as:
```
somecolumn.startswith("foo%bar", autoescape=True)
```
Will render as:
```
somecolumn LIKE :param || '%' ESCAPE '/'
```
With the value of :param as "foo/%bar".

New in version 1.2.

Changed in version 1.2.0: The ColumnOperators.startswith.autoescape parameter is now a simple boolean rather than a character; the escape character itself is also escaped, and defaults to a forwards slash, which itself can be customized using the ColumnOperators.startswith.escape parameter.
escape –
a character which when given will render with the ESCAPE keyword to establish that character as the escape character. This character can then be placed preceding occurrences of % and _ to allow them to act as themselves and not wildcard characters.

An expression such as:
```
somecolumn.startswith("foo/%bar", escape="^")
```
Will render as:
```
somecolumn LIKE :param || '%' ESCAPE '^'
```
The parameter may also be combined with ColumnOperators.startswith.autoescape:
```
somecolumn.startswith("foo%bar^bat", escape="^", autoescape=True)
```
Where above, the given literal parameter will be converted to "foo^%bar^^bat" before being passed to the database.

See also

ColumnOperators.endswith()

ColumnOperators.contains()

ColumnOperators.like()

attribute sqlalchemy.schema.Column.timetuple = None¶: inherited from the ColumnOperators.timetuple attribute of ColumnOperators

Hack, allows datetime objects to be compared on the LHS.

method sqlalchemy.schema.Column.unique_params(*optionaldict, **kwargs)¶

inherited from the Immutable.unique_params() method of Immutable

Return a copy with bindparam() elements replaced.

Same functionality as params(), except adds unique=True to affected bind parameters so that multiple statements can be used.

class sqlalchemy.schema.MetaData(bind=None, reflect=False, schema=None, quote_schema=None, naming_convention={'ix': 'ix_%(column_0_label)s'}, info=None)¶

A collection of Table objects and their associated schema constructs.

Holds a collection of Table objects as well as an optional binding to an Engine or Connection. If bound, the Table objects in the collection and their columns may participate in implicit SQL execution.

The Table objects themselves are stored in the MetaData.tables dictionary.

MetaData is a thread-safe object for read operations. Construction of new tables within a single MetaData object, either explicitly or via reflection, may not be completely thread-safe.

See also

Describing Databases with MetaData - Introduction to database metadata

Members

__init__(), append_ddl_listener(), bind, clear(), create_all(), drop_all(), is_bound(), reflect(), remove(), sorted_tables, tables

Class signature

class sqlalchemy.schema.MetaData (sqlalchemy.schema.SchemaItem)

method sqlalchemy.schema.MetaData.__init__(bind=None, reflect=False, schema=None, quote_schema=None, naming_convention={'ix': 'ix_%(column_0_label)s'}, info=None)¶

Create a new MetaData object.

Parameters:

bind – An Engine or Connection to bind to. May also be a string or URL instance, these are passed to create_engine() and this MetaData will be bound to the resulting engine.
reflect –
Optional, automatically load all tables from the bound database. Defaults to False. bind is required when this option is set.

Deprecated since version 0.8: The MetaData.reflect flag is deprecated and will be removed in a future release. Please use the MetaData.reflect() method.
schema –
The default schema to use for the Table, Sequence, and potentially other objects associated with this MetaData. Defaults to None.

When this value is set, any Table or Sequence which specifies None for the schema parameter will instead have this schema name defined. To build a Table or Sequence that still has None for the schema even when this parameter is present, use the BLANK_SCHEMA symbol.

Note

As refered above, the MetaData.schema parameter only refers to the default value that will be applied to the Table.schema parameter of an incoming Table object. It does not refer to how the Table is catalogued within the MetaData, which remains consistent vs. a MetaData collection that does not define this parameter. The Table within the MetaData will still be keyed based on its schema-qualified name, e.g. my_metadata.tables["some_schema.my_table"].

The current behavior of the ForeignKey object is to circumvent this restriction, where it can locate a table given the table name alone, where the schema will be assumed to be present from this value as specified on the owning MetaData collection. However, this implies that a table qualified with BLANK_SCHEMA cannot currently be referred to by string name from ForeignKey. Other parts of SQLAlchemy such as Declarative may not have similar behaviors built in, however may do so in a future release, along with a consistent method of referring to a table in BLANK_SCHEMA.

See also

Table.schema

Sequence.schema
quote_schema – Sets the quote_schema flag for those Table, Sequence, and other objects which make usage of the local schema name.
info –
Optional data dictionary which will be populated into the SchemaItem.info attribute of this object.

New in version 1.0.0.
naming_convention –
a dictionary referring to values which will establish default naming conventions for Constraint and Index objects, for those objects which are not given a name explicitly.

