Session API¶

Session and sessionmaker()¶

Object Name	Description
Session	Manages persistence operations for ORM-mapped objects.
sessionmaker	A configurable `Session` factory.
SessionTransaction	A `Session`-level transaction.

class sqlalchemy.orm.session.sessionmaker(bind=None, class_=<class 'sqlalchemy.orm.session.Session'>, autoflush=True, autocommit=False, expire_on_commit=True, info=None, **kw)¶

A configurable Session factory.

The sessionmaker factory generates new Session objects when called, creating them given the configurational arguments established here.

e.g.:

# global scope
Session = sessionmaker(autoflush=False)

# later, in a local scope, create and use a session:
sess = Session()

Any keyword arguments sent to the constructor itself will override the “configured” keywords:

Session = sessionmaker()

# bind an individual session to a connection
sess = Session(bind=connection)

The class also includes a method configure(), which can be used to specify additional keyword arguments to the factory, which will take effect for subsequent Session objects generated. This is usually used to associate one or more Engine objects with an existing sessionmaker factory before it is first used:

# application starts
Session = sessionmaker()

# ... later
engine = create_engine('sqlite:///foo.db')
Session.configure(bind=engine)

sess = Session()

Members

__call__(), __init__(), close_all(), configure(), identity_key(), object_session()

Class signature

class sqlalchemy.orm.session.sessionmaker (sqlalchemy.orm.session._SessionClassMethods)

method sqlalchemy.orm.session.sessionmaker.__call__(**local_kw)¶

Produce a new Session object using the configuration established in this sessionmaker.

In Python, the __call__ method is invoked on an object when it is “called” in the same way as a function:

Session = sessionmaker()
session = Session()  # invokes sessionmaker.__call__()

method sqlalchemy.orm.session.sessionmaker.__init__(bind=None, class_=<class 'sqlalchemy.orm.session.Session'>, autoflush=True, autocommit=False, expire_on_commit=True, info=None, **kw)¶

Construct a new sessionmaker.

All arguments here except for class_ correspond to arguments accepted by Session directly. See the Session.__init__() docstring for more details on parameters.

Parameters:

bind – a Engine or other Connectable with which newly created Session objects will be associated.
class_ – class to use in order to create new Session objects. Defaults to Session.
autoflush – The autoflush setting to use with newly created Session objects.
autocommit – The autocommit setting to use with newly created Session objects.
expire_on_commit=True – the expire_on_commit setting to use with newly created Session objects.
info –
optional dictionary of information that will be available via Session.info. Note this dictionary is updated, not replaced, when the info parameter is specified to the specific Session construction operation.

New in version 0.9.0.
**kw – all other keyword arguments are passed to the constructor of newly created Session objects.

classmethod sqlalchemy.orm.session.sessionmaker.close_all()¶: inherited from the sqlalchemy.orm.session._SessionClassMethods.close_all method of sqlalchemy.orm.session._SessionClassMethods

Close all sessions in memory.

method sqlalchemy.orm.session.sessionmaker.configure(**new_kw)¶

(Re)configure the arguments for this sessionmaker.

e.g.:

Session = sessionmaker()

Session.configure(bind=create_engine('sqlite://'))

classmethod sqlalchemy.orm.session.sessionmaker.identity_key(orm_util, *args, **kwargs)¶

inherited from the sqlalchemy.orm.session._SessionClassMethods.identity_key method of sqlalchemy.orm.session._SessionClassMethods

Return an identity key.

This is an alias of identity_key().

classmethod sqlalchemy.orm.session.sessionmaker.object_session(instance)¶

inherited from the sqlalchemy.orm.session._SessionClassMethods.object_session method of sqlalchemy.orm.session._SessionClassMethods

Return the Session to which an object belongs.

This is an alias of object_session().

class sqlalchemy.orm.session.Session(bind=None, autoflush=True, expire_on_commit=True, _enable_transaction_accounting=True, autocommit=False, twophase=False, weak_identity_map=True, binds=None, extension=None, enable_baked_queries=True, info=None, query_cls=<class 'sqlalchemy.orm.query.Query'>)¶

Manages persistence operations for ORM-mapped objects.

The Session’s usage paradigm is described at Using the Session.

Class signature

class sqlalchemy.orm.session.Session (sqlalchemy.orm.session._SessionClassMethods)

method sqlalchemy.orm.session.Session.__init__(bind=None, autoflush=True, expire_on_commit=True, _enable_transaction_accounting=True, autocommit=False, twophase=False, weak_identity_map=True, binds=None, extension=None, enable_baked_queries=True, info=None, query_cls=<class 'sqlalchemy.orm.query.Query'>)¶

Construct a new Session.

See also the sessionmaker function which is used to generate a Session-producing callable with a given set of arguments.

Parameters:

autocommit –

Warning

The autocommit flag is not for general use, and if it is used, queries should only be invoked within the span of a Session.begin() / Session.commit() pair. Executing queries outside of a demarcated transaction is a legacy mode of usage, and can in some cases lead to concurrent connection checkouts.

Defaults to False. When True, the Session does not keep a persistent transaction running, and will acquire connections from the engine on an as-needed basis, returning them immediately after their use. Flushes will begin and commit (or possibly rollback) their own transaction if no transaction is present. When using this mode, the Session.begin() method is used to explicitly start transactions.

See also

Autocommit Mode
autoflush – When True, all query operations will issue a Session.flush() call to this Session before proceeding. This is a convenience feature so that Session.flush() need not be called repeatedly in order for database queries to retrieve results. It’s typical that autoflush is used in conjunction with autocommit=False. In this scenario, explicit calls to Session.flush() are rarely needed; you usually only need to call Session.commit() (which flushes) to finalize changes.
bind – An optional Engine or Connection to which this Session should be bound. When specified, all SQL operations performed by this session will execute via this connectable.
binds –
A dictionary which may specify any number of Engine or Connection objects as the source of connectivity for SQL operations on a per-entity basis. The keys of the dictionary consist of any series of mapped classes, arbitrary Python classes that are bases for mapped classes, Table objects and Mapper objects. The values of the dictionary are then instances of Engine or less commonly Connection objects. Operations which proceed relative to a particular mapped class will consult this dictionary for the closest matching entity in order to determine which Engine should be used for a particular SQL operation. The complete heuristics for resolution are described at Session.get_bind(). Usage looks like:
```
Session = sessionmaker(binds={
    SomeMappedClass: create_engine('postgresql://engine1'),
    SomeDeclarativeBase: create_engine('postgresql://engine2'),
    some_mapper: create_engine('postgresql://engine3'),
    some_table: create_engine('postgresql://engine4'),
    })
```
See also

Partitioning Strategies (e.g. multiple database backends per Session)

Session.bind_mapper()

Session.bind_table()

Session.get_bind()
class_ – Specify an alternate class other than sqlalchemy.orm.session.Session which should be used by the returned class. This is the only argument that is local to the sessionmaker function, and is not sent directly to the constructor for Session.
enable_baked_queries –
defaults to True. A flag consumed by the sqlalchemy.ext.baked extension to determine if “baked queries” should be cached, as is the normal operation of this extension. When set to False, all caching is disabled, including baked queries defined by the calling application as well as those used internally. Setting this flag to False can significantly reduce memory use, however will also degrade performance for those areas that make use of baked queries (such as relationship loaders). Additionally, baked query logic in the calling application or potentially within the ORM that may be malfunctioning due to cache key collisions or similar can be flagged by observing if this flag resolves the issue.

