SQLAlchemy 1.3 Documentation

method sqlalchemy.orm.events.MapperEvents.after_insert(mapper, connection, target)¶

Receive an object instance after an INSERT statement is emitted corresponding to that instance.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'after_insert')
def receive_after_insert(mapper, connection, target):
    "listen for the 'after_insert' event"

    # ... (event handling logic) ...

This event is used to modify in-Python-only state on the instance after an INSERT occurs, as well as to emit additional SQL statements on the given connection.

The event is often called for a batch of objects of the same class after their INSERT statements have been emitted at once in a previous step. In the extremely rare case that this is not desirable, the mapper() can be configured with batch=False, which will cause batches of instances to be broken up into individual (and more poorly performing) event->persist->event steps.

Warning

Mapper-level flush events only allow very limited operations, on attributes local to the row being operated upon only, as well as allowing any SQL to be emitted on the given Connection. Please read fully the notes at Mapper-level Events for guidelines on using these methods; generally, the SessionEvents.before_flush() method should be preferred for general on-flush changes.

Parameters:

mapper – the Mapper which is the target of this event.
connection – the Connection being used to emit INSERT statements for this instance. This provides a handle into the current transaction on the target database specific to this instance.
target – the mapped instance being persisted. If the event is configured with raw=True, this will instead be the InstanceState state-management object associated with the instance.

Returns:

No return value is supported by this event.

See also

method sqlalchemy.orm.events.MapperEvents.after_update(mapper, connection, target)¶

Receive an object instance after an UPDATE statement is emitted corresponding to that instance.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'after_update')
def receive_after_update(mapper, connection, target):
    "listen for the 'after_update' event"

    # ... (event handling logic) ...

This event is used to modify in-Python-only state on the instance after an UPDATE occurs, as well as to emit additional SQL statements on the given connection.

This method is called for all instances that are marked as “dirty”, even those which have no net changes to their column-based attributes, and for which no UPDATE statement has proceeded. An object is marked as dirty when any of its column-based attributes have a “set attribute” operation called or when any of its collections are modified. If, at update time, no column-based attributes have any net changes, no UPDATE statement will be issued. This means that an instance being sent to MapperEvents.after_update() is not a guarantee that an UPDATE statement has been issued.

To detect if the column-based attributes on the object have net changes, and therefore resulted in an UPDATE statement, use object_session(instance).is_modified(instance, include_collections=False).

The event is often called for a batch of objects of the same class after their UPDATE statements have been emitted at once in a previous step. In the extremely rare case that this is not desirable, the mapper() can be configured with batch=False, which will cause batches of instances to be broken up into individual (and more poorly performing) event->persist->event steps.

Warning

Mapper-level flush events only allow very limited operations, on attributes local to the row being operated upon only, as well as allowing any SQL to be emitted on the given Connection. Please read fully the notes at Mapper-level Events for guidelines on using these methods; generally, the SessionEvents.before_flush() method should be preferred for general on-flush changes.

Parameters:

mapper – the Mapper which is the target of this event.
connection – the Connection being used to emit UPDATE statements for this instance. This provides a handle into the current transaction on the target database specific to this instance.
target – the mapped instance being persisted. If the event is configured with raw=True, this will instead be the InstanceState state-management object associated with the instance.

Returns:

No return value is supported by this event.

See also

MapperEvents.mapper_configured()

method sqlalchemy.orm.events.MapperEvents.before_configured()¶

Called before a series of mappers have been configured.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'before_configured')
def receive_before_configured():
    "listen for the 'before_configured' event"

    # ... (event handling logic) ...

The MapperEvents.before_configured() event is invoked each time the configure_mappers() function is invoked, before the function has done any of its work. configure_mappers() is typically invoked automatically as mappings are first used, as well as each time new mappers have been made available and new mapper use is detected.

This event can only be applied to the Mapper class or mapper() function, and not to individual mappings or mapped classes. It is only invoked for all mappings as a whole:

from sqlalchemy.orm import mapper

@event.listens_for(mapper, "before_configured")
def go():
    # ...

Contrast this event to MapperEvents.after_configured(), which is invoked after the series of mappers has been configured, as well as MapperEvents.before_mapper_configured() and MapperEvents.mapper_configured(), which are both invoked on a per-mapper basis.

Theoretically this event is called once per application, but is actually called any time new mappers are to be affected by a configure_mappers() call. If new mappings are constructed after existing ones have already been used, this event will likely be called again. To ensure that a particular event is only called once and no further, the once=True argument (new in 0.9.4) can be applied:

from sqlalchemy.orm import mapper

@event.listens_for(mapper, "before_configured", once=True)
def go():
    # ...

New in version 0.9.3.

MapperEvents.after_configured()

method sqlalchemy.orm.events.MapperEvents.before_delete(mapper, connection, target)¶

Receive an object instance before a DELETE statement is emitted corresponding to that instance.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'before_delete')
def receive_before_delete(mapper, connection, target):
    "listen for the 'before_delete' event"

    # ... (event handling logic) ...

This event is used to emit additional SQL statements on the given connection as well as to perform application specific bookkeeping related to a deletion event.

The event is often called for a batch of objects of the same class before their DELETE statements are emitted at once in a later step.

Warning

Mapper-level flush events only allow very limited operations, on attributes local to the row being operated upon only, as well as allowing any SQL to be emitted on the given Connection. Please read fully the notes at Mapper-level Events for guidelines on using these methods; generally, the SessionEvents.before_flush() method should be preferred for general on-flush changes.

