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456 lines
18 KiB
456 lines
18 KiB
# sqlalchemy/sql/events.py
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# Copyright (C) 2005-2023 the SQLAlchemy authors and contributors
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# <see AUTHORS file>
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#
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# This module is part of SQLAlchemy and is released under
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# the MIT License: https://www.opensource.org/licenses/mit-license.php
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from __future__ import annotations
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from typing import Any
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from typing import TYPE_CHECKING
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from .base import SchemaEventTarget
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from .. import event
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if TYPE_CHECKING:
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from .schema import Column
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from .schema import Constraint
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from .schema import SchemaItem
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from .schema import Table
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from ..engine.base import Connection
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from ..engine.interfaces import ReflectedColumn
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from ..engine.reflection import Inspector
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class DDLEvents(event.Events[SchemaEventTarget]):
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"""
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Define event listeners for schema objects,
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that is, :class:`.SchemaItem` and other :class:`.SchemaEventTarget`
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subclasses, including :class:`_schema.MetaData`, :class:`_schema.Table`,
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:class:`_schema.Column`, etc.
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**Create / Drop Events**
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Events emitted when CREATE and DROP commands are emitted to the database.
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The event hooks in this category include :meth:`.DDLEvents.before_create`,
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:meth:`.DDLEvents.after_create`, :meth:`.DDLEvents.before_drop`, and
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:meth:`.DDLEvents.after_drop`.
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These events are emitted when using schema-level methods such as
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:meth:`.MetaData.create_all` and :meth:`.MetaData.drop_all`. Per-object
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create/drop methods such as :meth:`.Table.create`, :meth:`.Table.drop`,
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:meth:`.Index.create` are also included, as well as dialect-specific
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methods such as :meth:`_postgresql.ENUM.create`.
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.. versionadded:: 2.0 :class:`.DDLEvents` event hooks now take place
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for non-table objects including constraints, indexes, and
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dialect-specific schema types.
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Event hooks may be attached directly to a :class:`_schema.Table` object or
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to a :class:`_schema.MetaData` collection, as well as to any
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:class:`.SchemaItem` class or object that can be individually created and
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dropped using a distinct SQL command. Such classes include :class:`.Index`,
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:class:`.Sequence`, and dialect-specific classes such as
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:class:`_postgresql.ENUM`.
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Example using the :meth:`.DDLEvents.after_create` event, where a custom
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event hook will emit an ``ALTER TABLE`` command on the current connection,
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after ``CREATE TABLE`` is emitted::
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from sqlalchemy import create_engine
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from sqlalchemy import event
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from sqlalchemy import Table, Column, Metadata, Integer
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m = MetaData()
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some_table = Table('some_table', m, Column('data', Integer))
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@event.listens_for(some_table, "after_create")
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def after_create(target, connection, **kw):
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connection.execute(text(
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"ALTER TABLE %s SET name=foo_%s" % (target.name, target.name)
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))
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some_engine = create_engine("postgresql://scott:tiger@host/test")
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# will emit "CREATE TABLE some_table" as well as the above
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# "ALTER TABLE" statement afterwards
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m.create_all(some_engine)
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Constraint objects such as :class:`.ForeignKeyConstraint`,
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:class:`.UniqueConstraint`, :class:`.CheckConstraint` may also be
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subscribed to these events, however they will **not** normally produce
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events as these objects are usually rendered inline within an
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enclosing ``CREATE TABLE`` statement and implicitly dropped from a
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``DROP TABLE`` statement.
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For the :class:`.Index` construct, the event hook will be emitted
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for ``CREATE INDEX``, however SQLAlchemy does not normally emit
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``DROP INDEX`` when dropping tables as this is again implicit within the
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``DROP TABLE`` statement.
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.. versionadded:: 2.0 Support for :class:`.SchemaItem` objects
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for create/drop events was expanded from its previous support for
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:class:`.MetaData` and :class:`.Table` to also include
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:class:`.Constraint` and all subclasses, :class:`.Index`,
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:class:`.Sequence` and some type-related constructs such as
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:class:`_postgresql.ENUM`.
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.. note:: These event hooks are only emitted within the scope of
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SQLAlchemy's create/drop methods; they are not necessarily supported
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by tools such as `alembic <https://alembic.sqlalchemy.org>`_.
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**Attachment Events**
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Attachment events are provided to customize
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behavior whenever a child schema element is associated
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with a parent, such as when a :class:`_schema.Column` is associated
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with its :class:`_schema.Table`, when a
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:class:`_schema.ForeignKeyConstraint`
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is associated with a :class:`_schema.Table`, etc. These events include
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:meth:`.DDLEvents.before_parent_attach` and
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:meth:`.DDLEvents.after_parent_attach`.
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**Reflection Events**
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The :meth:`.DDLEvents.column_reflect` event is used to intercept
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and modify the in-Python definition of database columns when
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:term:`reflection` of database tables proceeds.