New in version 1.2.
_enable_transaction_accounting –
Defaults to True. A legacy-only flag which when False disables all 0.5-style object accounting on transaction boundaries.

Deprecated since version 0.7: the Session._enable_transaction_accounting parameter will be removed in a future release.
expire_on_commit – Defaults to True. When True, all instances will be fully expired after each commit(), so that all attribute/object access subsequent to a completed transaction will load from the most recent database state.
extension –
An optional SessionExtension instance, or a list of such instances, which will receive pre- and post- commit and flush events, as well as a post-rollback event.

Deprecated since version 0.7: SessionExtension is deprecated in favor of the SessionEvents listener interface. The Session.extension parameter will be removed in a future release.
info –
optional dictionary of arbitrary data to be associated with this Session. Is available via the Session.info attribute. Note the dictionary is copied at construction time so that modifications to the per- Session dictionary will be local to that Session.

New in version 0.9.0.
query_cls – Class which should be used to create new Query objects, as returned by the Session.query() method. Defaults to Query.
twophase – When True, all transactions will be started as a “two phase” transaction, i.e. using the “two phase” semantics of the database in use along with an XID. During a commit(), after flush() has been issued for all attached databases, the TwoPhaseTransaction.prepare() method on each database’s TwoPhaseTransaction will be called. This allows each database to roll back the entire transaction, before each transaction is committed.
weak_identity_map –
Defaults to True - when set to False, objects placed in the Session will be strongly referenced until explicitly removed or the Session is closed.

Deprecated since version 1.0: The Session.weak_identity_map parameter as well as the strong-referencing identity map are deprecated, and will be removed in a future release. For the use case where objects present in a Session need to be automatically strong referenced, see the recipe at Session Referencing Behavior for an event-based approach to maintaining strong identity references.

method sqlalchemy.orm.session.Session.add(instance, _warn=True)¶

Place an object in the Session.

Its state will be persisted to the database on the next flush operation.

Repeated calls to add() will be ignored. The opposite of add() is expunge().

method sqlalchemy.orm.session.Session.add_all(instances)¶: Add the given collection of instances to this Session.

method sqlalchemy.orm.session.Session.begin(subtransactions=False, nested=False)¶

Begin a transaction on this Session.

Warning

The Session.begin() method is part of a larger pattern of use with the Session known as autocommit mode. This is essentially a legacy mode of use and is not necessary for new applications. The Session normally handles the work of “begin” transparently, which in turn relies upon the Python DBAPI to transparently “begin” transactions; there is no need to explicitly begin transactions when using modern Session programming patterns. In its default mode of autocommit=False, the Session does all of its work within the context of a transaction, so as soon as you call Session.commit(), the next transaction is implicitly started when the next database operation is invoked. See Autocommit Mode for further background.

The method will raise an error if this Session is already inside of a transaction, unless Session.begin.subtransactions or Session.begin.nested are specified. A “subtransaction” is essentially a code embedding pattern that does not affect the transactional state of the database connection unless a rollback is emitted, in which case the whole transaction is rolled back. For documentation on subtransactions, please see Using Subtransactions with Autocommit.

Parameters:

subtransactions – if True, indicates that this Session.begin() can create a “subtransaction”.
nested – if True, begins a SAVEPOINT transaction and is equivalent to calling Session.begin_nested(). For documentation on SAVEPOINT transactions, please see Using SAVEPOINT.

Returns:

the SessionTransaction object. Note that SessionTransaction acts as a Python context manager, allowing Session.begin() to be used in a “with” block. See Autocommit Mode for an example.

See also

Autocommit Mode

Session.begin_nested()

method sqlalchemy.orm.session.Session.begin_nested()¶

Begin a “nested” transaction on this Session, e.g. SAVEPOINT.

The target database(s) and associated drivers must support SQL SAVEPOINT for this method to function correctly.

For documentation on SAVEPOINT transactions, please see Using SAVEPOINT.

Returns:: the SessionTransaction object. Note that SessionTransaction acts as a context manager, allowing Session.begin_nested() to be used in a “with” block. See Using SAVEPOINT for a usage example.

See also

Using SAVEPOINT

Serializable isolation / Savepoints / Transactional DDL - special workarounds required with the SQLite driver in order for SAVEPOINT to work correctly.

method sqlalchemy.orm.session.Session.bind_mapper(mapper, bind)¶

Associate a Mapper or arbitrary Python class with a “bind”, e.g. an Engine or Connection.

The given entity is added to a lookup used by the Session.get_bind() method.

Parameters:

mapper – a Mapper object, or an instance of a mapped class, or any Python class that is the base of a set of mapped classes.
bind – an Engine or Connection object.

Session.binds

Session.bind_table()

method sqlalchemy.orm.session.Session.bind_table(table, bind)¶

Associate a Table with a “bind”, e.g. an Engine or Connection.

The given Table is added to a lookup used by the Session.get_bind() method.

Parameters:

table – a Table object, which is typically the target of an ORM mapping, or is present within a selectable that is mapped.
bind – an Engine or Connection object.

Session.binds

Session.bind_mapper()

method sqlalchemy.orm.session.Session.bulk_insert_mappings(mapper, mappings, return_defaults=False, render_nulls=False)¶

Perform a bulk insert of the given list of mapping dictionaries.

The bulk insert feature allows plain Python dictionaries to be used as the source of simple INSERT operations which can be more easily grouped together into higher performing “executemany” operations. Using dictionaries, there is no “history” or session state management features in use, reducing latency when inserting large numbers of simple rows.

The values within the dictionaries as given are typically passed without modification into Core Insert() constructs, after organizing the values within them across the tables to which the given mapper is mapped.

New in version 1.0.0.

Warning

The bulk insert feature allows for a lower-latency INSERT of rows at the expense of most other unit-of-work features. Features such as object management, relationship handling, and SQL clause support are silently omitted in favor of raw INSERT of records.

Please read the list of caveats at Bulk Operations before using this method, and fully test and confirm the functionality of all code developed using these systems.

Parameters:

mapper – a mapped class, or the actual Mapper object, representing the single kind of object represented within the mapping list.
mappings – a list of dictionaries, each one containing the state of the mapped row to be inserted, in terms of the attribute names on the mapped class. If the mapping refers to multiple tables, such as a joined-inheritance mapping, each dictionary must contain all keys to be populated into all tables.
return_defaults – when True, rows that are missing values which generate defaults, namely integer primary key defaults and sequences, will be inserted one at a time, so that the primary key value is available. In particular this will allow joined-inheritance and other multi-table mappings to insert correctly without the need to provide primary key values ahead of time; however, Session.bulk_insert_mappings.return_defaults greatly reduces the performance gains of the method overall. If the rows to be inserted only refer to a single table, then there is no reason this flag should be set as the returned default information is not used.
render_nulls –
When True, a value of None will result in a NULL value being included in the INSERT statement, rather than the column being omitted from the INSERT. This allows all the rows being INSERTed to have the identical set of columns which allows the full set of rows to be batched to the DBAPI. Normally, each column-set that contains a different combination of NULL values than the previous row must omit a different series of columns from the rendered INSERT statement, which means it must be emitted as a separate statement. By passing this flag, the full set of rows are guaranteed to be batchable into one batch; the cost however is that server-side defaults which are invoked by an omitted column will be skipped, so care must be taken to ensure that these are not necessary.

