The ORM includes a wide variety of hooks available for subscription.
New in version 0.7: The event supersedes the previous system of “extension” classes.
For an introduction to the event API, see Events. Non-ORM events such as those regarding connections and low-level statement execution are described in Core Events.
Bases: sqlalchemy.event.base.Events
Define events for object attributes.
These are typically defined on the class-bound descriptor for the target class.
e.g.:
from sqlalchemy import event
def my_append_listener(target, value, initiator):
print "received append event for target: %s" % target
event.listen(MyClass.collection, 'append', my_append_listener)Listeners have the option to return a possibly modified version of the value, when the retval=True flag is passed to listen():
def validate_phone(target, value, oldvalue, initiator):
"Strip non-numeric characters from a phone number"
return re.sub(r'(?![0-9])', '', value)
# setup listener on UserContact.phone attribute, instructing
# it to use the return value
listen(UserContact.phone, 'set', validate_phone, retval=True)A validation function like the above can also raise an exception such as ValueError to halt the operation.
Several modifiers are available to the listen() function.
| Parameters: |
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Receive a collection append event.
Example argument forms:
from sqlalchemy import event
# standard decorator style
@event.listens_for(SomeClass.some_attribute, 'append')
def receive_append(target, value, initiator):
"listen for the 'append' event"
# ... (event handling logic) ...| Parameters: |
|
|---|---|
| Returns: | if the event was registered with retval=True, the given value, or a new effective value, should be returned. |
Receive a collection remove event.
Example argument forms:
from sqlalchemy import event
# standard decorator style
@event.listens_for(SomeClass.some_attribute, 'remove')
def receive_remove(target, value, initiator):
"listen for the 'remove' event"
# ... (event handling logic) ...| Parameters: |
|
|---|---|
| Returns: | No return value is defined for this event. |
Receive a scalar set event.
Example argument forms:
from sqlalchemy import event
# standard decorator style
@event.listens_for(SomeClass.some_attribute, 'set')
def receive_set(target, value, oldvalue, initiator):
"listen for the 'set' event"
# ... (event handling logic) ...
# named argument style (new in 0.9)
@event.listens_for(SomeClass.some_attribute, 'set', named=True)
def receive_set(**kw):
"listen for the 'set' event"
target = kw['target']
value = kw['value']
# ... (event handling logic) ...| Parameters: |
|
|---|---|
| Returns: | if the event was registered with retval=True, the given value, or a new effective value, should be returned. |
Bases: sqlalchemy.event.base.Events
Define events specific to mappings.
e.g.:
from sqlalchemy import event
def my_before_insert_listener(mapper, connection, target):
# execute a stored procedure upon INSERT,
# apply the value to the row to be inserted
target.calculated_value = connection.scalar(
"select my_special_function(%d)"
% target.special_number)
# associate the listener function with SomeClass,
# to execute during the "before_insert" hook
event.listen(
SomeClass, 'before_insert', my_before_insert_listener)Available targets include:
Changed in version 0.8.0: mapper events can be associated with unmapped superclasses of mapped classes.
Mapper events provide hooks into critical sections of the mapper, including those related to object instrumentation, object loading, and object persistence. In particular, the persistence methods before_insert(), and before_update() are popular places to augment the state being persisted - however, these methods operate with several significant restrictions. The user is encouraged to evaluate the SessionEvents.before_flush() and SessionEvents.after_flush() methods as more flexible and user-friendly hooks in which to apply additional database state during a flush.
When using MapperEvents, several modifiers are available to the event.listen() function.
| Parameters: |
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Called after a series of mappers have been configured.
Example argument forms:
from sqlalchemy import event
# standard decorator style
@event.listens_for(SomeClass, 'after_configured')
def receive_after_configured():
"listen for the 'after_configured' event"
# ... (event handling logic) ...This corresponds to the orm.configure_mappers() call, which note is usually called automatically as mappings are first used.
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, "after_configured")
def go():
# ...
Theoretically this event is called once per application, but is actually called any time new mappers have been affected by a orm.configure_mappers() call. If new mappings are constructed after existing ones have already been used, this event can 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, "after_configured", once=True)
def go():
# ...
Receive an object instance after a DELETE statement has been emitted corresponding to that instance.