Parameters:

mapper – the Mapper which is the target of this event.
connection – the Connection being used to emit DELETE statements for this instance. This provides a handle into the current transaction on the target database specific to this instance.
target – the mapped instance being deleted. If the event is configured with raw=True, this will instead be the InstanceState state-management object associated with the instance.

Returns:

No return value is supported by this event.

See also

method sqlalchemy.orm.events.MapperEvents.before_insert(mapper, connection, target)¶

Receive an object instance before an INSERT statement is emitted corresponding to that instance.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'before_insert')
def receive_before_insert(mapper, connection, target):
    "listen for the 'before_insert' event"

    # ... (event handling logic) ...

This event is used to modify local, non-object related attributes on the instance before an INSERT occurs, as well as to emit additional SQL statements on the given connection.

The event is often called for a batch of objects of the same class before their INSERT statements are emitted at once in a later step. In the extremely rare case that this is not desirable, the mapper() can be configured with batch=False, which will cause batches of instances to be broken up into individual (and more poorly performing) event->persist->event steps.

Warning

Mapper-level flush events only allow very limited operations, on attributes local to the row being operated upon only, as well as allowing any SQL to be emitted on the given Connection. Please read fully the notes at Mapper-level Events for guidelines on using these methods; generally, the SessionEvents.before_flush() method should be preferred for general on-flush changes.

Parameters:

mapper – the Mapper which is the target of this event.
connection – the Connection being used to emit INSERT statements for this instance. This provides a handle into the current transaction on the target database specific to this instance.
target – the mapped instance being persisted. If the event is configured with raw=True, this will instead be the InstanceState state-management object associated with the instance.

Returns:

No return value is supported by this event.

See also

MapperEvents.before_configured()

method sqlalchemy.orm.events.MapperEvents.before_mapper_configured(mapper, class_)¶

Called right before a specific mapper is to be configured.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'before_mapper_configured')
def receive_before_mapper_configured(mapper, class_):
    "listen for the 'before_mapper_configured' event"

    # ... (event handling logic) ...

This event is intended to allow a specific mapper to be skipped during the configure step, by returning the interfaces.EXT_SKIP symbol which indicates to the configure_mappers() call that this particular mapper (or hierarchy of mappers, if propagate=True is used) should be skipped in the current configuration run. When one or more mappers are skipped, the he “new mappers” flag will remain set, meaning the configure_mappers() function will continue to be called when mappers are used, to continue to try to configure all available mappers.

In comparison to the other configure-level events, MapperEvents.before_configured(), MapperEvents.after_configured(), and MapperEvents.mapper_configured(), the :meth;`.MapperEvents.before_mapper_configured` event provides for a meaningful return value when it is registered with the retval=True parameter.

New in version 1.3.

e.g.:

from sqlalchemy.orm import EXT_SKIP

Base = declarative_base()

DontConfigureBase = declarative_base()

@event.listens_for(
    DontConfigureBase,
    "before_mapper_configured", retval=True, propagate=True)
def dont_configure(mapper, cls):
    return EXT_SKIP

See also

MapperEvents.after_configured()

MapperEvents.mapper_configured()

method sqlalchemy.orm.events.MapperEvents.before_update(mapper, connection, target)¶

Receive an object instance before an UPDATE statement is emitted corresponding to that instance.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'before_update')
def receive_before_update(mapper, connection, target):
    "listen for the 'before_update' event"

    # ... (event handling logic) ...

This event is used to modify local, non-object related attributes on the instance before an UPDATE occurs, as well as to emit additional SQL statements on the given connection.

This method is called for all instances that are marked as “dirty”, even those which have no net changes to their column-based attributes. An object is marked as dirty when any of its column-based attributes have a “set attribute” operation called or when any of its collections are modified. If, at update time, no column-based attributes have any net changes, no UPDATE statement will be issued. This means that an instance being sent to MapperEvents.before_update() is not a guarantee that an UPDATE statement will be issued, although you can affect the outcome here by modifying attributes so that a net change in value does exist.

To detect if the column-based attributes on the object have net changes, and will therefore generate an UPDATE statement, use object_session(instance).is_modified(instance, include_collections=False).

The event is often called for a batch of objects of the same class before their UPDATE statements are emitted at once in a later step. In the extremely rare case that this is not desirable, the mapper() can be configured with batch=False, which will cause batches of instances to be broken up into individual (and more poorly performing) event->persist->event steps.

Warning

Mapper-level flush events only allow very limited operations, on attributes local to the row being operated upon only, as well as allowing any SQL to be emitted on the given Connection. Please read fully the notes at Mapper-level Events for guidelines on using these methods; generally, the SessionEvents.before_flush() method should be preferred for general on-flush changes.

Parameters:

mapper – the Mapper which is the target of this event.
connection – the Connection being used to emit UPDATE statements for this instance. This provides a handle into the current transaction on the target database specific to this instance.
target – the mapped instance being persisted. If the event is configured with raw=True, this will instead be the InstanceState state-management object associated with the instance.

Returns:

No return value is supported by this event.

See also

MapperEvents.before_configured()

method sqlalchemy.orm.events.MapperEvents.instrument_class(mapper, class_)¶

Receive a class when the mapper is first constructed, before instrumentation is applied to the mapped class.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'instrument_class')
def receive_instrument_class(mapper, class_):
    "listen for the 'instrument_class' event"

    # ... (event handling logic) ...

This event is the earliest phase of mapper construction. Most attributes of the mapper are not yet initialized.