Warning

When this flag is set, server side default SQL values will not be invoked for those columns that are inserted as NULL; the NULL value will be sent explicitly. Care must be taken to ensure that no server-side default functions need to be invoked for the operation as a whole.

New in version 1.1.

See also

Bulk Operations

Session.bulk_save_objects()

Session.bulk_update_mappings()

method sqlalchemy.orm.session.Session.bulk_save_objects(objects, return_defaults=False, update_changed_only=True)¶

Perform a bulk save of the given list of objects.

The bulk save feature allows mapped objects to be used as the source of simple INSERT and UPDATE operations which can be more easily grouped together into higher performing “executemany” operations; the extraction of data from the objects is also performed using a lower-latency process that ignores whether or not attributes have actually been modified in the case of UPDATEs, and also ignores SQL expressions.

The objects as given are not added to the session and no additional state is established on them, unless the return_defaults flag is also set, in which case primary key attributes and server-side default values will be populated.

New in version 1.0.0.

Warning

The bulk save feature allows for a lower-latency INSERT/UPDATE of rows at the expense of most other unit-of-work features. Features such as object management, relationship handling, and SQL clause support are silently omitted in favor of raw INSERT/UPDATES of records.

Please read the list of caveats at Bulk Operations before using this method, and fully test and confirm the functionality of all code developed using these systems.

Parameters:

objects –
a list of mapped object instances. The mapped objects are persisted as is, and are not associated with the Session afterwards.

For each object, whether the object is sent as an INSERT or an UPDATE is dependent on the same rules used by the Session in traditional operation; if the object has the InstanceState.key attribute set, then the object is assumed to be “detached” and will result in an UPDATE. Otherwise, an INSERT is used.

In the case of an UPDATE, statements are grouped based on which attributes have changed, and are thus to be the subject of each SET clause. If update_changed_only is False, then all attributes present within each object are applied to the UPDATE statement, which may help in allowing the statements to be grouped together into a larger executemany(), and will also reduce the overhead of checking history on attributes.
return_defaults – when True, rows that are missing values which generate defaults, namely integer primary key defaults and sequences, will be inserted one at a time, so that the primary key value is available. In particular this will allow joined-inheritance and other multi-table mappings to insert correctly without the need to provide primary key values ahead of time; however, Session.bulk_save_objects.return_defaults greatly reduces the performance gains of the method overall.
update_changed_only – when True, UPDATE statements are rendered based on those attributes in each state that have logged changes. When False, all attributes present are rendered into the SET clause with the exception of primary key attributes.

See also

Bulk Operations

Session.bulk_insert_mappings()

Session.bulk_update_mappings()

method sqlalchemy.orm.session.Session.bulk_update_mappings(mapper, mappings)¶

Perform a bulk update of the given list of mapping dictionaries.

The bulk update feature allows plain Python dictionaries to be used as the source of simple UPDATE operations which can be more easily grouped together into higher performing “executemany” operations. Using dictionaries, there is no “history” or session state management features in use, reducing latency when updating large numbers of simple rows.

New in version 1.0.0.

Warning

The bulk update feature allows for a lower-latency UPDATE of rows at the expense of most other unit-of-work features. Features such as object management, relationship handling, and SQL clause support are silently omitted in favor of raw UPDATES of records.

Please read the list of caveats at Bulk Operations before using this method, and fully test and confirm the functionality of all code developed using these systems.

Parameters:

mapper – a mapped class, or the actual Mapper object, representing the single kind of object represented within the mapping list.
mappings – a list of dictionaries, each one containing the state of the mapped row to be updated, in terms of the attribute names on the mapped class. If the mapping refers to multiple tables, such as a joined-inheritance mapping, each dictionary may contain keys corresponding to all tables. All those keys which are present and are not part of the primary key are applied to the SET clause of the UPDATE statement; the primary key values, which are required, are applied to the WHERE clause.

See also

Bulk Operations

Session.bulk_insert_mappings()

Session.bulk_save_objects()

method sqlalchemy.orm.session.Session.close()¶

Close this Session.

This clears all items and ends any transaction in progress.

If this session were created with autocommit=False, a new transaction is immediately begun. Note that this new transaction does not use any connection resources until they are first needed.

classmethod sqlalchemy.orm.session.Session.close_all()¶: inherited from the sqlalchemy.orm.session._SessionClassMethods.close_all method of sqlalchemy.orm.session._SessionClassMethods

Close all sessions in memory.

method sqlalchemy.orm.session.Session.commit()¶

Flush pending changes and commit the current transaction.

If no transaction is in progress, this method raises an InvalidRequestError.

By default, the Session also expires all database loaded state on all ORM-managed attributes after transaction commit. This so that subsequent operations load the most recent data from the database. This behavior can be disabled using the expire_on_commit=False option to sessionmaker or the Session constructor.

If a subtransaction is in effect (which occurs when begin() is called multiple times), the subtransaction will be closed, and the next call to commit() will operate on the enclosing transaction.

When using the Session in its default mode of autocommit=False, a new transaction will be begun immediately after the commit, but note that the newly begun transaction does not use any connection resources until the first SQL is actually emitted.

See also

Committing

method sqlalchemy.orm.session.Session.connection(mapper=None, clause=None, bind=None, close_with_result=False, execution_options=None, **kw)¶

Return a Connection object corresponding to this Session object’s transactional state.

If this Session is configured with autocommit=False, either the Connection corresponding to the current transaction is returned, or if no transaction is in progress, a new one is begun and the Connection returned (note that no transactional state is established with the DBAPI until the first SQL statement is emitted).

Alternatively, if this Session is configured with autocommit=True, an ad-hoc Connection is returned using Engine.contextual_connect() on the underlying Engine.

Ambiguity in multi-bind or unbound Session objects can be resolved through any of the optional keyword arguments. This ultimately makes usage of the get_bind() method for resolution.

Parameters:

bind – Optional Engine to be used as the bind. If this engine is already involved in an ongoing transaction, that connection will be used. This argument takes precedence over mapper, clause.
mapper – Optional mapper() mapped class, used to identify the appropriate bind. This argument takes precedence over clause.
clause – A ClauseElement (i.e. select(), text(), etc.) which will be used to locate a bind, if a bind cannot otherwise be identified.
close_with_result – Passed to Engine.connect(), indicating the Connection should be considered “single use”, automatically closing when the first result set is closed. This flag only has an effect if this Session is configured with autocommit=True and does not already have a transaction in progress.
execution_options –
a dictionary of execution options that will be passed to Connection.execution_options(), when the connection is first procured only. If the connection is already present within the Session, a warning is emitted and the arguments are ignored.

