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`, etc. **Create / Drop Events** Events emitted when CREATE and DROP commands are emitted to the database. The event hooks in this category include :meth:`.DDLEvents.before_create`, :meth:`.DDLEvents.after_create`, :meth:`.DDLEvents.before_drop`, and :meth:`.DDLEvents.after_drop`. These events are emitted when using schema-level methods such as :meth:`.MetaData.create_all` and :meth:`.MetaData.drop_all`. Per-object create/drop methods such as :meth:`.Table.create`, :meth:`.Table.drop`, :meth:`.Index.create` are also included, as well as dialect-specific methods such as :meth:`_postgresql.ENUM.create`. .. versionadded:: 2.0 :class:`.DDLEvents` event hooks now take place for non-table objects including constraints, indexes, and dialect-specific schema types. Event hooks may be attached directly to a :class:`_schema.Table` object or to a :class:`_schema.MetaData` collection, as well as to any :class:`.SchemaItem` class or object that can be individually created and dropped using a distinct SQL command. Such classes include :class:`.Index`, :class:`.Sequence`, and dialect-specific classes such as :class:`_postgresql.ENUM`. Example using the :meth:`.DDLEvents.after_create` event, where a custom event hook will emit an ``ALTER TABLE`` command on the current connection, after ``CREATE TABLE`` is emitted:: from sqlalchemy import create_engine from sqlalchemy import event from sqlalchemy import Table, Column, Metadata, Integer m = MetaData() some_table = Table('some_table', m, Column('data', Integer)) @event.listens_for(some_table, "after_create") def after_create(target, connection, **kw): connection.execute(text( "ALTER TABLE %s SET name=foo_%s" % (target.name, target.name) )) some_engine = create_engine("postgresql://scott:tiger@host/test") # will emit "CREATE TABLE some_table" as well as the above # "ALTER TABLE" statement afterwards m.create_all(some_engine) Constraint objects such as :class:`.ForeignKeyConstraint`, :class:`.UniqueConstraint`, :class:`.CheckConstraint` may also be subscribed to these events, however they will **not** normally produce events as these objects are usually rendered inline within an enclosing ``CREATE TABLE`` statement and implicitly dropped from a ``DROP TABLE`` statement. For the :class:`.Index` construct, the event hook will be emitted for ``CREATE INDEX``, however SQLAlchemy does not normally emit ``DROP INDEX`` when dropping tables as this is again implicit within the ``DROP TABLE`` statement. .. versionadded:: 2.0 Support for :class:`.SchemaItem` objects for create/drop events was expanded from its previous support for :class:`.MetaData` and :class:`.Table` to also include :class:`.Constraint` and all subclasses, :class:`.Index`, :class:`.Sequence` and some type-related constructs such as :class:`_postgresql.ENUM`. .. note:: These event hooks are only emitted within the scope of SQLAlchemy's create/drop methods; they are not necessarily supported by tools such as `alembic <https://alembic.sqlalchemy.org>`_. **Attachment Events** Attachment events are 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. These events include :meth:`.DDLEvents.before_parent_attach` and :meth:`.DDLEvents.after_parent_attach`. **Reflection Events** The :meth:`.DDLEvents.column_reflect` event is used to intercept and modify the in-Python definition of database columns when :term:`reflection` of database tables proceeds. **Use with Generic DDL** DDL events integrate closely with the :class:`.DDL` class and the :class:`.ExecutableDDLElement` 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") ) **Event Propagation to MetaData Copies** 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 metadata = MetaData() some_table = Table("some_table", metadata, Column("data", Integer)) event.listen( some_table, "after_create", DDL("ALTER TABLE %(table)s SET name=foo_%(table)s"), propagate=True ) new_metadata = MetaData() new_table = some_table.to_metadata(new_metadata) The above :class:`.DDL` object will be associated with the :meth:`.DDLEvents.after_create` event for both the ``some_table`` and the ``new_table`` :class:`.Table` objects. .. seealso:: :ref:`event_toplevel` :class:`.ExecutableDDLElement` :class:`.DDL` :ref:`schema_ddl_sequences`
| Method | after |
Called after CREATE statements are emitted. |
| Method | after |
Called after DROP statements are emitted. |
| Method | after |
Called after a :class:`.SchemaItem` is associated with a parent :class:`.SchemaItem`. |
| Method | before |
Called before CREATE statements are emitted. |
| Method | before |
Called before DROP statements are emitted. |
| Method | before |
Called before a :class:`.SchemaItem` is associated with a parent :class:`.SchemaItem`. |
| Method | column |
Called for each unit of 'column info' retrieved when a :class:`_schema.Table` is being reflected. |
| Method | _sa |
internal event hook used for primary key naming convention updates. |
| Class Variable | _target |
Undocumented |
Inherited from Events:
| Class Method | _accept |
Undocumented |
| Class Method | _clear |
Undocumented |
| Class Method | _listen |
Undocumented |
| Class Method | _remove |
Undocumented |
Inherited from _HasEventsDispatch (via Events):
| Method | __getattr__ |
Undocumented |
| Method | __init |
Intercept new Event subclasses and create associated _Dispatch classes. |
| Class Variable | dispatch |
reference back to the _Dispatch class. |
| Class Method | _create |
Create a :class:`._Dispatch` class corresponding to an :class:`.Events` class. |
| Static Method | _set |
Undocumented |
| Class Variable | _dispatch |
class which will receive the .dispatch collection |
Called after CREATE statements are emitted. :param target: the :class:`.SchemaObject`, such as a :class:`_schema.MetaData` or :class:`_schema.Table` but also including all create/drop objects such as :class:`.Index`, :class:`.Sequence`, etc., object which is the target of the event. .. versionadded:: 2.0 Support for all :class:`.SchemaItem` objects was added. :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.
Called after DROP statements are emitted. :param target: the :class:`.SchemaObject`, such as a :class:`_schema.MetaData` or :class:`_schema.Table` but also including all create/drop objects such as :class:`.Index`, :class:`.Sequence`, etc., object which is the target of the event. .. versionadded:: 2.0 Support for all :class:`.SchemaItem` objects was added. :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.
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.
Called before CREATE statements are emitted. :param target: the :class:`.SchemaObject`, such as a :class:`_schema.MetaData` or :class:`_schema.Table` but also including all create/drop objects such as :class:`.Index`, :class:`.Sequence`, etc., object which is the target of the event. .. versionadded:: 2.0 Support for all :class:`.SchemaItem` objects was added. :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.
Called before DROP statements are emitted. :param target: the :class:`.SchemaObject`, such as a :class:`_schema.MetaData` or :class:`_schema.Table` but also including all create/drop objects such as :class:`.Index`, :class:`.Sequence`, etc., object which is the target of the event. .. versionadded:: 2.0 Support for all :class:`.SchemaItem` objects was added. :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.
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.
Inspector, table: Table, column_info: ReflectedColumn):
(source)
¶
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