Example argument forms:
from sqlalchemy import event
# standard decorator style
@event.listens_for(SomeClass, 'after_delete')
def receive_after_delete(mapper, connection, target):
"listen for the 'after_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 after their DELETE statements have been emitted at once in a previous step.
Warning
Mapper-level flush events are designed to operate on attributes local to the immediate object being handled and via SQL operations with the given Connection only. Handlers here should not make alterations to the state of the Session overall, and in general should not affect any relationship() -mapped attributes, as session cascade rules will not function properly, nor is it always known if the related class has already been handled. Operations that are not supported in mapper events include:
Operations which manipulate the state of the object relative to other objects are better handled:
| Parameters: |
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|---|---|
| Returns: | No return value is supported by this event. |
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 are designed to operate on attributes local to the immediate object being handled and via SQL operations with the given Connection only. Handlers here should not make alterations to the state of the Session overall, and in general should not affect any relationship() -mapped attributes, as session cascade rules will not function properly, nor is it always known if the related class has already been handled. Operations that are not supported in mapper events include:
Operations which manipulate the state of the object relative to other objects are better handled:
| Parameters: |
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|---|---|
| Returns: | No return value is supported by this event. |
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 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 are designed to operate on attributes local to the immediate object being handled and via SQL operations with the given Connection only. Handlers here should not make alterations to the state of the Session overall, and in general should not affect any relationship() -mapped attributes, as session cascade rules will not function properly, nor is it always known if the related class has already been handled. Operations that are not supported in mapper events include:
Operations which manipulate the state of the object relative to other objects are better handled:
| Parameters: |
|
|---|---|
| Returns: | No return value is supported by this event. |
Receive an object instance before that instance is appended to a result list.
Example argument forms:
from sqlalchemy import event
# standard decorator style
@event.listens_for(SomeClass, 'append_result')
def receive_append_result(mapper, context, row, target, result, **kw):
"listen for the 'append_result' event"
# ... (event handling logic) ...
# named argument style (new in 0.9)
@event.listens_for(SomeClass, 'append_result', named=True)
def receive_append_result(**kw):
"listen for the 'append_result' event"
mapper = kw['mapper']
context = kw['context']
# ... (event handling logic) ...Deprecated since version 0.9: the append_result() event should be considered as legacy. It is a difficult to use method whose original purpose is better suited by custom collection classes.
This is a rarely used hook which can be used to alter the construction of a result list returned by Query.
| Parameters: |
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| Returns: | If this method is registered with retval=True, a return value of EXT_STOP will prevent the instance from being appended to the given result list, whereas a return value of EXT_CONTINUE will result in the default behavior of appending the value to the result list. |
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) ...This corresponds to the orm.configure_mappers() call, which note is usually called automatically as mappings are first used.
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():
# ...
Theoretically this event is called once per application, but is actually called any time new mappers are to be affected by a orm.configure_mappers() call. If new mappings are constructed after existing ones have already been used, this event can 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.
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 are designed to operate on attributes local to the immediate object being handled and via SQL operations with the given Connection only. Handlers here should not make alterations to the state of the Session overall, and in general should not affect any relationship() -mapped attributes, as session cascade rules will not function properly, nor is it always known if the related class has already been handled. Operations that are not supported in mapper events include:
Operations which manipulate the state of the object relative to other objects are better handled:
| Parameters: |
|
|---|---|
| Returns: | No return value is supported by this event. |
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 are designed to operate on attributes local to the immediate object being handled and via SQL operations with the given Connection only. Handlers here should not make alterations to the state of the Session overall, and in general should not affect any relationship() -mapped attributes, as session cascade rules will not function properly, nor is it always known if the related class has already been handled. Operations that are not supported in mapper events include:
Operations which manipulate the state of the object relative to other objects are better handled:
| Parameters: |
|
|---|---|
| Returns: | No return value is supported by this event. |
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 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 are designed to operate on attributes local to the immediate object being handled and via SQL operations with the given Connection only. Handlers here should not make alterations to the state of the Session overall, and in general should not affect any relationship() -mapped attributes, as session cascade rules will not function properly, nor is it always known if the related class has already been handled. Operations that are not supported in mapper events include:
Operations which manipulate the state of the object relative to other objects are better handled:
| Parameters: |
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|---|---|
| Returns: | No return value is supported by this event. |
Receive a row when a new object instance is about to be created from that row.