New in version 0.9.9.

See also

Setting Transaction Isolation Levels
**kw – Additional keyword arguments are sent to get_bind(), allowing additional arguments to be passed to custom implementations of get_bind().

method sqlalchemy.orm.session.Session.delete(instance)¶

Mark an instance as deleted.

The database delete operation occurs upon flush().

attribute sqlalchemy.orm.session.Session.deleted¶: The set of all instances marked as ‘deleted’ within this Session

attribute sqlalchemy.orm.session.Session.dirty¶

The set of all persistent instances considered dirty.

E.g.:

some_mapped_object in session.dirty

Instances are considered dirty when they were modified but not deleted.

Note that this ‘dirty’ calculation is ‘optimistic’; most attribute-setting or collection modification operations will mark an instance as ‘dirty’ and place it in this set, even if there is no net change to the attribute’s value. At flush time, the value of each attribute is compared to its previously saved value, and if there’s no net change, no SQL operation will occur (this is a more expensive operation so it’s only done at flush time).

To check if an instance has actionable net changes to its attributes, use the Session.is_modified() method.

method sqlalchemy.orm.session.Session.enable_relationship_loading(obj)¶

Associate an object with this Session for related object loading.

Warning

enable_relationship_loading() exists to serve special use cases and is not recommended for general use.

Accesses of attributes mapped with relationship() will attempt to load a value from the database using this Session as the source of connectivity. The values will be loaded based on foreign key and primary key values present on this object - if not present, then those relationships will be unavailable.

The object will be attached to this session, but will not participate in any persistence operations; its state for almost all purposes will remain either “transient” or “detached”, except for the case of relationship loading.

Also note that backrefs will often not work as expected. Altering a relationship-bound attribute on the target object may not fire off a backref event, if the effective value is what was already loaded from a foreign-key-holding value.

The Session.enable_relationship_loading() method is similar to the load_on_pending flag on relationship(). Unlike that flag, Session.enable_relationship_loading() allows an object to remain transient while still being able to load related items.

To make a transient object associated with a Session via Session.enable_relationship_loading() pending, add it to the Session using Session.add() normally. If the object instead represents an existing identity in the database, it should be merged using Session.merge().

Session.enable_relationship_loading() does not improve behavior when the ORM is used normally - object references should be constructed at the object level, not at the foreign key level, so that they are present in an ordinary way before flush() proceeds. This method is not intended for general use.

See also

load_on_pending at relationship() - this flag allows per-relationship loading of many-to-ones on items that are pending.

make_transient_to_detached() - allows for an object to be added to a Session without SQL emitted, which then will unexpire attributes on access.

method sqlalchemy.orm.session.Session.execute(clause, params=None, mapper=None, bind=None, **kw)¶

Execute a SQL expression construct or string statement within the current transaction.

Returns a ResultProxy representing results of the statement execution, in the same manner as that of an Engine or Connection.

E.g.:

result = session.execute(
            user_table.select().where(user_table.c.id == 5)
        )

Session.execute() accepts any executable clause construct, such as select(), insert(), update(), delete(), and text(). Plain SQL strings can be passed as well, which in the case of Session.execute() only will be interpreted the same as if it were passed via a text() construct. That is, the following usage:

result = session.execute(
            "SELECT * FROM user WHERE id=:param",
            {"param":5}
        )

is equivalent to:

from sqlalchemy import text
result = session.execute(
            text("SELECT * FROM user WHERE id=:param"),
            {"param":5}
        )

The second positional argument to Session.execute() is an optional parameter set. Similar to that of Connection.execute(), whether this is passed as a single dictionary, or a list of dictionaries, determines whether the DBAPI cursor’s execute() or executemany() is used to execute the statement. An INSERT construct may be invoked for a single row:

result = session.execute(
    users.insert(), {"id": 7, "name": "somename"})

or for multiple rows:

result = session.execute(users.insert(), [
                        {"id": 7, "name": "somename7"},
                        {"id": 8, "name": "somename8"},
                        {"id": 9, "name": "somename9"}
                    ])

The statement is executed within the current transactional context of this Session. The Connection which is used to execute the statement can also be acquired directly by calling the Session.connection() method. Both methods use a rule-based resolution scheme in order to determine the Connection, which in the average case is derived directly from the “bind” of the Session itself, and in other cases can be based on the mapper() and Table objects passed to the method; see the documentation for Session.get_bind() for a full description of this scheme.

The Session.execute() method does not invoke autoflush.

The ResultProxy returned by the Session.execute() method is returned with the “close_with_result” flag set to true; the significance of this flag is that if this Session is autocommitting and does not have a transaction-dedicated Connection available, a temporary Connection is established for the statement execution, which is closed (meaning, returned to the connection pool) when the ResultProxy has consumed all available data. This applies only when the Session is configured with autocommit=True and no transaction has been started.

Parameters:

clause – An executable statement (i.e. an Executable expression such as select()) or string SQL statement to be executed.
params – Optional dictionary, or list of dictionaries, containing bound parameter values. If a single dictionary, single-row execution occurs; if a list of dictionaries, an “executemany” will be invoked. The keys in each dictionary must correspond to parameter names present in the statement.
mapper – Optional mapper() or mapped class, used to identify the appropriate bind. This argument takes precedence over clause when locating a bind. See Session.get_bind() for more details.
bind – Optional Engine to be used as the bind. If this engine is already involved in an ongoing transaction, that connection will be used. This argument takes precedence over mapper and clause when locating a bind.
**kw – Additional keyword arguments are sent to Session.get_bind() to allow extensibility of “bind” schemes.

See also

SQL Expression Language Tutorial - Tutorial on using Core SQL constructs.

Working with Engines and Connections - Further information on direct statement execution.

Connection.execute() - core level statement execution method, which is Session.execute() ultimately uses in order to execute the statement.

method sqlalchemy.orm.session.Session.expire(instance, attribute_names=None)¶

Expire the attributes on an instance.

Marks the attributes of an instance as out of date. When an expired attribute is next accessed, a query will be issued to the Session object’s current transactional context in order to load all expired attributes for the given instance. Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction.

To expire all objects in the Session simultaneously, use Session.expire_all().

The Session object’s default behavior is to expire all state whenever the Session.rollback() or Session.commit() methods are called, so that new state can be loaded for the new transaction. For this reason, calling Session.expire() only makes sense for the specific case that a non-ORM SQL statement was emitted in the current transaction.

Parameters:

instance – The instance to be refreshed.
attribute_names – optional list of string attribute names indicating a subset of attributes to be expired.

See also

Refreshing / Expiring - introductory material

Session.expire()

Session.refresh()

method sqlalchemy.orm.session.Session.expire_all()¶

Expires all persistent instances within this Session.

When any attributes on a persistent instance is next accessed, a query will be issued using the Session object’s current transactional context in order to load all expired attributes for the given instance. Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction.