The keys of this dictionary may be:
- a constraint or Index class, e.g. the UniqueConstraint, ForeignKeyConstraint class, the Index class
- a string mnemonic for one of the known constraint classes; "fk", "pk", "ix", "ck", "uq" for foreign key, primary key, index, check, and unique constraint, respectively.
- the string name of a user-defined “token” that can be used to define new naming tokens.
The values associated with each “constraint class” or “constraint mnemonic” key are string naming templates, such as "uq_%(table_name)s_%(column_0_name)s", which describe how the name should be composed. The values associated with user-defined “token” keys should be callables of the form fn(constraint, table), which accepts the constraint/index object and Table as arguments, returning a string result.

The built-in names are as follows, some of which may only be available for certain types of constraint:
- %(table_name)s - the name of the Table object associated with the constraint.
- %(referred_table_name)s - the name of the Table object associated with the referencing target of a ForeignKeyConstraint.
- %(column_0_name)s - the name of the Column at index position “0” within the constraint.
- %(column_0_label)s - the label of the Column at index position “0”, e.g. Column.label
- %(column_0_key)s - the key of the Column at index position “0”, e.g. Column.key
- %(referred_column_0_name)s - the name of a Column at index position “0” referenced by a ForeignKeyConstraint.
- %(constraint_name)s - a special key that refers to the existing name given to the constraint. When this key is present, the Constraint object’s existing name will be replaced with one that is composed from template string that uses this token. When this token is present, it is required that the Constraint is given an explicit name ahead of time.
- user-defined: any additional token may be implemented by passing it along with a fn(constraint, table) callable to the naming_convention dictionary.
New in version 0.9.2.

See also

Configuring Constraint Naming Conventions - for detailed usage examples.

method sqlalchemy.schema.MetaData.append_ddl_listener(event_name, listener)¶: Append a DDL event listener to this MetaData.

Deprecated since version 0.7: See DDLEvents.

attribute sqlalchemy.schema.MetaData.bind¶

An Engine or Connection to which this MetaData is bound.

Typically, a Engine is assigned to this attribute so that “implicit execution” may be used, or alternatively as a means of providing engine binding information to an ORM Session object:

engine = create_engine("someurl://")
metadata.bind = engine

See also

Connectionless Execution, Implicit Execution - background on “bound metadata”

method sqlalchemy.schema.MetaData.clear()¶: Clear all Table objects from this MetaData.

method sqlalchemy.schema.MetaData.create_all(bind=None, tables=None, checkfirst=True)¶

Create all tables stored in this metadata.

Conditional by default, will not attempt to recreate tables already present in the target database.

Parameters:

bind – A Connectable used to access the database; if None, uses the existing bind on this MetaData, if any.
tables – Optional list of Table objects, which is a subset of the total tables in the MetaData (others are ignored).
checkfirst – Defaults to True, don’t issue CREATEs for tables already present in the target database.

method sqlalchemy.schema.MetaData.drop_all(bind=None, tables=None, checkfirst=True)¶

Drop all tables stored in this metadata.

Conditional by default, will not attempt to drop tables not present in the target database.

Parameters:

bind – A Connectable used to access the database; if None, uses the existing bind on this MetaData, if any.
tables – Optional list of Table objects, which is a subset of the total tables in the MetaData (others are ignored).
checkfirst – Defaults to True, only issue DROPs for tables confirmed to be present in the target database.

method sqlalchemy.schema.MetaData.is_bound()¶: True if this MetaData is bound to an Engine or Connection.

method sqlalchemy.schema.MetaData.reflect(bind=None, schema=None, views=False, only=None, extend_existing=False, autoload_replace=True, **dialect_kwargs)¶

Load all available table definitions from the database.

Automatically creates Table entries in this MetaData for any table available in the database but not yet present in the MetaData. May be called multiple times to pick up tables recently added to the database, however no special action is taken if a table in this MetaData no longer exists in the database.

Parameters:

bind – A Connectable used to access the database; if None, uses the existing bind on this MetaData, if any.
schema – Optional, query and reflect tables from an alternate schema. If None, the schema associated with this MetaData is used, if any.
views – If True, also reflect views.
only –
Optional. Load only a sub-set of available named tables. May be specified as a sequence of names or a callable.

If a sequence of names is provided, only those tables will be reflected. An error is raised if a table is requested but not available. Named tables already present in this MetaData are ignored.

If a callable is provided, it will be used as a boolean predicate to filter the list of potential table names. The callable is called with a table name and this MetaData instance as positional arguments and should return a true value for any table to reflect.
extend_existing –
Passed along to each Table as Table.extend_existing.

New in version 0.9.1.
autoload_replace –
Passed along to each Table as Table.autoload_replace.

New in version 0.9.1.
**dialect_kwargs –
Additional keyword arguments not mentioned above are dialect specific, and passed in the form <dialectname>_<argname>. See the documentation regarding an individual dialect at Dialects for detail on documented arguments.

New in version 0.9.2: - Added MetaData.reflect.**dialect_kwargs to support dialect-level reflection options for all Table objects reflected.

method sqlalchemy.schema.MetaData.remove(table)¶: Remove the given Table object from this MetaData.

attribute sqlalchemy.schema.MetaData.sorted_tables¶

Returns a list of Table objects sorted in order of foreign key dependency.