This listener can either be applied to the Mapper class overall, or to any un-mapped class which serves as a base for classes that will be mapped (using the propagate=True flag):

Base = declarative_base()

@event.listens_for(Base, "instrument_class", propagate=True)
def on_new_class(mapper, cls_):
    " ... "

Parameters:

mapper – the Mapper which is the target of this event.
class_ – the mapped class.

method sqlalchemy.orm.events.MapperEvents.mapper_configured(mapper, class_)¶

Called when a specific mapper has completed its own configuration within the scope of the configure_mappers() call.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'mapper_configured')
def receive_mapper_configured(mapper, class_):
    "listen for the 'mapper_configured' event"

    # ... (event handling logic) ...

The MapperEvents.mapper_configured() event is invoked for each mapper that is encountered when the configure_mappers() function proceeds through the current list of not-yet-configured mappers. configure_mappers() is typically invoked automatically as mappings are first used, as well as each time new mappers have been made available and new mapper use is detected.

When the event is called, the mapper should be in its final state, but not including backrefs that may be invoked from other mappers; they might still be pending within the configuration operation. Bidirectional relationships that are instead configured via the relationship.back_populates argument will be fully available, since this style of relationship does not rely upon other possibly-not-configured mappers to know that they exist.

For an event that is guaranteed to have all mappers ready to go including backrefs that are defined only on other mappings, use the MapperEvents.after_configured() event; this event invokes only after all known mappings have been fully configured.

The MapperEvents.mapper_configured() event, unlike MapperEvents.before_configured() or MapperEvents.after_configured(), is called for each mapper/class individually, and the mapper is passed to the event itself. It also is called exactly once for a particular mapper. The event is therefore useful for configurational steps that benefit from being invoked just once on a specific mapper basis, which don’t require that “backref” configurations are necessarily ready yet.

Parameters:

mapper – the Mapper which is the target of this event.
class_ – the mapped class.

See also

MapperEvents.after_configured()

MapperEvents.before_mapper_configured()

Instance Events¶

Object Name	Description
InstanceEvents	Define events specific to object lifecycle.

class sqlalchemy.orm.events.InstanceEvents¶

Define events specific to object lifecycle.

e.g.:

from sqlalchemy import event

def my_load_listener(target, context):
    print("on load!")

event.listen(SomeClass, 'load', my_load_listener)

Available targets include:

mapped classes
unmapped superclasses of mapped or to-be-mapped classes (using the propagate=True flag)
Mapper objects
the Mapper class itself and the mapper() function indicate listening for all mappers.

Instance events are closely related to mapper events, but are more specific to the instance and its instrumentation, rather than its system of persistence.

When using InstanceEvents, several modifiers are available to the listen() function.

Parameters:

propagate=False – When True, the event listener should be applied to all inheriting classes as well as the class which is the target of this listener.
raw=False – When True, the “target” argument passed to applicable event listener functions will be the instance’s InstanceState management object, rather than the mapped instance itself.
restore_load_context=False –
Applies to the InstanceEvents.load() and InstanceEvents.refresh() events. Restores the loader context of the object when the event hook is complete, so that ongoing eager load operations continue to target the object appropriately. A warning is emitted if the object is moved to a new loader context from within one of these events if this flag is not set.

New in version 1.3.14.

Members

expire(), first_init(), init(), init_failure(), load(), pickle(), refresh(), refresh_flush(), unpickle()

Class signature

class sqlalchemy.orm.events.InstanceEvents (sqlalchemy.event.Events)

method sqlalchemy.orm.events.InstanceEvents.expire(target, attrs)¶

Receive an object instance after its attributes or some subset have been expired.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'expire')
def receive_expire(target, attrs):
    "listen for the 'expire' event"

    # ... (event handling logic) ...

‘keys’ is a list of attribute names. If None, the entire state was expired.

Parameters:

target – the mapped instance. If the event is configured with raw=True, this will instead be the InstanceState state-management object associated with the instance.
attrs – sequence of attribute names which were expired, or None if all attributes were expired.

method sqlalchemy.orm.events.InstanceEvents.first_init(manager, cls)¶

Called when the first instance of a particular mapping is called.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'first_init')
def receive_first_init(manager, cls):
    "listen for the 'first_init' event"

    # ... (event handling logic) ...

This event is called when the __init__ method of a class is called the first time for that particular class. The event invokes before __init__ actually proceeds as well as before the InstanceEvents.init() event is invoked.

method sqlalchemy.orm.events.InstanceEvents.init(target, args, kwargs)¶

Receive an instance when its constructor is called.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'init')
def receive_init(target, args, kwargs):
    "listen for the 'init' event"

    # ... (event handling logic) ...

This method is only called during a userland construction of an object, in conjunction with the object’s constructor, e.g. its __init__ method. It is not called when an object is loaded from the database; see the InstanceEvents.load() event in order to intercept a database load.

The event is called before the actual __init__ constructor of the object is called. The kwargs dictionary may be modified in-place in order to affect what is passed to __init__.

Parameters:

target – the mapped instance. If the event is configured with raw=True, this will instead be the InstanceState state-management object associated with the instance.
args – positional arguments passed to the __init__ method. This is passed as a tuple and is currently immutable.
kwargs – keyword arguments passed to the __init__ method. This structure can be altered in place.