To expire individual objects and individual attributes on those objects, use Session.expire().

The Session object’s default behavior is to expire all state whenever the Session.rollback() or Session.commit() methods are called, so that new state can be loaded for the new transaction. For this reason, calling Session.expire_all() should not be needed when autocommit is False, assuming the transaction is isolated.

See also

Refreshing / Expiring - introductory material

Session.expire()

Session.refresh()

method sqlalchemy.orm.session.Session.expunge(instance)¶

Remove the instance from this Session.

This will free all internal references to the instance. Cascading will be applied according to the expunge cascade rule.

method sqlalchemy.orm.session.Session.expunge_all()¶

Remove all object instances from this Session.

This is equivalent to calling expunge(obj) on all objects in this Session.

method sqlalchemy.orm.session.Session.flush(objects=None)¶

Flush all the object changes to the database.

Writes out all pending object creations, deletions and modifications to the database as INSERTs, DELETEs, UPDATEs, etc. Operations are automatically ordered by the Session’s unit of work dependency solver.

Database operations will be issued in the current transactional context and do not affect the state of the transaction, unless an error occurs, in which case the entire transaction is rolled back. You may flush() as often as you like within a transaction to move changes from Python to the database’s transaction buffer.

For autocommit Sessions with no active manual transaction, flush() will create a transaction on the fly that surrounds the entire set of operations into the flush.

Parameters:

objects –

Optional; restricts the flush operation to operate only on elements that are in the given collection.

This feature is for an extremely narrow set of use cases where particular objects may need to be operated upon before the full flush() occurs. It is not intended for general use.

method sqlalchemy.orm.session.Session.get_bind(mapper=None, clause=None)¶

Return a “bind” to which this Session is bound.

The “bind” is usually an instance of Engine, except in the case where the Session has been explicitly bound directly to a Connection.

For a multiply-bound or unbound Session, the mapper or clause arguments are used to determine the appropriate bind to return.

Note that the “mapper” argument is usually present when Session.get_bind() is called via an ORM operation such as a Session.query(), each individual INSERT/UPDATE/DELETE operation within a Session.flush(), call, etc.

The order of resolution is:

if mapper given and session.binds is present, locate a bind based first on the mapper in use, then on the mapped class in use, then on any base classes that are present in the __mro__ of the mapped class, from more specific superclasses to more general.
if clause given and session.binds is present, locate a bind based on Table objects found in the given clause present in session.binds.
if session.bind is present, return that.
if clause given, attempt to return a bind linked to the MetaData ultimately associated with the clause.
if mapper given, attempt to return a bind linked to the MetaData ultimately associated with the Table or other selectable to which the mapper is mapped.
No bind can be found, UnboundExecutionError is raised.

Note that the Session.get_bind() method can be overridden on a user-defined subclass of Session to provide any kind of bind resolution scheme. See the example at Custom Vertical Partitioning.

Parameters:

mapper – Optional mapper() mapped class or instance of Mapper. The bind can be derived from a Mapper first by consulting the “binds” map associated with this Session, and secondly by consulting the MetaData associated with the Table to which the Mapper is mapped for a bind.
clause – A ClauseElement (i.e. select(), text(), etc.). If the mapper argument is not present or could not produce a bind, the given expression construct will be searched for a bound element, typically a Table associated with bound MetaData.

Session.binds

Session.bind_mapper()

Session.bind_table()

classmethod sqlalchemy.orm.session.Session.identity_key(orm_util, *args, **kwargs)¶

inherited from the sqlalchemy.orm.session._SessionClassMethods.identity_key method of sqlalchemy.orm.session._SessionClassMethods

Return an identity key.

This is an alias of identity_key().

attribute sqlalchemy.orm.session.Session.identity_map = None¶

A mapping of object identities to objects themselves.

Iterating through Session.identity_map.values() provides access to the full set of persistent objects (i.e., those that have row identity) currently in the session.

See also

identity_key() - helper function to produce the keys used in this dictionary.

attribute sqlalchemy.orm.session.Session.info¶

A user-modifiable dictionary.

The initial value of this dictionary can be populated using the info argument to the Session constructor or sessionmaker constructor or factory methods. The dictionary here is always local to this Session and can be modified independently of all other Session objects.

New in version 0.9.0.

method sqlalchemy.orm.session.Session.invalidate()¶

Close this Session, using connection invalidation.

This is a variant of Session.close() that will additionally ensure that the Connection.invalidate() method will be called on all Connection objects. This can be called when the database is known to be in a state where the connections are no longer safe to be used.

E.g.:

try:
    sess = Session()
    sess.add(User())
    sess.commit()
except gevent.Timeout:
    sess.invalidate()
    raise
except:
    sess.rollback()
    raise

This clears all items and ends any transaction in progress.

If this session were created with autocommit=False, a new transaction is immediately begun. Note that this new transaction does not use any connection resources until they are first needed.

New in version 0.9.9.

attribute sqlalchemy.orm.session.Session.is_active¶

True if this Session is in “transaction mode” and is not in “partial rollback” state.

The Session in its default mode of autocommit=False is essentially always in “transaction mode”, in that a SessionTransaction is associated with it as soon as it is instantiated. This SessionTransaction is immediately replaced with a new one as soon as it is ended, due to a rollback, commit, or close operation.

“Transaction mode” does not indicate whether or not actual database connection resources are in use; the SessionTransaction object coordinates among zero or more actual database transactions, and starts out with none, accumulating individual DBAPI connections as different data sources are used within its scope. The best way to track when a particular Session has actually begun to use DBAPI resources is to implement a listener using the SessionEvents.after_begin() method, which will deliver both the Session as well as the target Connection to a user-defined event listener.

The “partial rollback” state refers to when an “inner” transaction, typically used during a flush, encounters an error and emits a rollback of the DBAPI connection. At this point, the Session is in “partial rollback” and awaits for the user to call Session.rollback(), in order to close out the transaction stack. It is in this “partial rollback” period that the is_active flag returns False. After the call to Session.rollback(), the SessionTransaction is replaced with a new one and is_active returns True again.

When a Session is used in autocommit=True mode, the SessionTransaction is only instantiated within the scope of a flush call, or when Session.begin() is called. So is_active will always be False outside of a flush or Session.begin() block in this mode, and will be True within the Session.begin() block as long as it doesn’t enter “partial rollback” state.

From all the above, it follows that the only purpose to this flag is for application frameworks that wish to detect is a “rollback” is necessary within a generic error handling routine, for Session objects that would otherwise be in “partial rollback” mode. In a typical integration case, this is also not necessary as it is standard practice to emit Session.rollback() unconditionally within the outermost exception catch.

To track the transactional state of a Session fully, use event listeners, primarily the SessionEvents.after_begin(), SessionEvents.after_commit(), SessionEvents.after_rollback() and related events.

method sqlalchemy.orm.session.Session.is_modified(instance, include_collections=True, passive=True)¶

Return True if the given instance has locally modified attributes.

This method retrieves the history for each instrumented attribute on the instance and performs a comparison of the current value to its previously committed value, if any.