Example argument forms:
from sqlalchemy import event
# standard decorator style
@event.listens_for(SomeClass, 'create_instance')
def receive_create_instance(mapper, context, row, class_):
"listen for the 'create_instance' event"
# ... (event handling logic) ...
# named argument style (new in 0.9)
@event.listens_for(SomeClass, 'create_instance', named=True)
def receive_create_instance(**kw):
"listen for the 'create_instance' event"
mapper = kw['mapper']
context = kw['context']
# ... (event handling logic) ...Deprecated since version 0.9: the create_instance() event should be considered as legacy. Manipulation of the object construction mechanics during a load should not be necessary.
The method can choose to create the instance itself, or it can return EXT_CONTINUE to indicate normal object creation should take place. This listener is typically registered with retval=True.
| Parameters: |
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|---|---|
| Returns: | When configured with retval=True, the return value should be a newly created instance of the mapped class, or EXT_CONTINUE indicating that default object construction should take place. |
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: |
|---|
Called when the mapper for the class is fully configured.
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) ...This event is the latest phase of mapper construction, and is invoked when the mapped classes are first used, so that relationships between mappers can be resolved. When the event is called, the mapper should be in its final state.
While the configuration event normally occurs automatically, it can be forced to occur ahead of time, in the case where the event is needed before any actual mapper usage, by using the configure_mappers() function.
| Parameters: |
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Receive an instance before that instance has its attributes populated.
Example argument forms:
from sqlalchemy import event
# standard decorator style
@event.listens_for(SomeClass, 'populate_instance')
def receive_populate_instance(mapper, context, row, target, **kw):
"listen for the 'populate_instance' event"
# ... (event handling logic) ...
# named argument style (new in 0.9)
@event.listens_for(SomeClass, 'populate_instance', named=True)
def receive_populate_instance(**kw):
"listen for the 'populate_instance' event"
mapper = kw['mapper']
context = kw['context']
# ... (event handling logic) ...Deprecated since version 0.9: the populate_instance() event should be considered as legacy. The mechanics of instance population should not need modification; special “on load” rules can as always be accommodated by the InstanceEvents.load event.
This usually corresponds to a newly loaded instance but may also correspond to an already-loaded instance which has unloaded attributes to be populated. The method may be called many times for a single instance, as multiple result rows are used to populate eagerly loaded collections.
Most usages of this hook are obsolete. For a generic “object has been newly created from a row” hook, use InstanceEvents.load().
| Parameters: |
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| Returns: | When configured with retval=True, a return value of EXT_STOP will bypass instance population by the mapper. A value of EXT_CONTINUE indicates that default instance population should take place. |
Perform pre-processing on the given result row and return a new row instance.
Example argument forms:
from sqlalchemy import event
# standard decorator style
@event.listens_for(SomeClass, 'translate_row')
def receive_translate_row(mapper, context, row):
"listen for the 'translate_row' event"
# ... (event handling logic) ...Deprecated since version 0.9: the translate_row() event should be considered as legacy. The row as delivered in a mapper load operation typically requires that highly technical details be accommodated in order to identity the correct column keys are present in the row, rendering this particular event hook as difficult to use and unreliable.
This listener is typically registered with retval=True. It is called when the mapper first receives a row, before the object identity or the instance itself has been derived from that row. The given row may or may not be a RowProxy object - it will always be a dictionary-like object which contains mapped columns as keys. The returned object should also be a dictionary-like object which recognizes mapped columns as keys.
| Parameters: |
|
|---|---|
| Returns: | When configured with retval=True, the function should return a dictionary-like row object, or EXT_CONTINUE, indicating the original row should be used. |
Bases: sqlalchemy.event.base.Events
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:
Changed in version 0.8.0: instance events can be associated with unmapped superclasses of mapped classes.
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 event.listen() function.
| Parameters: |
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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: |
|
|---|
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) ...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. It is not called when an object is loaded from the database.
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. It is not called when an object is loaded from the database.
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.
Note that during a result-row load, this method is called upon the first row received for this instance. Note that some attributes and collections may or may not be loaded or even initialized, depending on what’s present in the result rows.
| Parameters: |
|
|---|
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: |
|
|---|
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) ...| Parameters: |
|
|---|
Receive an object instance as it is ‘resurrected’ from garbage collection, which occurs when a “dirty” state falls out of scope.