See also

InstanceEvents.init_failure()

InstanceEvents.load()

method sqlalchemy.orm.events.InstanceEvents.init_failure(target, args, kwargs)¶

Receive an instance when its constructor has been called, and raised an exception.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'init_failure')
def receive_init_failure(target, args, kwargs):
    "listen for the 'init_failure' event"

    # ... (event handling logic) ...

This method is only called during a userland construction of an object, in conjunction with the object’s constructor, e.g. its __init__ method. It is not called when an object is loaded from the database.

The event is invoked after an exception raised by the __init__ method is caught. After the event is invoked, the original exception is re-raised outwards, so that the construction of the object still raises an exception. The actual exception and stack trace raised should be present in sys.exc_info().

Parameters:

target – the mapped instance. If the event is configured with raw=True, this will instead be the InstanceState state-management object associated with the instance.
args – positional arguments that were passed to the __init__ method.
kwargs – keyword arguments that were passed to the __init__ method.

See also

InstanceEvents.init()

InstanceEvents.load()

method sqlalchemy.orm.events.InstanceEvents.load(target, context)¶

Receive an object instance after it has been created via __new__, and after initial attribute population has occurred.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'load')
def receive_load(target, context):
    "listen for the 'load' event"

    # ... (event handling logic) ...

This typically occurs when the instance is created based on incoming result rows, and is only called once for that instance’s lifetime.

Warning

During a result-row load, this event is invoked when the first row received for this instance is processed. When using eager loading with collection-oriented attributes, the additional rows that are to be loaded / processed in order to load subsequent collection items have not occurred yet. This has the effect both that collections will not be fully loaded, as well as that if an operation occurs within this event handler that emits another database load operation for the object, the “loading context” for the object can change and interfere with the existing eager loaders still in progress.

Examples of what can cause the “loading context” to change within the event handler include, but are not necessarily limited to:

accessing deferred attributes that weren’t part of the row, will trigger an “undefer” operation and refresh the object
accessing attributes on a joined-inheritance subclass that weren’t part of the row, will trigger a refresh operation.

As of SQLAlchemy 1.3.14, a warning is emitted when this occurs. The InstanceEvents.restore_load_context option may be used on the event to prevent this warning; this will ensure that the existing loading context is maintained for the object after the event is called:

@event.listens_for(
    SomeClass, "load", restore_load_context=True)
def on_load(instance, context):
    instance.some_unloaded_attribute

Changed in version 1.3.14: Added InstanceEvents.restore_load_context and SessionEvents.restore_load_context flags which apply to “on load” events, which will ensure that the loading context for an object is restored when the event hook is complete; a warning is emitted if the load context of the object changes without this flag being set.

The InstanceEvents.load() event is also available in a class-method decorator format called reconstructor().

Parameters:

target – the mapped instance. If the event is configured with raw=True, this will instead be the InstanceState state-management object associated with the instance.
context – the QueryContext corresponding to the current Query in progress. This argument may be None if the load does not correspond to a Query, such as during Session.merge().

See also

InstanceEvents.init()

InstanceEvents.refresh()

SessionEvents.loaded_as_persistent()

Constructors and Object Initialization

method sqlalchemy.orm.events.InstanceEvents.pickle(target, state_dict)¶

Receive an object instance when its associated state is being pickled.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'pickle')
def receive_pickle(target, state_dict):
    "listen for the 'pickle' event"

    # ... (event handling logic) ...

Parameters:

target – the mapped instance. If the event is configured with raw=True, this will instead be the InstanceState state-management object associated with the instance.
state_dict – the dictionary returned by __getstate__, containing the state to be pickled.

method sqlalchemy.orm.events.InstanceEvents.refresh(target, context, attrs)¶

Receive an object instance after one or more attributes have been refreshed from a query.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'refresh')
def receive_refresh(target, context, attrs):
    "listen for the 'refresh' event"

    # ... (event handling logic) ...

Contrast this to the InstanceEvents.load() method, which is invoked when the object is first loaded from a query.

Note

This event is invoked within the loader process before eager loaders may have been completed, and the object’s state may not be complete. Additionally, invoking row-level refresh operations on the object will place the object into a new loader context, interfering with the existing load context. See the note on InstanceEvents.load() for background on making use of the InstanceEvents.restore_load_context parameter, in order to resolve this scenario.

Parameters:

target – the mapped instance. If the event is configured with raw=True, this will instead be the InstanceState state-management object associated with the instance.
context – the QueryContext corresponding to the current Query in progress.
attrs – sequence of attribute names which were populated, or None if all column-mapped, non-deferred attributes were populated.

See also

InstanceEvents.load()

method sqlalchemy.orm.events.InstanceEvents.refresh_flush(target, flush_context, attrs)¶

Receive an object instance after one or more attributes that contain a column-level default or onupdate handler have been refreshed during persistence of the object’s state.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'refresh_flush')
def receive_refresh_flush(target, flush_context, attrs):
    "listen for the 'refresh_flush' event"

    # ... (event handling logic) ...

This event is the same as InstanceEvents.refresh() except it is invoked within the unit of work flush process, and includes only non-primary-key columns that have column level default or onupdate handlers, including Python callables as well as server side defaults and triggers which may be fetched via the RETURNING clause.