The sorting will place Table objects that have dependencies first, before the dependencies themselves, representing the order in which they can be created. To get the order in which the tables would be dropped, use the reversed() Python built-in.

Warning

The sorted_tables accessor cannot by itself accommodate automatic resolution of dependency cycles between tables, which are usually caused by mutually dependent foreign key constraints. To resolve these cycles, either the ForeignKeyConstraint.use_alter parameter may be applied to those constraints, or use the sort_tables_and_constraints() function which will break out foreign key constraints involved in cycles separately.

See also

sort_tables()

sort_tables_and_constraints()

MetaData.tables

Inspector.get_table_names()

Inspector.get_sorted_table_and_fkc_names()

attribute sqlalchemy.schema.MetaData.tables = None¶

A dictionary of Table objects keyed to their name or “table key”.

The exact key is that determined by the Table.key attribute; for a table with no Table.schema attribute, this is the same as Table.name. For a table with a schema, it is typically of the form schemaname.tablename.

See also

MetaData.sorted_tables

class sqlalchemy.schema.SchemaItem¶

Base class for items that define a database schema.

Members

get_children(), info, quote

Class signature

class sqlalchemy.schema.SchemaItem (sqlalchemy.sql.expression.SchemaEventTarget, sqlalchemy.sql.visitors.Visitable)

method sqlalchemy.schema.SchemaItem.get_children(**kwargs)¶: used to allow SchemaVisitor access

attribute sqlalchemy.schema.SchemaItem.info¶

Info dictionary associated with the object, allowing user-defined data to be associated with this SchemaItem.

The dictionary is automatically generated when first accessed. It can also be specified in the constructor of some objects, such as Table and Column.

attribute sqlalchemy.schema.SchemaItem.quote¶: Return the value of the quote flag passed to this schema object, for those schema items which have a name field.

Deprecated since version 0.9: The SchemaItem.quote attribute is deprecated and will be removed in a future release. Use the quoted_name.quote attribute on the name field of the target schema item to retrievequoted status.

class sqlalchemy.schema.Table(*args, **kw)¶

Represent a table in a database.

e.g.:

mytable = Table("mytable", metadata,
                Column('mytable_id', Integer, primary_key=True),
                Column('value', String(50))
           )

The Table object constructs a unique instance of itself based on its name and optional schema name within the given MetaData object. Calling the Table constructor with the same name and same MetaData argument a second time will return the same Table object - in this way the Table constructor acts as a registry function.

See also

Describing Databases with MetaData - Introduction to database metadata

Constructor arguments are as follows:

Parameters:

name –
The name of this table as represented in the database.

The table name, along with the value of the schema parameter, forms a key which uniquely identifies this Table within the owning MetaData collection. Additional calls to Table with the same name, metadata, and schema name will return the same Table object.

Names which contain no upper case characters will be treated as case insensitive names, and will not be quoted unless they are a reserved word or contain special characters. A name with any number of upper case characters is considered to be case sensitive, and will be sent as quoted.

To enable unconditional quoting for the table name, specify the flag quote=True to the constructor, or use the quoted_name construct to specify the name.
metadata – a MetaData object which will contain this table. The metadata is used as a point of association of this table with other tables which are referenced via foreign key. It also may be used to associate this table with a particular Connectable.
*args – Additional positional arguments are used primarily to add the list of Column objects contained within this table. Similar to the style of a CREATE TABLE statement, other SchemaItem constructs may be added here, including PrimaryKeyConstraint, and ForeignKeyConstraint.
autoload –
Defaults to False, unless Table.autoload_with is set in which case it defaults to True; Column objects for this table should be reflected from the database, possibly augmenting or replacing existing Column objects that were explicitly specified.

Changed in version 1.0.0: setting the Table.autoload_with parameter implies that Table.autoload will default to True.

See also

Reflecting Database Objects
autoload_replace –
Defaults to True; when using Table.autoload in conjunction with Table.extend_existing, indicates that Column objects present in the already-existing Table object should be replaced with columns of the same name retrieved from the autoload process. When False, columns already present under existing names will be omitted from the reflection process.

Note that this setting does not impact Column objects specified programmatically within the call to Table that also is autoloading; those Column objects will always replace existing columns of the same name when Table.extend_existing is True.

See also

Table.autoload

Table.extend_existing
autoload_with –
An Engine or Connection object with which this Table object will be reflected; when set to a non-None value, it implies that Table.autoload is True. If left unset, but Table.autoload is explicitly set to True, an autoload operation will attempt to proceed by locating an Engine or Connection bound to the underlying MetaData object.

See also

Table.autoload
extend_existing –
When True, indicates that if this Table is already present in the given MetaData, apply further arguments within the constructor to the existing Table.

