# sql/events.py
# Copyright (C) 2005-2024 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: https://www.opensource.org/licenses/mit-license.php
from .base import SchemaEventTarget
from .. import event
class DDLEvents(event.Events):
"""
Define event listeners for schema objects,
that is, :class:`.SchemaItem` and other :class:`.SchemaEventTarget`
subclasses, including :class:`_schema.MetaData`, :class:`_schema.Table`,
:class:`_schema.Column`.
:class:`_schema.MetaData` and :class:`_schema.Table` support events
specifically regarding when CREATE and DROP
DDL is emitted to the database.
Attachment events are also provided to customize
behavior whenever a child schema element is associated
with a parent, such as, when a :class:`_schema.Column` is associated
with its :class:`_schema.Table`, when a
:class:`_schema.ForeignKeyConstraint`
is associated with a :class:`_schema.Table`, etc.
Example using the ``after_create`` event::
from sqlalchemy import event
from sqlalchemy import Table, Column, Metadata, Integer
m = MetaData()
some_table = Table('some_table', m, Column('data', Integer))
def after_create(target, connection, **kw):
connection.execute(text(
"ALTER TABLE %s SET name=foo_%s" % (target.name, target.name)
))
event.listen(some_table, "after_create", after_create)
DDL events integrate closely with the
:class:`.DDL` class and the :class:`.DDLElement` hierarchy
of DDL clause constructs, which are themselves appropriate
as listener callables::
from sqlalchemy import DDL
event.listen(
some_table,
"after_create",
DDL("ALTER TABLE %(table)s SET name=foo_%(table)s")
)
The methods here define the name of an event as well
as the names of members that are passed to listener
functions.
For all :class:`.DDLEvent` events, the ``propagate=True`` keyword argument
will ensure that a given event handler is propagated to copies of the
object, which are made when using the :meth:`_schema.Table.to_metadata`
method::
from sqlalchemy import DDL
event.listen(
some_table,
"after_create",
DDL("ALTER TABLE %(table)s SET name=foo_%(table)s"),
propagate=True
)
new_table = some_table.to_metadata(new_metadata)
The above :class:`.DDL` object will also be associated with the
:class:`_schema.Table` object represented by ``new_table``.
.. seealso::
:ref:`event_toplevel`
:class:`.DDLElement`
:class:`.DDL`
:ref:`schema_ddl_sequences`
"""
_target_class_doc = "SomeSchemaClassOrObject"
_dispatch_target = SchemaEventTarget
def before_create(self, target, connection, **kw):
r"""Called before CREATE statements are emitted.
:param target: the :class:`_schema.MetaData` or :class:`_schema.Table`
object which is the target of the event.
:param connection: the :class:`_engine.Connection` where the
CREATE statement or statements will be emitted.
:param \**kw: additional keyword arguments relevant
to the event. The contents of this dictionary
may vary across releases, and include the
list of tables being generated for a metadata-level
event, the checkfirst flag, and other
elements used by internal events.
:func:`.event.listen` accepts the ``propagate=True``
modifier for this event; when True, the listener function will
be established for any copies made of the target object,
i.e. those copies that are generated when
:meth:`_schema.Table.to_metadata` is used.
:func:`.event.listen` accepts the ``insert=True``
modifier for this event; when True, the listener function will
be prepended to the internal list of events upon discovery, and execute
before registered listener functions that do not pass this argument.
"""
def after_create(self, target, connection, **kw):
r"""Called after CREATE statements are emitted.
:param target: the :class:`_schema.MetaData` or :class:`_schema.Table`
object which is the target of the event.
:param connection: the :class:`_engine.Connection` where the
CREATE statement or statements have been emitted.
:param \**kw: additional keyword arguments relevant
to the event. The contents of this dictionary
may vary across releases, and include the
list of tables being generated for a metadata-level
event, the checkfirst flag, and other
elements used by internal events.
:func:`.event.listen` also accepts the ``propagate=True``
modifier for this event; when True, the listener function will
be established for any copies made of the target object,
i.e. those copies that are generated when
:meth:`_schema.Table.to_metadata` is used.
"""
def before_drop(self, target, connection, **kw):
r"""Called before DROP statements are emitted.
:param target: the :class:`_schema.MetaData` or :class:`_schema.Table`
object which is the target of the event.
:param connection: the :class:`_engine.Connection` where the
DROP statement or statements will be emitted.
:param \**kw: additional keyword arguments relevant
to the event. The contents of this dictionary
may vary across releases, and include the
list of tables being generated for a metadata-level
event, the checkfirst flag, and other
elements used by internal events.
:func:`.event.listen` also accepts the ``propagate=True``
modifier for this event; when True, the listener function will
be established for any copies made of the target object,
i.e. those copies that are generated when
:meth:`_schema.Table.to_metadata` is used.
"""
def after_drop(self, target, connection, **kw):
r"""Called after DROP statements are emitted.
:param target: the :class:`_schema.MetaData` or :class:`_schema.Table`
object which is the target of the event.
:param connection: the :class:`_engine.Connection` where the
DROP statement or statements have been emitted.