Note

While the InstanceEvents.refresh_flush() event is triggered for an object that was INSERTed as well as for an object that was UPDATEd, the event is geared primarily towards the UPDATE process; it is mostly an internal artifact that INSERT actions can also trigger this event, and note that primary key columns for an INSERTed row are explicitly omitted from this event. In order to intercept the newly INSERTed state of an object, the SessionEvents.pending_to_persistent() and MapperEvents.after_insert() are better choices.

New in version 1.0.5.

Parameters:

target – the mapped instance. If the event is configured with raw=True, this will instead be the InstanceState state-management object associated with the instance.
flush_context – Internal UOWTransaction object which handles the details of the flush.
attrs – sequence of attribute names which were populated.

See also

Fetching Server-Generated Defaults

Column INSERT/UPDATE Defaults

method sqlalchemy.orm.events.InstanceEvents.unpickle(target, state_dict)¶

Receive an object instance after its associated state has been unpickled.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeClass, 'unpickle')
def receive_unpickle(target, state_dict):
    "listen for the 'unpickle' event"

    # ... (event handling logic) ...

Parameters:

target – the mapped instance. If the event is configured with raw=True, this will instead be the InstanceState state-management object associated with the instance.
state_dict – the dictionary sent to __setstate__, containing the state dictionary which was pickled.

Session Events¶

Object Name	Description
SessionEvents	Define events specific to `Session` lifecycle.

class sqlalchemy.orm.events.SessionEvents¶

Define events specific to Session lifecycle.

e.g.:

from sqlalchemy import event
from sqlalchemy.orm import sessionmaker

def my_before_commit(session):
    print("before commit!")

Session = sessionmaker()

event.listen(Session, "before_commit", my_before_commit)

The listen() function will accept Session objects as well as the return result of sessionmaker() and scoped_session().

Additionally, it accepts the Session class which will apply listeners to all Session instances globally.

Parameters:

raw=False –
When True, the “target” argument passed to applicable event listener functions that work on individual objects will be the instance’s InstanceState management object, rather than the mapped instance itself.

New in version 1.3.14.
restore_load_context=False –
Applies to the SessionEvents.loaded_as_persistent() event. Restores the loader context of the object when the event hook is complete, so that ongoing eager load operations continue to target the object appropriately. A warning is emitted if the object is moved to a new loader context from within this event if this flag is not set.

New in version 1.3.14.

Class signature

class sqlalchemy.orm.events.SessionEvents (sqlalchemy.event.Events)

method sqlalchemy.orm.events.SessionEvents.after_attach(session, instance)¶

Execute after an instance is attached to a session.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'after_attach')
def receive_after_attach(session, instance):
    "listen for the 'after_attach' event"

    # ... (event handling logic) ...

This is called after an add, delete or merge.

Note

As of 0.8, this event fires off after the item has been fully associated with the session, which is different than previous releases. For event handlers that require the object not yet be part of session state (such as handlers which may autoflush while the target object is not yet complete) consider the new before_attach() event.

See also

SessionEvents.before_attach()

SessionEvents.before_commit()

method sqlalchemy.orm.events.SessionEvents.after_begin(session, transaction, connection)¶

Execute after a transaction is begun on a connection

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'after_begin')
def receive_after_begin(session, transaction, connection):
    "listen for the 'after_begin' event"

    # ... (event handling logic) ...

Parameters:

session – The target Session.
transaction – The SessionTransaction.
connection – The Connection object which will be used for SQL statements.

See also

SessionEvents.after_commit()

QueryEvents.before_compile_delete()

method sqlalchemy.orm.events.SessionEvents.after_bulk_delete(delete_context)¶

Execute after a bulk delete operation to the session.

Example argument forms:

from sqlalchemy import event

# standard decorator style (arguments as of 0.9)
@event.listens_for(SomeSessionOrFactory, 'after_bulk_delete')
def receive_after_bulk_delete(delete_context):
    "listen for the 'after_bulk_delete' event"

    # ... (event handling logic) ...

# DEPRECATED calling style (pre-0.9, will be removed in a future release)
@event.listens_for(SomeSessionOrFactory, 'after_bulk_delete')
def receive_after_bulk_delete(session, query, query_context, result):
    "listen for the 'after_bulk_delete' event"

    # ... (event handling logic) ...

Deprecated since version 0.9: The after_bulk_delete event now accepts the arguments delete_context. Support for listener functions which accept the previous argument signature(s) listed above as “deprecated” will be removed in a future release.

This is called as a result of the Query.delete() method.

Parameters:

delete_context –

a “delete context” object which contains details about the update, including these attributes:

session - the Session involved

query -the Query object that this update operation was called upon.

context The QueryContext object, corresponding to the invocation of an ORM query.

result the ResultProxy returned as a result of the bulk DELETE operation.

See also

SessionEvents.after_bulk_update()

method sqlalchemy.orm.events.SessionEvents.after_bulk_update(update_context)¶

Execute after a bulk update operation to the session.

Example argument forms:

from sqlalchemy import event

# standard decorator style (arguments as of 0.9)
@event.listens_for(SomeSessionOrFactory, 'after_bulk_update')
def receive_after_bulk_update(update_context):
    "listen for the 'after_bulk_update' event"

    # ... (event handling logic) ...

# DEPRECATED calling style (pre-0.9, will be removed in a future release)
@event.listens_for(SomeSessionOrFactory, 'after_bulk_update')
def receive_after_bulk_update(session, query, query_context, result):
    "listen for the 'after_bulk_update' event"

    # ... (event handling logic) ...

Deprecated since version 0.9: The after_bulk_update event now accepts the arguments update_context. Support for listener functions which accept the previous argument signature(s) listed above as “deprecated” will be removed in a future release.