If Table.extend_existing or Table.keep_existing are not set, and the given name of the new Table refers to a Table that is already present in the target MetaData collection, and this Table specifies additional columns or other constructs or flags that modify the table’s state, an error is raised. The purpose of these two mutually-exclusive flags is to specify what action should be taken when a Table is specified that matches an existing Table, yet specifies additional constructs.

Table.extend_existing will also work in conjunction with Table.autoload to run a new reflection operation against the database, even if a Table of the same name is already present in the target MetaData; newly reflected Column objects and other options will be added into the state of the Table, potentially overwriting existing columns and options of the same name.

As is always the case with Table.autoload, Column objects can be specified in the same Table constructor, which will take precedence. Below, the existing table mytable will be augmented with Column objects both reflected from the database, as well as the given Column named “y”:
```
Table("mytable", metadata,
            Column('y', Integer),
            extend_existing=True,
            autoload=True,
            autoload_with=engine
        )
```
See also

Table.autoload

Table.autoload_replace

Table.keep_existing
implicit_returning – True by default - indicates that RETURNING can be used by default to fetch newly inserted primary key values, for backends which support this. Note that create_engine() also provides an implicit_returning flag.
include_columns – A list of strings indicating a subset of columns to be loaded via the autoload operation; table columns who aren’t present in this list will not be represented on the resulting Table object. Defaults to None which indicates all columns should be reflected.
info – Optional data dictionary which will be populated into the SchemaItem.info attribute of this object.
keep_existing –
When True, indicates that if this Table is already present in the given MetaData, ignore further arguments within the constructor to the existing Table, and return the Table object as originally created. This is to allow a function that wishes to define a new Table on first call, but on subsequent calls will return the same Table, without any of the declarations (particularly constraints) being applied a second time.

If Table.extend_existing or Table.keep_existing are not set, and the given name of the new Table refers to a Table that is already present in the target MetaData collection, and this Table specifies additional columns or other constructs or flags that modify the table’s state, an error is raised. The purpose of these two mutually-exclusive flags is to specify what action should be taken when a Table is specified that matches an existing Table, yet specifies additional constructs.

See also

Table.extend_existing
listeners –
A list of tuples of the form (<eventname>, <fn>) which will be passed to listen() upon construction. This alternate hook to listen() allows the establishment of a listener function specific to this Table before the “autoload” process begins. Particularly useful for the DDLEvents.column_reflect() event:
```
def listen_for_reflect(table, column_info):
    "handle the column reflection event"
    # ...

t = Table(
    'sometable',
    autoload=True,
    listeners=[
        ('column_reflect', listen_for_reflect)
    ])
```
mustexist – When True, indicates that this Table must already be present in the given MetaData collection, else an exception is raised.
prefixes – A list of strings to insert after CREATE in the CREATE TABLE statement. They will be separated by spaces.
quote – Force quoting of this table’s name on or off, corresponding to True or False. When left at its default of None, the column identifier will be quoted according to whether the name is case sensitive (identifiers with at least one upper case character are treated as case sensitive), or if it’s a reserved word. This flag is only needed to force quoting of a reserved word which is not known by the SQLAlchemy dialect.
quote_schema – same as ‘quote’ but applies to the schema identifier.
schema –
The schema name for this table, which is required if the table resides in a schema other than the default selected schema for the engine’s database connection. Defaults to None.

If the owning MetaData of this Table specifies its own MetaData.schema parameter, then that schema name will be applied to this Table if the schema parameter here is set to None. To set a blank schema name on a Table that would otherwise use the schema set on the owning MetaData, specify the special symbol BLANK_SCHEMA.

New in version 1.0.14: Added the BLANK_SCHEMA symbol to allow a Table to have a blank schema name even when the parent MetaData specifies MetaData.schema.

The quoting rules for the schema name are the same as those for the name parameter, in that quoting is applied for reserved words or case-sensitive names; to enable unconditional quoting for the schema name, specify the flag quote_schema=True to the constructor, or use the quoted_name construct to specify the name.
useexisting – Deprecated. Use Table.extend_existing.
comment –
Optional string that will render an SQL comment on table creation.

New in version 1.2: Added the Table.comment parameter to Table.
**kw – Additional keyword arguments not mentioned above are dialect specific, and passed in the form <dialectname>_<argname>. See the documentation regarding an individual dialect at Dialects for detail on documented arguments.

Class signature

class sqlalchemy.schema.Table (sqlalchemy.sql.base.DialectKWArgs, sqlalchemy.schema.SchemaItem, sqlalchemy.sql.expression.TableClause)

method sqlalchemy.schema.Table.__init__(*args, **kw)¶

Constructor for Table.

This method is a no-op. See the top-level documentation for Table for constructor arguments.

method sqlalchemy.schema.Table.add_is_dependent_on(table)¶

Add a ‘dependency’ for this Table.

This is another Table object which must be created first before this one can, or dropped after this one.

Usually, dependencies between tables are determined via ForeignKey objects. However, for other situations that create dependencies outside of foreign keys (rules, inheriting), this method can manually establish such a link.

method sqlalchemy.schema.Table.alias(name=None, flat=False)¶

inherited from the FromClause.alias() method of FromClause

return an alias of this FromClause.