It is in effect a more expensive and accurate version of checking for the given instance in the Session.dirty collection; a full test for each attribute’s net “dirty” status is performed.

E.g.:

return session.is_modified(someobject)

A few caveats to this method apply:

Instances present in the Session.dirty collection may report False when tested with this method. This is because the object may have received change events via attribute mutation, thus placing it in Session.dirty, but ultimately the state is the same as that loaded from the database, resulting in no net change here.
Scalar attributes may not have recorded the previously set value when a new value was applied, if the attribute was not loaded, or was expired, at the time the new value was received - in these cases, the attribute is assumed to have a change, even if there is ultimately no net change against its database value. SQLAlchemy in most cases does not need the “old” value when a set event occurs, so it skips the expense of a SQL call if the old value isn’t present, based on the assumption that an UPDATE of the scalar value is usually needed, and in those few cases where it isn’t, is less expensive on average than issuing a defensive SELECT.

The “old” value is fetched unconditionally upon set only if the attribute container has the active_history flag set to True. This flag is set typically for primary key attributes and scalar object references that are not a simple many-to-one. To set this flag for any arbitrary mapped column, use the active_history argument with column_property().

Parameters:

instance – mapped instance to be tested for pending changes.
include_collections – Indicates if multivalued collections should be included in the operation. Setting this to False is a way to detect only local-column based properties (i.e. scalar columns or many-to-one foreign keys) that would result in an UPDATE for this instance upon flush.
passive –

Deprecated since version 0.8: The passive flag is deprecated and will be removed in a future release. The flag is no longer used and is ignored.

method sqlalchemy.orm.session.Session.merge(instance, load=True)¶

Copy the state of a given instance into a corresponding instance within this Session.

Session.merge() examines the primary key attributes of the source instance, and attempts to reconcile it with an instance of the same primary key in the session. If not found locally, it attempts to load the object from the database based on primary key, and if none can be located, creates a new instance. The state of each attribute on the source instance is then copied to the target instance. The resulting target instance is then returned by the method; the original source instance is left unmodified, and un-associated with the Session if not already.

This operation cascades to associated instances if the association is mapped with cascade="merge".

See Merging for a detailed discussion of merging.

Changed in version 1.1: - Session.merge() will now reconcile pending objects with overlapping primary keys in the same way as persistent. See Session.merge resolves pending conflicts the same as persistent for discussion.

Parameters:

instance – Instance to be merged.
load –
Boolean, when False, merge() switches into a “high performance” mode which causes it to forego emitting history events as well as all database access. This flag is used for cases such as transferring graphs of objects into a Session from a second level cache, or to transfer just-loaded objects into the Session owned by a worker thread or process without re-querying the database.

The load=False use case adds the caveat that the given object has to be in a “clean” state, that is, has no pending changes to be flushed - even if the incoming object is detached from any Session. This is so that when the merge operation populates local attributes and cascades to related objects and collections, the values can be “stamped” onto the target object as is, without generating any history or attribute events, and without the need to reconcile the incoming data with any existing related objects or collections that might not be loaded. The resulting objects from load=False are always produced as “clean”, so it is only appropriate that the given objects should be “clean” as well, else this suggests a mis-use of the method.

See also

make_transient_to_detached() - provides for an alternative means of “merging” a single object into the Session

attribute sqlalchemy.orm.session.Session.new¶: The set of all instances marked as ‘new’ within this Session.

attribute sqlalchemy.orm.session.Session.no_autoflush¶

Return a context manager that disables autoflush.

e.g.:

with session.no_autoflush:

    some_object = SomeClass()
    session.add(some_object)
    # won't autoflush
    some_object.related_thing = session.query(SomeRelated).first()

Operations that proceed within the with: block will not be subject to flushes occurring upon query access. This is useful when initializing a series of objects which involve existing database queries, where the uncompleted object should not yet be flushed.

classmethod sqlalchemy.orm.session.Session.object_session(instance)¶

inherited from the sqlalchemy.orm.session._SessionClassMethods.object_session method of sqlalchemy.orm.session._SessionClassMethods

Return the Session to which an object belongs.

This is an alias of object_session().

method sqlalchemy.orm.session.Session.prepare()¶

Prepare the current transaction in progress for two phase commit.

If no transaction is in progress, this method raises an InvalidRequestError.

Only root transactions of two phase sessions can be prepared. If the current transaction is not such, an InvalidRequestError is raised.

method sqlalchemy.orm.session.Session.prune()¶

Remove unreferenced instances cached in the identity map.

Deprecated since version 0.7: The Session.prune() method is deprecated along with Session.weak_identity_map. This method will be removed in a future release.

Note that this method is only meaningful if “weak_identity_map” is set to False. The default weak identity map is self-pruning.

Removes any object in this Session’s identity map that is not referenced in user code, modified, new or scheduled for deletion. Returns the number of objects pruned.

method sqlalchemy.orm.session.Session.query(*entities, **kwargs)¶: Return a new Query object corresponding to this Session.

method sqlalchemy.orm.session.Session.refresh(instance, attribute_names=None, with_for_update=None, lockmode=None)¶

Expire and refresh the attributes on the given instance.

A query will be issued to the database and all attributes will be refreshed with their current database value.

Lazy-loaded relational attributes will remain lazily loaded, so that the instance-wide refresh operation will be followed immediately by the lazy load of that attribute.

Eagerly-loaded relational attributes will eagerly load within the single refresh operation.

Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction - usage of Session.refresh() usually only makes sense if non-ORM SQL statement were emitted in the ongoing transaction, or if autocommit mode is turned on.

Parameters:

attribute_names – optional. An iterable collection of string attribute names indicating a subset of attributes to be refreshed.
with_for_update –
optional boolean True indicating FOR UPDATE should be used, or may be a dictionary containing flags to indicate a more specific set of FOR UPDATE flags for the SELECT; flags should match the parameters of Query.with_for_update(). Supersedes the Session.refresh.lockmode parameter.

New in version 1.2.
lockmode – Passed to the Query as used by Query.with_lockmode(). Superseded by Session.refresh.with_for_update.

See also

Refreshing / Expiring - introductory material

Session.expire()

Session.expire_all()

method sqlalchemy.orm.session.Session.rollback()¶

Rollback the current transaction in progress.

If no transaction is in progress, this method is a pass-through.

This method rolls back the current transaction or nested transaction regardless of subtransactions being in effect. All subtransactions up to the first real transaction are closed. Subtransactions occur when begin() is called multiple times.

See also

Rolling Back

method sqlalchemy.orm.session.Session.scalar(clause, params=None, mapper=None, bind=None, **kw)¶: Like Session.execute() but return a scalar result.

attribute sqlalchemy.orm.session.Session.transaction = None¶: The current active or inactive SessionTransaction.

class sqlalchemy.orm.session.SessionTransaction(session, parent=None, nested=False)¶

A Session-level transaction.

SessionTransaction is a mostly behind-the-scenes object not normally referenced directly by application code. It coordinates among multiple Connection objects, maintaining a database transaction for each one individually, committing or rolling them back all at once. It also provides optional two-phase commit behavior which can augment this coordination operation.