This is called as a result of the Query.update() method.

Parameters:

update_context –

an “update context” object which contains details about the update, including these attributes:

session - the Session involved

query -the Query object that this update operation was called upon.

values The “values” dictionary that was passed to Query.update().

context The QueryContext object, corresponding to the invocation of an ORM query.

result the ResultProxy returned as a result of the bulk UPDATE operation.

See also

QueryEvents.before_compile_update()

SessionEvents.after_bulk_delete()

method sqlalchemy.orm.events.SessionEvents.after_commit(session)¶

Execute after a commit has occurred.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'after_commit')
def receive_after_commit(session):
    "listen for the 'after_commit' event"

    # ... (event handling logic) ...

Note

The SessionEvents.after_commit() hook is not per-flush, that is, the Session can emit SQL to the database many times within the scope of a transaction. For interception of these events, use the SessionEvents.before_flush(), SessionEvents.after_flush(), or SessionEvents.after_flush_postexec() events.

Note

The Session is not in an active transaction when the SessionEvents.after_commit() event is invoked, and therefore can not emit SQL. To emit SQL corresponding to every transaction, use the SessionEvents.before_commit() event.

Parameters:: session – The target Session.

See also

SessionEvents.before_commit()

SessionEvents.after_begin()

SessionEvents.before_flush()

method sqlalchemy.orm.events.SessionEvents.after_flush(session, flush_context)¶

Execute after flush has completed, but before commit has been called.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'after_flush')
def receive_after_flush(session, flush_context):
    "listen for the 'after_flush' event"

    # ... (event handling logic) ...

Note that the session’s state is still in pre-flush, i.e. ‘new’, ‘dirty’, and ‘deleted’ lists still show pre-flush state as well as the history settings on instance attributes.

Warning

This event runs after the Session has emitted SQL to modify the database, but before it has altered its internal state to reflect those changes, including that newly inserted objects are placed into the identity map. ORM operations emitted within this event such as loads of related items may produce new identity map entries that will immediately be replaced, sometimes causing confusing results. SQLAlchemy will emit a warning for this condition as of version 1.3.9.

Parameters:

session – The target Session.
flush_context – Internal UOWTransaction object which handles the details of the flush.

See also

SessionEvents.after_flush_postexec()

SessionEvents.before_flush()

method sqlalchemy.orm.events.SessionEvents.after_flush_postexec(session, flush_context)¶

Execute after flush has completed, and after the post-exec state occurs.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'after_flush_postexec')
def receive_after_flush_postexec(session, flush_context):
    "listen for the 'after_flush_postexec' event"

    # ... (event handling logic) ...

This will be when the ‘new’, ‘dirty’, and ‘deleted’ lists are in their final state. An actual commit() may or may not have occurred, depending on whether or not the flush started its own transaction or participated in a larger transaction.

Parameters:

session – The target Session.
flush_context – Internal UOWTransaction object which handles the details of the flush.

See also

SessionEvents.after_flush()

method sqlalchemy.orm.events.SessionEvents.after_rollback(session)¶

Execute after a real DBAPI rollback has occurred.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'after_rollback')
def receive_after_rollback(session):
    "listen for the 'after_rollback' event"

    # ... (event handling logic) ...

Note that this event only fires when the actual rollback against the database occurs - it does not fire each time the Session.rollback() method is called, if the underlying DBAPI transaction has already been rolled back. In many cases, the Session will not be in an “active” state during this event, as the current transaction is not valid. To acquire a Session which is active after the outermost rollback has proceeded, use the SessionEvents.after_soft_rollback() event, checking the Session.is_active flag.

Parameters:: session – The target Session.

method sqlalchemy.orm.events.SessionEvents.after_soft_rollback(session, previous_transaction)¶

Execute after any rollback has occurred, including “soft” rollbacks that don’t actually emit at the DBAPI level.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'after_soft_rollback')
def receive_after_soft_rollback(session, previous_transaction):
    "listen for the 'after_soft_rollback' event"

    # ... (event handling logic) ...

This corresponds to both nested and outer rollbacks, i.e. the innermost rollback that calls the DBAPI’s rollback() method, as well as the enclosing rollback calls that only pop themselves from the transaction stack.

The given Session can be used to invoke SQL and Session.query() operations after an outermost rollback by first checking the Session.is_active flag:

@event.listens_for(Session, "after_soft_rollback")
def do_something(session, previous_transaction):
    if session.is_active:
        session.execute("select * from some_table")

Parameters:

session – The target Session.
previous_transaction – The SessionTransaction transactional marker object which was just closed. The current SessionTransaction for the given Session is available via the Session.transaction attribute.

method sqlalchemy.orm.events.SessionEvents.after_transaction_create(session, transaction)¶

Execute when a new SessionTransaction is created.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'after_transaction_create')
def receive_after_transaction_create(session, transaction):
    "listen for the 'after_transaction_create' event"

    # ... (event handling logic) ...

This event differs from SessionEvents.after_begin() in that it occurs for each SessionTransaction overall, as opposed to when transactions are begun on individual database connections. It is also invoked for nested transactions and subtransactions, and is always matched by a corresponding SessionEvents.after_transaction_end() event (assuming normal operation of the Session).