This is shorthand for calling:

from sqlalchemy import alias
a = alias(self, name=name)

See alias() for details.

method sqlalchemy.schema.Table.append_column(column)¶

Append a Column to this Table.

The “key” of the newly added Column, i.e. the value of its .key attribute, will then be available in the .c collection of this Table, and the column definition will be included in any CREATE TABLE, SELECT, UPDATE, etc. statements generated from this Table construct.

Note that this does not change the definition of the table as it exists within any underlying database, assuming that table has already been created in the database. Relational databases support the addition of columns to existing tables using the SQL ALTER command, which would need to be emitted for an already-existing table that doesn’t contain the newly added column.

method sqlalchemy.schema.Table.append_constraint(constraint)¶

Append a Constraint to this Table.

This has the effect of the constraint being included in any future CREATE TABLE statement, assuming specific DDL creation events have not been associated with the given Constraint object.

Note that this does not produce the constraint within the relational database automatically, for a table that already exists in the database. To add a constraint to an existing relational database table, the SQL ALTER command must be used. SQLAlchemy also provides the AddConstraint construct which can produce this SQL when invoked as an executable clause.

method sqlalchemy.schema.Table.append_ddl_listener(event_name, listener)¶: Append a DDL event listener to this Table.

Deprecated since version 0.7: See DDLEvents.

classmethod sqlalchemy.schema.Table.argument_for(dialect_name, argument_name, default)¶

inherited from the DialectKWArgs.argument_for() method of DialectKWArgs

Add a new kind of dialect-specific keyword argument for this class.

E.g.:

Index.argument_for("mydialect", "length", None)

some_index = Index('a', 'b', mydialect_length=5)

The DialectKWArgs.argument_for() method is a per-argument way adding extra arguments to the DefaultDialect.construct_arguments dictionary. This dictionary provides a list of argument names accepted by various schema-level constructs on behalf of a dialect.

New dialects should typically specify this dictionary all at once as a data member of the dialect class. The use case for ad-hoc addition of argument names is typically for end-user code that is also using a custom compilation scheme which consumes the additional arguments.

Parameters:

dialect_name – name of a dialect. The dialect must be locatable, else a NoSuchModuleError is raised. The dialect must also include an existing DefaultDialect.construct_arguments collection, indicating that it participates in the keyword-argument validation and default system, else ArgumentError is raised. If the dialect does not include this collection, then any keyword argument can be specified on behalf of this dialect already. All dialects packaged within SQLAlchemy include this collection, however for third party dialects, support may vary.
argument_name – name of the parameter.
default – default value of the parameter.

New in version 0.9.4.

attribute sqlalchemy.schema.Table.bind¶: Return the connectable associated with this Table.

attribute sqlalchemy.schema.Table.c¶: inherited from the FromClause.c attribute of FromClause

An alias for the columns attribute.

attribute sqlalchemy.schema.Table.columns¶

inherited from the FromClause.columns attribute of FromClause

A named-based collection of ColumnElement objects maintained by this FromClause.

The columns, or c collection, is the gateway to the construction of SQL expressions using table-bound or other selectable-bound columns:

select([mytable]).where(mytable.c.somecolumn == 5)

method sqlalchemy.schema.Table.compare(other, **kw)¶

inherited from the ClauseElement.compare() method of ClauseElement

Compare this ClauseElement to the given ClauseElement.

Subclasses should override the default behavior, which is a straight identity comparison.

**kw are arguments consumed by subclass compare() methods and may be used to modify the criteria for comparison. (see ColumnElement)

method sqlalchemy.schema.Table.compile(default, bind=None, dialect=None, **kw)¶

inherited from the ClauseElement.compile() method of ClauseElement

Compile this SQL expression.

The return value is a Compiled object. Calling str() or unicode() on the returned value will yield a string representation of the result. The Compiled object also can return a dictionary of bind parameter names and values using the params accessor.

Parameters:

bind – An Engine or Connection from which a Compiled will be acquired. This argument takes precedence over this ClauseElement’s bound engine, if any.
column_keys – Used for INSERT and UPDATE statements, a list of column names which should be present in the VALUES clause of the compiled statement. If None, all columns from the target table object are rendered.
dialect – A Dialect instance from which a Compiled will be acquired. This argument takes precedence over the bind argument as well as this ClauseElement’s bound engine, if any.
inline – Used for INSERT statements, for a dialect which does not support inline retrieval of newly generated primary key columns, will force the expression used to create the new primary key value to be rendered inline within the INSERT statement’s VALUES clause. This typically refers to Sequence execution but may also refer to any server-side default generation function associated with a primary key Column.
compile_kwargs –
optional dictionary of additional parameters that will be passed through to the compiler within all “visit” methods. This allows any custom flag to be passed through to a custom compilation construct, for example. It is also used for the case of passing the literal_binds flag through:
```
from sqlalchemy.sql import table, column, select

t = table('t', column('x'))

s = select([t]).where(t.c.x == 5)

print s.compile(compile_kwargs={"literal_binds": True})
```
New in version 0.9.0.

method sqlalchemy.schema.Table.correspond_on_equivalents(column, equivalents)¶: inherited from the FromClause.correspond_on_equivalents() method of FromClause

Return corresponding_column for the given column, or if None search for a match in the given dictionary.

method sqlalchemy.schema.Table.corresponding_column(column, require_embedded=False)¶

inherited from the FromClause.corresponding_column() method of FromClause

Given a ColumnElement, return the exported ColumnElement object from this Selectable which corresponds to that original Column via a common ancestor column.