The Session.transaction attribute of Session refers to the current SessionTransaction object in use, if any. The SessionTransaction.parent attribute refers to the parent SessionTransaction in the stack of SessionTransaction objects. If this attribute is None, then this is the top of the stack. If non-None, then this SessionTransaction refers either to a so-called “subtransaction” or a “nested” transaction. A “subtransaction” is a scoping concept that demarcates an inner portion of the outermost “real” transaction. A nested transaction, which is indicated when the SessionTransaction.nested attribute is also True, indicates that this SessionTransaction corresponds to a SAVEPOINT.

Life Cycle

A SessionTransaction is associated with a Session in its default mode of autocommit=False immediately, associated with no database connections. As the Session is called upon to emit SQL on behalf of various Engine or Connection objects, a corresponding Connection and associated Transaction is added to a collection within the SessionTransaction object, becoming one of the connection/transaction pairs maintained by the SessionTransaction. The start of a SessionTransaction can be tracked using the SessionEvents.after_transaction_create() event.

The lifespan of the SessionTransaction ends when the Session.commit(), Session.rollback() or Session.close() methods are called. At this point, the SessionTransaction removes its association with its parent Session. A Session that is in autocommit=False mode will create a new SessionTransaction to replace it immediately, whereas a Session that’s in autocommit=True mode will remain without a SessionTransaction until the Session.begin() method is called. The end of a SessionTransaction can be tracked using the SessionEvents.after_transaction_end() event.

Nesting and Subtransactions

Another detail of SessionTransaction behavior is that it is capable of “nesting”. This means that the Session.begin() method can be called while an existing SessionTransaction is already present, producing a new SessionTransaction that temporarily replaces the parent SessionTransaction. When a SessionTransaction is produced as nested, it assigns itself to the Session.transaction attribute, and it additionally will assign the previous SessionTransaction to its Session.parent attribute. The behavior is effectively a stack, where Session.transaction refers to the current head of the stack, and the SessionTransaction.parent attribute allows traversal up the stack until SessionTransaction.parent is None, indicating the top of the stack.

When the scope of SessionTransaction is ended via Session.commit() or Session.rollback(), it restores its parent SessionTransaction back onto the Session.transaction attribute.

The purpose of this stack is to allow nesting of Session.rollback() or Session.commit() calls in context with various flavors of Session.begin(). This nesting behavior applies to when Session.begin_nested() is used to emit a SAVEPOINT transaction, and is also used to produce a so-called “subtransaction” which allows a block of code to use a begin/rollback/commit sequence regardless of whether or not its enclosing code block has begun a transaction. The flush() method, whether called explicitly or via autoflush, is the primary consumer of the “subtransaction” feature, in that it wishes to guarantee that it works within in a transaction block regardless of whether or not the Session is in transactional mode when the method is called.

Note that the flush process that occurs within the “autoflush” feature as well as when the Session.flush() method is used always creates a SessionTransaction object. This object is normally a subtransaction, unless the Session is in autocommit mode and no transaction exists at all, in which case it’s the outermost transaction. Any event-handling logic or other inspection logic needs to take into account whether a SessionTransaction is the outermost transaction, a subtransaction, or a “nested” / SAVEPOINT transaction.

Members

See also

Session.begin_nested()

Session.is_active

SessionEvents.after_transaction_create()

SessionEvents.after_transaction_end()

SessionEvents.after_commit()

SessionEvents.after_rollback()

SessionEvents.after_soft_rollback()

attribute sqlalchemy.orm.session.SessionTransaction.nested = False¶

Indicates if this is a nested, or SAVEPOINT, transaction.

When SessionTransaction.nested is True, it is expected that SessionTransaction.parent will be True as well.

attribute sqlalchemy.orm.session.SessionTransaction.parent¶

The parent SessionTransaction of this SessionTransaction.

If this attribute is None, indicates this SessionTransaction is at the top of the stack, and corresponds to a real “COMMIT”/”ROLLBACK” block. If non-None, then this is either a “subtransaction” or a “nested” / SAVEPOINT transaction. If the SessionTransaction.nested attribute is True, then this is a SAVEPOINT, and if False, indicates this a subtransaction.

New in version 1.0.16: - use ._parent for previous versions

Session Utilities¶

Object Name	Description
make_transient(instance)	Alter the state of the given instance so that it is transient.
make_transient_to_detached(instance)	Make the given transient instance detached.
object_session(instance)	Return the `Session` to which the given instance belongs.
was_deleted(object_)	Return True if the given object was deleted within a session flush.

function sqlalchemy.orm.session.make_transient(instance)¶

Alter the state of the given instance so that it is transient.

Note

make_transient() is a special-case function for advanced use cases only.

The given mapped instance is assumed to be in the persistent or detached state. The function will remove its association with any Session as well as its InstanceState.identity. The effect is that the object will behave as though it were newly constructed, except retaining any attribute / collection values that were loaded at the time of the call. The InstanceState.deleted flag is also reset if this object had been deleted as a result of using Session.delete().

Warning

make_transient() does not “unexpire” or otherwise eagerly load ORM-mapped attributes that are not currently loaded at the time the function is called. This includes attributes which:

were expired via Session.expire()
were expired as the natural effect of committing a session transaction, e.g. Session.commit()
are normally lazy loaded but are not currently loaded
are “deferred” via Deferred Column Loading and are not yet loaded
were not present in the query which loaded this object, such as that which is common in joined table inheritance and other scenarios.

After make_transient() is called, unloaded attributes such as those above will normally resolve to the value None when accessed, or an empty collection for a collection-oriented attribute. As the object is transient and un-associated with any database identity, it will no longer retrieve these values.

See also

make_transient_to_detached()

function sqlalchemy.orm.session.make_transient_to_detached(instance)¶

Make the given transient instance detached.

Note

make_transient_to_detached() is a special-case function for advanced use cases only.

All attribute history on the given instance will be reset as though the instance were freshly loaded from a query. Missing attributes will be marked as expired. The primary key attributes of the object, which are required, will be made into the “key” of the instance.

The object can then be added to a session, or merged possibly with the load=False flag, at which point it will look as if it were loaded that way, without emitting SQL.

This is a special use case function that differs from a normal call to Session.merge() in that a given persistent state can be manufactured without any SQL calls.

New in version 0.9.5.

See also

make_transient()

Session.enable_relationship_loading()

function sqlalchemy.orm.session.object_session(instance)¶

Return the Session to which the given instance belongs.

This is essentially the same as the InstanceState.session accessor. See that attribute for details.

function sqlalchemy.orm.util.was_deleted(object_)¶

Return True if the given object was deleted within a session flush.

This is regardless of whether or not the object is persistent or detached.

See also

InstanceState.was_deleted

Attribute and State Management Utilities¶

These functions are provided by the SQLAlchemy attribute instrumentation API to provide a detailed interface for dealing with instances, attribute values, and history. Some of them are useful when constructing event listener functions, such as those described in ORM Events.