Parameters:

session – the target Session.

transaction –

the target SessionTransaction.

To detect if this is the outermost SessionTransaction, as opposed to a “subtransaction” or a SAVEPOINT, test that the SessionTransaction.parent attribute is None:

@event.listens_for(session, "after_transaction_create")
def after_transaction_create(session, transaction):
    if transaction.parent is None:
        # work with top-level transaction

To detect if the SessionTransaction is a SAVEPOINT, use the SessionTransaction.nested attribute:

@event.listens_for(session, "after_transaction_create")
def after_transaction_create(session, transaction):
    if transaction.nested:
        # work with SAVEPOINT transaction

See also

SessionTransaction

method sqlalchemy.orm.events.SessionEvents.after_transaction_end(session, transaction)¶

Execute when the span of a SessionTransaction ends.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'after_transaction_end')
def receive_after_transaction_end(session, transaction):
    "listen for the 'after_transaction_end' event"

    # ... (event handling logic) ...

This event differs from SessionEvents.after_commit() in that it corresponds to all SessionTransaction objects in use, including those for nested transactions and subtransactions, and is always matched by a corresponding SessionEvents.after_transaction_create() event.

Parameters:

session – the target Session.

transaction –

the target SessionTransaction.

To detect if this is the outermost SessionTransaction, as opposed to a “subtransaction” or a SAVEPOINT, test that the SessionTransaction.parent attribute is None:

@event.listens_for(session, "after_transaction_create")
def after_transaction_end(session, transaction):
    if transaction.parent is None:
        # work with top-level transaction

To detect if the SessionTransaction is a SAVEPOINT, use the SessionTransaction.nested attribute:

@event.listens_for(session, "after_transaction_create")
def after_transaction_end(session, transaction):
    if transaction.nested:
        # work with SAVEPOINT transaction

See also

SessionTransaction

SessionEvents.after_attach()

method sqlalchemy.orm.events.SessionEvents.before_attach(session, instance)¶

Execute before an instance is attached to a session.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'before_attach')
def receive_before_attach(session, instance):
    "listen for the 'before_attach' event"

    # ... (event handling logic) ...

This is called before an add, delete or merge causes the object to be part of the session.

See also

SessionEvents.after_commit()

method sqlalchemy.orm.events.SessionEvents.before_commit(session)¶

Execute before commit is called.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'before_commit')
def receive_before_commit(session):
    "listen for the 'before_commit' event"

    # ... (event handling logic) ...

Note

The SessionEvents.before_commit() hook is not per-flush, that is, the Session can emit SQL to the database many times within the scope of a transaction. For interception of these events, use the SessionEvents.before_flush(), SessionEvents.after_flush(), or SessionEvents.after_flush_postexec() events.

Parameters:: session – The target Session.

See also

SessionEvents.after_begin()

SessionEvents.after_flush()

method sqlalchemy.orm.events.SessionEvents.before_flush(session, flush_context, instances)¶

Execute before flush process has started.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'before_flush')
def receive_before_flush(session, flush_context, instances):
    "listen for the 'before_flush' event"

    # ... (event handling logic) ...

Parameters:

session – The target Session.
flush_context – Internal UOWTransaction object which handles the details of the flush.
instances – Usually None, this is the collection of objects which can be passed to the Session.flush() method (note this usage is deprecated).

See also

SessionEvents.after_flush_postexec()

method sqlalchemy.orm.events.SessionEvents.deleted_to_detached(session, instance)¶

Intercept the “deleted to detached” transition for a specific object.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'deleted_to_detached')
def receive_deleted_to_detached(session, instance):
    "listen for the 'deleted_to_detached' event"

    # ... (event handling logic) ...

This event is invoked when a deleted object is evicted from the session. The typical case when this occurs is when the transaction for a Session in which the object was deleted is committed; the object moves from the deleted state to the detached state.

It is also invoked for objects that were deleted in a flush when the Session.expunge_all() or Session.close() events are called, as well as if the object is individually expunged from its deleted state via Session.expunge().

New in version 1.1.

See also

method sqlalchemy.orm.events.SessionEvents.deleted_to_persistent(session, instance)¶

Intercept the “deleted to persistent” transition for a specific object.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'deleted_to_persistent')
def receive_deleted_to_persistent(session, instance):
    "listen for the 'deleted_to_persistent' event"

    # ... (event handling logic) ...

This transition occurs only when an object that’s been deleted successfully in a flush is restored due to a call to Session.rollback(). The event is not called under any other circumstances.

New in version 1.1.

See also

method sqlalchemy.orm.events.SessionEvents.detached_to_persistent(session, instance)¶

Intercept the “detached to persistent” transition for a specific object.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'detached_to_persistent')
def receive_detached_to_persistent(session, instance):
    "listen for the 'detached_to_persistent' event"

    # ... (event handling logic) ...

This event is a specialization of the SessionEvents.after_attach() event which is only invoked for this specific transition. It is invoked typically during the Session.add() call, as well as during the Session.delete() call if the object was not previously associated with the Session (note that an object marked as “deleted” remains in the “persistent” state until the flush proceeds).

Note

If the object becomes persistent as part of a call to Session.delete(), the object is not yet marked as deleted when this event is called. To detect deleted objects, check the deleted flag sent to the SessionEvents.persistent_to_detached() to event after the flush proceeds, or check the Session.deleted collection within the SessionEvents.before_flush() event if deleted objects need to be intercepted before the flush.