:param \**kw: additional keyword arguments relevant
to the event. The contents of this dictionary
may vary across releases, and include the
list of tables being generated for a metadata-level
event, the checkfirst flag, and other
elements used by internal events.
:func:`.event.listen` also accepts the ``propagate=True``
modifier for this event; when True, the listener function will
be established for any copies made of the target object,
i.e. those copies that are generated when
:meth:`_schema.Table.to_metadata` is used.
"""
def before_parent_attach(self, target, parent):
"""Called before a :class:`.SchemaItem` is associated with
a parent :class:`.SchemaItem`.
:param target: the target object
:param parent: the parent to which the target is being attached.
:func:`.event.listen` also accepts the ``propagate=True``
modifier for this event; when True, the listener function will
be established for any copies made of the target object,
i.e. those copies that are generated when
:meth:`_schema.Table.to_metadata` is used.
"""
def after_parent_attach(self, target, parent):
"""Called after a :class:`.SchemaItem` is associated with
a parent :class:`.SchemaItem`.
:param target: the target object
:param parent: the parent to which the target is being attached.
:func:`.event.listen` also accepts the ``propagate=True``
modifier for this event; when True, the listener function will
be established for any copies made of the target object,
i.e. those copies that are generated when
:meth:`_schema.Table.to_metadata` is used.
"""
def _sa_event_column_added_to_pk_constraint(self, const, col):
"""internal event hook used for primary key naming convention
updates.
"""
def column_reflect(self, inspector, table, column_info):
"""Called for each unit of 'column info' retrieved when
a :class:`_schema.Table` is being reflected.
This event is most easily used by applying it to a specific
:class:`_schema.MetaData` instance, where it will take effect for
all :class:`_schema.Table` objects within that
:class:`_schema.MetaData` that undergo reflection::
metadata = MetaData()
@event.listens_for(metadata, 'column_reflect')
def receive_column_reflect(inspector, table, column_info):
# receives for all Table objects that are reflected
# under this MetaData
# will use the above event hook
my_table = Table("my_table", metadata, autoload_with=some_engine)
.. versionadded:: 1.4.0b2 The :meth:`_events.DDLEvents.column_reflect`
hook may now be applied to a :class:`_schema.MetaData` object as
well as the :class:`_schema.MetaData` class itself where it will
take place for all :class:`_schema.Table` objects associated with
the targeted :class:`_schema.MetaData`.
It may also be applied to the :class:`_schema.Table` class across
the board::
from sqlalchemy import Table
@event.listens_for(Table, 'column_reflect')
def receive_column_reflect(inspector, table, column_info):
# receives for all Table objects that are reflected
It can also be applied to a specific :class:`_schema.Table` at the
point that one is being reflected using the
:paramref:`_schema.Table.listeners` parameter::
t1 = Table(
"my_table",
autoload_with=some_engine,
listeners=[
('column_reflect', receive_column_reflect)
]
)
The dictionary of column information as returned by the
dialect is passed, and can be modified. The dictionary
is that returned in each element of the list returned
by :meth:`.reflection.Inspector.get_columns`:
* ``name`` - the column's name, is applied to the
:paramref:`_schema.Column.name` parameter
* ``type`` - the type of this column, which should be an instance
of :class:`~sqlalchemy.types.TypeEngine`, is applied to the
:paramref:`_schema.Column.type` parameter
* ``nullable`` - boolean flag if the column is NULL or NOT NULL,
is applied to the :paramref:`_schema.Column.nullable` parameter
* ``default`` - the column's server default value. This is
normally specified as a plain string SQL expression, however the
event can pass a :class:`.FetchedValue`, :class:`.DefaultClause`,
or :func:`_expression.text` object as well. Is applied to the
:paramref:`_schema.Column.server_default` parameter
The event is called before any action is taken against
this dictionary, and the contents can be modified; the following
additional keys may be added to the dictionary to further modify
how the :class:`_schema.Column` is constructed:
* ``key`` - the string key that will be used to access this
:class:`_schema.Column` in the ``.c`` collection; will be applied
to the :paramref:`_schema.Column.key` parameter. Is also used
for ORM mapping. See the section
:ref:`mapper_automated_reflection_schemes` for an example.
* ``quote`` - force or un-force quoting on the column name;
is applied to the :paramref:`_schema.Column.quote` parameter.
* ``info`` - a dictionary of arbitrary data to follow along with
the :class:`_schema.Column`, is applied to the
:paramref:`_schema.Column.info` parameter.
:func:`.event.listen` also accepts the ``propagate=True``
modifier for this event; when True, the listener function will
be established for any copies made of the target object,
i.e. those copies that are generated when
:meth:`_schema.Table.to_metadata` is used.
.. seealso::
:ref:`mapper_automated_reflection_schemes` -
in the ORM mapping documentation
:ref:`automap_intercepting_columns` -
in the :ref:`automap_toplevel` documentation
:ref:`metadata_reflection_dbagnostic_types` - in
the :ref:`metadata_reflection_toplevel` documentation
"""