Parameters:

column – the target ColumnElement to be matched
require_embedded – only return corresponding columns for the given ColumnElement, if the given ColumnElement is actually present within a sub-element of this FromClause. Normally the column will match if it merely shares a common ancestor with one of the exported columns of this FromClause.

method sqlalchemy.schema.Table.count(functions, whereclause=None, **params)¶: inherited from the FromClause.count() method of FromClause

return a SELECT COUNT generated against this FromClause.

Deprecated since version 1.1: The FromClause.count() method is deprecated, and will be removed in a future release. Please use the count function available from the func namespace.

See also

count

method sqlalchemy.schema.Table.create(bind=None, checkfirst=False)¶: Issue a CREATE statement for this Table, using the given Connectable for connectivity.

See also

MetaData.create_all().

method sqlalchemy.schema.Table.delete(dml, whereclause=None, **kwargs)¶

inherited from the TableClause.delete() method of TableClause

Generate a delete() construct against this TableClause.

E.g.:

table.delete().where(table.c.id==7)

See delete() for argument and usage information.

attribute sqlalchemy.schema.Table.description¶: inherited from the TableClause.description attribute of TableClause

attribute sqlalchemy.schema.Table.dialect_kwargs¶

inherited from the DialectKWArgs.dialect_kwargs attribute of DialectKWArgs

A collection of keyword arguments specified as dialect-specific options to this construct.

The arguments are present here in their original <dialect>_<kwarg> format. Only arguments that were actually passed are included; unlike the DialectKWArgs.dialect_options collection, which contains all options known by this dialect including defaults.

The collection is also writable; keys are accepted of the form <dialect>_<kwarg> where the value will be assembled into the list of options.

New in version 0.9.2.

Changed in version 0.9.4: The DialectKWArgs.dialect_kwargs collection is now writable.

See also

DialectKWArgs.dialect_options - nested dictionary form

attribute sqlalchemy.schema.Table.dialect_options¶

inherited from the DialectKWArgs.dialect_options attribute of DialectKWArgs

A collection of keyword arguments specified as dialect-specific options to this construct.

This is a two-level nested registry, keyed to <dialect_name> and <argument_name>. For example, the postgresql_where argument would be locatable as:

arg = my_object.dialect_options['postgresql']['where']

New in version 0.9.2.

See also

DialectKWArgs.dialect_kwargs - flat dictionary form

method sqlalchemy.schema.Table.drop(bind=None, checkfirst=False)¶: Issue a DROP statement for this Table, using the given Connectable for connectivity.

See also

MetaData.drop_all().

method sqlalchemy.schema.Table.exists(bind=None)¶: Return True if this table exists.

attribute sqlalchemy.schema.Table.foreign_key_constraints¶

ForeignKeyConstraint objects referred to by this Table.

This list is produced from the collection of ForeignKey objects currently associated.

New in version 1.0.0.

attribute sqlalchemy.schema.Table.foreign_keys¶: inherited from the FromClause.foreign_keys attribute of FromClause

Return the collection of ForeignKey objects which this FromClause references.

method sqlalchemy.schema.Table.get_children(column_collections=True, schema_visitor=False, **kw)¶: used to allow SchemaVisitor access

attribute sqlalchemy.schema.Table.implicit_returning = False¶: inherited from the TableClause.implicit_returning attribute of TableClause

TableClause doesn’t support having a primary key or column -level defaults, so implicit returning doesn’t apply.

attribute sqlalchemy.schema.Table.info¶

inherited from the SchemaItem.info attribute of SchemaItem

Info dictionary associated with the object, allowing user-defined data to be associated with this SchemaItem.

The dictionary is automatically generated when first accessed. It can also be specified in the constructor of some objects, such as Table and Column.

method sqlalchemy.schema.Table.insert(dml, values=None, inline=False, **kwargs)¶

inherited from the TableClause.insert() method of TableClause

Generate an insert() construct against this TableClause.

E.g.:

table.insert().values(name='foo')

See insert() for argument and usage information.

method sqlalchemy.schema.Table.is_derived_from(fromclause)¶

inherited from the FromClause.is_derived_from() method of FromClause

Return True if this FromClause is ‘derived’ from the given FromClause.