Object Name	Description
del_attribute(instance, key)	Delete the value of an attribute, firing history events.
flag_dirty(instance)	Mark an instance as ‘dirty’ without any specific attribute mentioned.
flag_modified(instance, key)	Mark an attribute on an instance as ‘modified’.
get_attribute(instance, key)	Get the value of an attribute, firing any callables required.
get_history(obj, key[, passive])	Return a `History` record for the given object and attribute key.
History	A 3-tuple of added, unchanged and deleted values, representing the changes which have occurred on an instrumented attribute.
init_collection(obj, key)	Initialize a collection attribute and return the collection adapter.
instance_state	Return the `InstanceState` for a given mapped object.
is_instrumented(instance, key)	Return True if the given attribute on the given instance is instrumented by the attributes package.
object_state(instance)	Given an object, return the `InstanceState` associated with the object.
set_attribute(instance, key, value[, initiator])	Set the value of an attribute, firing history events.
set_committed_value(instance, key, value)	Set the value of an attribute with no history events.

function sqlalchemy.orm.util.object_state(instance)¶

Given an object, return the InstanceState associated with the object.

Raises sqlalchemy.orm.exc.UnmappedInstanceError if no mapping is configured.

Equivalent functionality is available via the inspect() function as:

inspect(instance)

Using the inspection system will raise sqlalchemy.exc.NoInspectionAvailable if the instance is not part of a mapping.

function sqlalchemy.orm.attributes.del_attribute(instance, key)¶

Delete the value of an attribute, firing history events.

This function may be used regardless of instrumentation applied directly to the class, i.e. no descriptors are required. Custom attribute management schemes will need to make usage of this method to establish attribute state as understood by SQLAlchemy.

function sqlalchemy.orm.attributes.get_attribute(instance, key)¶

Get the value of an attribute, firing any callables required.

This function may be used regardless of instrumentation applied directly to the class, i.e. no descriptors are required. Custom attribute management schemes will need to make usage of this method to make usage of attribute state as understood by SQLAlchemy.

function sqlalchemy.orm.attributes.get_history(obj, key, passive=symbol('PASSIVE_OFF'))¶

Return a History record for the given object and attribute key.

This is the pre-flush history for a given attribute, which is reset each time the Session flushes changes to the current database transaction.

Note

Prefer to use the AttributeState.history and AttributeState.load_history() accessors to retrieve the History for instance attributes.

Parameters:

obj – an object whose class is instrumented by the attributes package.
key – string attribute name.
passive – indicates loading behavior for the attribute if the value is not already present. This is a bitflag attribute, which defaults to the symbol PASSIVE_OFF indicating all necessary SQL should be emitted.

See also

AttributeState.history

AttributeState.load_history() - retrieve history using loader callables if the value is not locally present.

function sqlalchemy.orm.attributes.init_collection(obj, key)¶

Initialize a collection attribute and return the collection adapter.

This function is used to provide direct access to collection internals for a previously unloaded attribute. e.g.:

collection_adapter = init_collection(someobject, 'elements')
for elem in values:
    collection_adapter.append_without_event(elem)

For an easier way to do the above, see set_committed_value().

obj is an instrumented object instance. An InstanceState is accepted directly for backwards compatibility but this usage is deprecated.

function sqlalchemy.orm.attributes.flag_modified(instance, key)¶

Mark an attribute on an instance as ‘modified’.

This sets the ‘modified’ flag on the instance and establishes an unconditional change event for the given attribute. The attribute must have a value present, else an InvalidRequestError is raised.

To mark an object “dirty” without referring to any specific attribute so that it is considered within a flush, use the flag_dirty() call.

See also

flag_dirty()

function sqlalchemy.orm.attributes.flag_dirty(instance)¶

Mark an instance as ‘dirty’ without any specific attribute mentioned.

This is a special operation that will allow the object to travel through the flush process for interception by events such as SessionEvents.before_flush(). Note that no SQL will be emitted in the flush process for an object that has no changes, even if marked dirty via this method. However, a SessionEvents.before_flush() handler will be able to see the object in the Session.dirty collection and may establish changes on it, which will then be included in the SQL emitted.

New in version 1.2.

See also

flag_modified()

function sqlalchemy.orm.attributes.instance_state()¶

Return the InstanceState for a given mapped object.

This function is the internal version of object_state(). The object_state() and/or the inspect() function is preferred here as they each emit an informative exception if the given object is not mapped.

function sqlalchemy.orm.instrumentation.is_instrumented(instance, key)¶

Return True if the given attribute on the given instance is instrumented by the attributes package.

This function may be used regardless of instrumentation applied directly to the class, i.e. no descriptors are required.

function sqlalchemy.orm.attributes.set_attribute(instance, key, value, initiator=None)¶

Set the value of an attribute, firing history events.

This function may be used regardless of instrumentation applied directly to the class, i.e. no descriptors are required. Custom attribute management schemes will need to make usage of this method to establish attribute state as understood by SQLAlchemy.

Parameters:

instance – the object that will be modified
key – string name of the attribute
value – value to assign
initiator –
an instance of Event that would have been propagated from a previous event listener. This argument is used when the set_attribute() function is being used within an existing event listening function where an Event object is being supplied; the object may be used to track the origin of the chain of events.

New in version 1.2.3.

function sqlalchemy.orm.attributes.set_committed_value(instance, key, value)¶

Set the value of an attribute with no history events.

Cancels any previous history present. The value should be a scalar value for scalar-holding attributes, or an iterable for any collection-holding attribute.

This is the same underlying method used when a lazy loader fires off and loads additional data from the database. In particular, this method can be used by application code which has loaded additional attributes or collections through separate queries, which can then be attached to an instance as though it were part of its original loaded state.

class sqlalchemy.orm.attributes.History(added, unchanged, deleted)¶

A 3-tuple of added, unchanged and deleted values, representing the changes which have occurred on an instrumented attribute.

The easiest way to get a History object for a particular attribute on an object is to use the inspect() function:

from sqlalchemy import inspect

hist = inspect(myobject).attrs.myattribute.history

Each tuple member is an iterable sequence:

added - the collection of items added to the attribute (the first tuple element).
unchanged - the collection of items that have not changed on the attribute (the second tuple element).
deleted - the collection of items that have been removed from the attribute (the third tuple element).

Members

empty(), has_changes(), non_added(), non_deleted(), sum()

Class signature

class sqlalchemy.orm.attributes.History (sqlalchemy.orm.attributes.History)

method sqlalchemy.orm.attributes.History.empty()¶: Return True if this History has no changes and no existing, unchanged state.

method sqlalchemy.orm.attributes.History.has_changes()¶: Return True if this History has changes.

method sqlalchemy.orm.attributes.History.non_added()¶: Return a collection of unchanged + deleted.

method sqlalchemy.orm.attributes.History.non_deleted()¶: Return a collection of added + unchanged.

method sqlalchemy.orm.attributes.History.sum()¶: Return a collection of added + unchanged + deleted.

SQLAlchemy 1.2 Documentation

SQLAlchemy 1.2 Documentation

SQLAlchemy ORM

Session API¶

Session and sessionmaker()¶

Session Utilities¶

Attribute and State Management Utilities¶