Parameters:

session – target Session
instance – the ORM-mapped instance being operated upon.

New in version 1.1.

See also

method sqlalchemy.orm.events.SessionEvents.loaded_as_persistent(session, instance)¶

Intercept the “loaded as persistent” transition for a specific object.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'loaded_as_persistent')
def receive_loaded_as_persistent(session, instance):
    "listen for the 'loaded_as_persistent' event"

    # ... (event handling logic) ...

This event is invoked within the ORM loading process, and is invoked very similarly to the InstanceEvents.load() event. However, the event here is linkable to a Session class or instance, rather than to a mapper or class hierarchy, and integrates with the other session lifecycle events smoothly. The object is guaranteed to be present in the session’s identity map when this event is called.

Note

This event is invoked within the loader process before eager loaders may have been completed, and the object’s state may not be complete. Additionally, invoking row-level refresh operations on the object will place the object into a new loader context, interfering with the existing load context. See the note on InstanceEvents.load() for background on making use of the SessionEvents.restore_load_context parameter, which works in the same manner as that of InstanceEvents.restore_load_context, in order to resolve this scenario.

Parameters:

session – target Session
instance – the ORM-mapped instance being operated upon.

New in version 1.1.

See also

method sqlalchemy.orm.events.SessionEvents.pending_to_persistent(session, instance)¶

Intercept the “pending to persistent”” transition for a specific object.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'pending_to_persistent')
def receive_pending_to_persistent(session, instance):
    "listen for the 'pending_to_persistent' event"

    # ... (event handling logic) ...

This event is invoked within the flush process, and is similar to scanning the Session.new collection within the SessionEvents.after_flush() event. However, in this case the object has already been moved to the persistent state when the event is called.

Parameters:

session – target Session
instance – the ORM-mapped instance being operated upon.

New in version 1.1.

See also

method sqlalchemy.orm.events.SessionEvents.pending_to_transient(session, instance)¶

Intercept the “pending to transient” transition for a specific object.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'pending_to_transient')
def receive_pending_to_transient(session, instance):
    "listen for the 'pending_to_transient' event"

    # ... (event handling logic) ...

This less common transition occurs when an pending object that has not been flushed is evicted from the session; this can occur when the Session.rollback() method rolls back the transaction, or when the Session.expunge() method is used.

Parameters:

session – target Session
instance – the ORM-mapped instance being operated upon.

New in version 1.1.

See also

method sqlalchemy.orm.events.SessionEvents.persistent_to_deleted(session, instance)¶

Intercept the “persistent to deleted” transition for a specific object.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'persistent_to_deleted')
def receive_persistent_to_deleted(session, instance):
    "listen for the 'persistent_to_deleted' event"

    # ... (event handling logic) ...

This event is invoked when a persistent object’s identity is deleted from the database within a flush, however the object still remains associated with the Session until the transaction completes.

If the transaction is rolled back, the object moves again to the persistent state, and the SessionEvents.deleted_to_persistent() event is called. If the transaction is committed, the object becomes detached, which will emit the SessionEvents.deleted_to_detached() event.

Note that while the Session.delete() method is the primary public interface to mark an object as deleted, many objects get deleted due to cascade rules, which are not always determined until flush time. Therefore, there’s no way to catch every object that will be deleted until the flush has proceeded. the SessionEvents.persistent_to_deleted() event is therefore invoked at the end of a flush.

New in version 1.1.

See also

method sqlalchemy.orm.events.SessionEvents.persistent_to_detached(session, instance)¶

Intercept the “persistent to detached” transition for a specific object.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'persistent_to_detached')
def receive_persistent_to_detached(session, instance):
    "listen for the 'persistent_to_detached' event"

    # ... (event handling logic) ...

This event is invoked when a persistent object is evicted from the session. There are many conditions that cause this to happen, including:

using a method such as Session.expunge() or Session.close()
Calling the Session.rollback() method, when the object was part of an INSERT statement for that session’s transaction

Parameters:

session – target Session
instance – the ORM-mapped instance being operated upon.
deleted – boolean. If True, indicates this object moved to the detached state because it was marked as deleted and flushed.

New in version 1.1.

See also

method sqlalchemy.orm.events.SessionEvents.persistent_to_transient(session, instance)¶

Intercept the “persistent to transient” transition for a specific object.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'persistent_to_transient')
def receive_persistent_to_transient(session, instance):
    "listen for the 'persistent_to_transient' event"

    # ... (event handling logic) ...

This less common transition occurs when an pending object that has has been flushed is evicted from the session; this can occur when the Session.rollback() method rolls back the transaction.

Parameters:

session – target Session
instance – the ORM-mapped instance being operated upon.

New in version 1.1.

See also

method sqlalchemy.orm.events.SessionEvents.transient_to_pending(session, instance)¶

Intercept the “transient to pending” transition for a specific object.

Example argument forms:

from sqlalchemy import event

# standard decorator style
@event.listens_for(SomeSessionOrFactory, 'transient_to_pending')
def receive_transient_to_pending(session, instance):
    "listen for the 'transient_to_pending' event"

    # ... (event handling logic) ...

This event is a specialization of the SessionEvents.after_attach() event which is only invoked for this specific transition. It is invoked typically during the Session.add() call.

Parameters:

session – target Session
instance – the ORM-mapped instance being operated upon.

New in version 1.1.

See also