An example would be an Alias of a Table is derived from that Table.

method sqlalchemy.schema.Table.join(right, onclause=None, isouter=False, full=False)¶

inherited from the FromClause.join() method of FromClause

Return a Join from this FromClause to another FromClause.

E.g.:

from sqlalchemy import join

j = user_table.join(address_table,
                user_table.c.id == address_table.c.user_id)
stmt = select([user_table]).select_from(j)

would emit SQL along the lines of:

SELECT user.id, user.name FROM user
JOIN address ON user.id = address.user_id

Parameters:

right – the right side of the join; this is any FromClause object such as a Table object, and may also be a selectable-compatible object such as an ORM-mapped class.
onclause – a SQL expression representing the ON clause of the join. If left at None, FromClause.join() will attempt to join the two tables based on a foreign key relationship.
isouter – if True, render a LEFT OUTER JOIN, instead of JOIN.
full –
if True, render a FULL OUTER JOIN, instead of LEFT OUTER JOIN. Implies FromClause.join.isouter.

New in version 1.1.

See also

join() - standalone function

Join - the type of object produced

attribute sqlalchemy.schema.Table.key¶

Return the ‘key’ for this Table.

This value is used as the dictionary key within the MetaData.tables collection. It is typically the same as that of Table.name for a table with no Table.schema set; otherwise it is typically of the form schemaname.tablename.

attribute sqlalchemy.schema.Table.kwargs¶: inherited from the DialectKWArgs.kwargs attribute of DialectKWArgs

A synonym for DialectKWArgs.dialect_kwargs.

method sqlalchemy.schema.Table.lateral(name=None)¶

inherited from the FromClause.lateral() method of FromClause

Return a LATERAL alias of this FromClause.

The return value is the Lateral construct also provided by the top-level lateral() function.

New in version 1.1.

See also

LATERAL correlation - overview of usage.

method sqlalchemy.schema.Table.outerjoin(right, onclause=None, full=False)¶

inherited from the FromClause.outerjoin() method of FromClause

Return a Join from this FromClause to another FromClause, with the “isouter” flag set to True.

E.g.:

from sqlalchemy import outerjoin

j = user_table.outerjoin(address_table,
                user_table.c.id == address_table.c.user_id)

The above is equivalent to:

j = user_table.join(
    address_table,
    user_table.c.id == address_table.c.user_id,
    isouter=True)

Parameters:

right – the right side of the join; this is any FromClause object such as a Table object, and may also be a selectable-compatible object such as an ORM-mapped class.
onclause – a SQL expression representing the ON clause of the join. If left at None, FromClause.join() will attempt to join the two tables based on a foreign key relationship.
full –
if True, render a FULL OUTER JOIN, instead of LEFT OUTER JOIN.

New in version 1.1.

See also

FromClause.join()

Join

method sqlalchemy.schema.Table.params(*optionaldict, **kwargs)¶

inherited from the Immutable.params() method of Immutable

Return a copy with bindparam() elements replaced.

Returns a copy of this ClauseElement with bindparam() elements replaced with values taken from the given dictionary:

>>> clause = column('x') + bindparam('foo')
>>> print clause.compile().params
{'foo':None}
>>> print clause.params({'foo':7}).compile().params
{'foo':7}

attribute sqlalchemy.schema.Table.primary_key¶: inherited from the FromClause.primary_key attribute of FromClause

Return the collection of Column objects which comprise the primary key of this FromClause.

attribute sqlalchemy.schema.Table.quote¶: inherited from the SchemaItem.quote attribute of SchemaItem

Return the value of the quote flag passed to this schema object, for those schema items which have a name field.

Deprecated since version 0.9: The SchemaItem.quote attribute is deprecated and will be removed in a future release. Use the quoted_name.quote attribute on the name field of the target schema item to retrievequoted status.

attribute sqlalchemy.schema.Table.quote_schema¶: Return the value of the quote_schema flag passed to this Table.

Deprecated since version 0.9: The SchemaItem.quote() method is deprecated and will be removed in a future release. Use the quoted_name.quote attribute on the schema field of the target schema item to retrieve quoted status.

method sqlalchemy.schema.Table.replace_selectable(sqlutil, old, alias)¶: inherited from the FromClause.replace_selectable() method of FromClause

replace all occurrences of FromClause ‘old’ with the given Alias object, returning a copy of this FromClause.

attribute sqlalchemy.schema.Table.schema = None¶

inherited from the FromClause.schema attribute of FromClause

Define the ‘schema’ attribute for this FromClause.

This is typically None for most objects except that of Table, where it is taken as the value of the Table.schema argument.

method sqlalchemy.schema.Table.select(whereclause=None, **params)¶: inherited from the FromClause.select() method of FromClause

return a SELECT of this FromClause.

See also

select() - general purpose method which allows for arbitrary column lists.

method sqlalchemy.schema.Table.self_group(against=None)¶

inherited from the ClauseElement.self_group() method of ClauseElement

Apply a ‘grouping’ to this ClauseElement.