Example argument forms:
from sqlalchemy import event
# standard decorator style
@event.listens_for(SomeClass, 'resurrect')
def receive_resurrect(target):
"listen for the 'resurrect' 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. |
|---|
Deprecated since version 0.9: - the resurrect event has no function, as the underlying functionality was dependent on the “mutation tracking” feature removed from SQLAlchemy in the 0.8 series. This event is removed in 1.0.
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: |
|
|---|
Bases: sqlalchemy.event.base.Events
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.
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
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: |
|
|---|
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) ...
# legacy calling style (pre-0.9)
@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) ...Changed in version 0.9: The after_bulk_delete event now accepts the arguments delete_context. Listener functions which accept the previous argument signature(s) listed above will be automatically adapted to the new signature.
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:
|
|---|
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) ...
# legacy calling style (pre-0.9)
@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) ...Changed in version 0.9: The after_bulk_update event now accepts the arguments update_context. Listener functions which accept the previous argument signature(s) listed above will be automatically adapted to the new signature.
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:
|
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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 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 before_flush(), after_flush(), or after_flush_postexec() events.
Note
The Session is not in an active transaction when the after_commit() event is invoked, and therefore can not emit SQL. To emit SQL corresponding to every transaction, use the before_commit() event.
| Parameters: | session¶ – The target Session. |
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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.
| Parameters: |
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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: |
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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. |
|---|
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: |
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New in version 0.7.3.
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 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 after_transaction_end() event (assuming normal operation of the Session).
| Parameters: |
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New in version 0.8.
See also
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 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 after_transaction_create() event.
| Parameters: |
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New in version 0.8.
See also
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.
New in version 0.8.: Note that after_attach() now fires off after the item is part of the session. before_attach() is provided for those cases where the item should not yet be part of the session state.
See also
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 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 before_flush(), after_flush(), or after_flush_postexec() events.
| Parameters: | session¶ – The target Session. |
|---|
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: |
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Defines SQLAlchemy’s system of class instrumentation.
This module is usually not directly visible to user applications, but defines a large part of the ORM’s interactivity.
instrumentation.py deals with registration of end-user classes for state tracking. It interacts closely with state.py and attributes.py which establish per-instance and per-class-attribute instrumentation, respectively.
The class instrumentation system can be customized on a per-class or global basis using the sqlalchemy.ext.instrumentation module, which provides the means to build and specify alternate instrumentation forms.
Bases: sqlalchemy.event.base.Events
Events related to class instrumentation events.
The listeners here support being established against any new style class, that is any object that is a subclass of ‘type’. Events will then be fired off for events against that class. If the “propagate=True” flag is passed to event.listen(), the event will fire off for subclasses of that class as well.
The Python type builtin is also accepted as a target, which when used has the effect of events being emitted for all classes.
Note the “propagate” flag here is defaulted to True, unlike the other class level events where it defaults to False. This means that new subclasses will also be the subject of these events, when a listener is established on a superclass.
Changed in version 0.8: - events here will emit based on comparing the incoming class to the type of class passed to event.listen(). Previously, the event would fire for any class unconditionally regardless of what class was sent for listening, despite documentation which stated the contrary.
Example argument forms:
from sqlalchemy import event
# standard decorator style
@event.listens_for(SomeBaseClass, 'attribute_instrument')
def receive_attribute_instrument(cls, key, inst):
"listen for the 'attribute_instrument' event"
# ... (event handling logic) ...Called when an attribute is instrumented.
Called after the given class is instrumented.
Example argument forms:
from sqlalchemy import event
# standard decorator style
@event.listens_for(SomeBaseClass, 'class_instrument')
def receive_class_instrument(cls):
"listen for the 'class_instrument' event"
# ... (event handling logic) ...To get at the ClassManager, use manager_of_class().
Called before the given class is uninstrumented.
Example argument forms:
from sqlalchemy import event
# standard decorator style
@event.listens_for(SomeBaseClass, 'class_uninstrument')
def receive_class_uninstrument(cls):
"listen for the 'class_uninstrument' event"
# ... (event handling logic) ...To get at the ClassManager, use manager_of_class().