This method is overridden by subclasses to return a “grouping” construct, i.e. parenthesis. In particular it’s used by “binary” expressions to provide a grouping around themselves when placed into a larger expression, as well as by select() constructs when placed into the FROM clause of another select(). (Note that subqueries should be normally created using the Select.alias() method, as many platforms require nested SELECT statements to be named).

As expressions are composed together, the application of self_group() is automatic - end-user code should never need to use this method directly. Note that SQLAlchemy’s clause constructs take operator precedence into account - so parenthesis might not be needed, for example, in an expression like x OR (y AND z) - AND takes precedence over OR.

The base self_group() method of ClauseElement just returns self.

method sqlalchemy.schema.Table.tablesample(sampling, name=None, seed=None)¶

inherited from the FromClause.tablesample() method of FromClause

Return a TABLESAMPLE alias of this FromClause.

The return value is the TableSample construct also provided by the top-level tablesample() function.

New in version 1.1.

See also

tablesample() - usage guidelines and parameters

method sqlalchemy.schema.Table.tometadata(metadata, schema=symbol('retain_schema'), referred_schema_fn=None, name=None)¶

Return a copy of this Table associated with a different MetaData.

E.g.:

m1 = MetaData()

user = Table('user', m1, Column('id', Integer, primary_key=True))

m2 = MetaData()
user_copy = user.tometadata(m2)

Parameters:

metadata – Target MetaData object, into which the new Table object will be created.
schema –
optional string name indicating the target schema. Defaults to the special symbol RETAIN_SCHEMA which indicates that no change to the schema name should be made in the new Table. If set to a string name, the new Table will have this new name as the .schema. If set to None, the schema will be set to that of the schema set on the target MetaData, which is typically None as well, unless set explicitly:
```
m2 = MetaData(schema='newschema')

# user_copy_one will have "newschema" as the schema name
user_copy_one = user.tometadata(m2, schema=None)

m3 = MetaData()  # schema defaults to None

# user_copy_two will have None as the schema name
user_copy_two = user.tometadata(m3, schema=None)
```
referred_schema_fn –
optional callable which can be supplied in order to provide for the schema name that should be assigned to the referenced table of a ForeignKeyConstraint. The callable accepts this parent Table, the target schema that we are changing to, the ForeignKeyConstraint object, and the existing “target schema” of that constraint. The function should return the string schema name that should be applied. E.g.:
```
def referred_schema_fn(table, to_schema,
                                constraint, referred_schema):
    if referred_schema == 'base_tables':
        return referred_schema
    else:
        return to_schema

new_table = table.tometadata(m2, schema="alt_schema",
                        referred_schema_fn=referred_schema_fn)
```
New in version 0.9.2.
name –
optional string name indicating the target table name. If not specified or None, the table name is retained. This allows a Table to be copied to the same MetaData target with a new name.

New in version 1.0.0.

method sqlalchemy.schema.Table.unique_params(*optionaldict, **kwargs)¶

inherited from the Immutable.unique_params() method of Immutable

Return a copy with bindparam() elements replaced.

Same functionality as params(), except adds unique=True to affected bind parameters so that multiple statements can be used.

method sqlalchemy.schema.Table.update(dml, whereclause=None, values=None, inline=False, **kwargs)¶

inherited from the TableClause.update() method of TableClause

Generate an update() construct against this TableClause.

E.g.:

table.update().where(table.c.id==7).values(name='foo')

See update() for argument and usage information.

class sqlalchemy.schema.ThreadLocalMetaData¶

A MetaData variant that presents a different bind in every thread.

Makes the bind property of the MetaData a thread-local value, allowing this collection of tables to be bound to different Engine implementations or connections in each thread.

The ThreadLocalMetaData starts off bound to None in each thread. Binds must be made explicitly by assigning to the bind property or using connect(). You can also re-bind dynamically multiple times per thread, just like a regular MetaData.

Members

__init__(), bind, dispose(), is_bound()

Class signature

class sqlalchemy.schema.ThreadLocalMetaData (sqlalchemy.schema.MetaData)

method sqlalchemy.schema.ThreadLocalMetaData.__init__()¶: Construct a ThreadLocalMetaData.

attribute sqlalchemy.schema.ThreadLocalMetaData.bind¶

The bound Engine or Connection for this thread.

This property may be assigned an Engine or Connection, or assigned a string or URL to automatically create a basic Engine for this bind with create_engine().

method sqlalchemy.schema.ThreadLocalMetaData.dispose()¶: Dispose all bound engines, in all thread contexts.

method sqlalchemy.schema.ThreadLocalMetaData.is_bound()¶: True if there is a bind for this thread.

SQLAlchemy 1.2 Documentation

SQLAlchemy 1.2 Documentation

SQLAlchemy Core

Describing Databases with MetaData¶

Accessing Tables and Columns¶

Creating and Dropping Database Tables¶

Altering Schemas through Migrations¶

Specifying the Schema Name¶

Backend-Specific Options¶

Column, Table, MetaData API¶