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**Use with Generic DDL**
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DDL events integrate closely with the
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:class:`.DDL` class and the :class:`.ExecutableDDLElement` hierarchy
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of DDL clause constructs, which are themselves appropriate
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as listener callables::
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from sqlalchemy import DDL
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event.listen(
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some_table,
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"after_create",
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DDL("ALTER TABLE %(table)s SET name=foo_%(table)s")
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)
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**Event Propagation to MetaData Copies**
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For all :class:`.DDLEvent` events, the ``propagate=True`` keyword argument
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will ensure that a given event handler is propagated to copies of the
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object, which are made when using the :meth:`_schema.Table.to_metadata`
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method::
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from sqlalchemy import DDL
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metadata = MetaData()
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some_table = Table("some_table", metadata, Column("data", Integer))
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event.listen(
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some_table,
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"after_create",
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DDL("ALTER TABLE %(table)s SET name=foo_%(table)s"),
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propagate=True
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)
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new_metadata = MetaData()
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new_table = some_table.to_metadata(new_metadata)
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The above :class:`.DDL` object will be associated with the
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:meth:`.DDLEvents.after_create` event for both the ``some_table`` and
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the ``new_table`` :class:`.Table` objects.
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.. seealso::
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:ref:`event_toplevel`
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:class:`.ExecutableDDLElement`
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:class:`.DDL`
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:ref:`schema_ddl_sequences`
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"""
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_target_class_doc = "SomeSchemaClassOrObject"
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_dispatch_target = SchemaEventTarget
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def before_create(
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self, target: SchemaEventTarget, connection: Connection, **kw: Any
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) -> None:
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r"""Called before CREATE statements are emitted.
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:param target: the :class:`.SchemaObject`, such as a
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:class:`_schema.MetaData` or :class:`_schema.Table`
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but also including all create/drop objects such as
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:class:`.Index`, :class:`.Sequence`, etc.,
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object which is the target of the event.
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.. versionadded:: 2.0 Support for all :class:`.SchemaItem` objects
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was added.
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:param connection: the :class:`_engine.Connection` where the
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CREATE statement or statements will be emitted.
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:param \**kw: additional keyword arguments relevant
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to the event. The contents of this dictionary
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may vary across releases, and include the
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list of tables being generated for a metadata-level
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event, the checkfirst flag, and other
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elements used by internal events.
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:func:`.event.listen` accepts the ``propagate=True``
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modifier for this event; when True, the listener function will
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be established for any copies made of the target object,
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i.e. those copies that are generated when
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:meth:`_schema.Table.to_metadata` is used.
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:func:`.event.listen` accepts the ``insert=True``
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modifier for this event; when True, the listener function will
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be prepended to the internal list of events upon discovery, and execute
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before registered listener functions that do not pass this argument.
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"""
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def after_create(
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self, target: SchemaEventTarget, connection: Connection, **kw: Any
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) -> None:
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r"""Called after CREATE statements are emitted.
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:param target: the :class:`.SchemaObject`, such as a
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:class:`_schema.MetaData` or :class:`_schema.Table`
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but also including all create/drop objects such as
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:class:`.Index`, :class:`.Sequence`, etc.,
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object which is the target of the event.
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.. versionadded:: 2.0 Support for all :class:`.SchemaItem` objects
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was added.
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:param connection: the :class:`_engine.Connection` where the
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CREATE statement or statements have been emitted.
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:param \**kw: additional keyword arguments relevant
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to the event. The contents of this dictionary
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may vary across releases, and include the
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list of tables being generated for a metadata-level
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event, the checkfirst flag, and other
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elements used by internal events.
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:func:`.event.listen` also accepts the ``propagate=True``
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modifier for this event; when True, the listener function will
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be established for any copies made of the target object,
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i.e. those copies that are generated when
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:meth:`_schema.Table.to_metadata` is used.
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"""
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def before_drop(
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self, target: SchemaEventTarget, connection: Connection, **kw: Any
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) -> None:
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r"""Called before DROP statements are emitted.
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:param target: the :class:`.SchemaObject`, such as a
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:class:`_schema.MetaData` or :class:`_schema.Table`
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but also including all create/drop objects such as
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:class:`.Index`, :class:`.Sequence`, etc.,
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object which is the target of the event.
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.. versionadded:: 2.0 Support for all :class:`.SchemaItem` objects
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was added.
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:param connection: the :class:`_engine.Connection` where the
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DROP statement or statements will be emitted.
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:param \**kw: additional keyword arguments relevant
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to the event. The contents of this dictionary
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may vary across releases, and include the
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list of tables being generated for a metadata-level
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event, the checkfirst flag, and other
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elements used by internal events.
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:func:`.event.listen` also accepts the ``propagate=True``
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modifier for this event; when True, the listener function will
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be established for any copies made of the target object,
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i.e. those copies that are generated when
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:meth:`_schema.Table.to_metadata` is used.
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"""
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def after_drop(
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self, target: SchemaEventTarget, connection: Connection, **kw: Any
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) -> None:
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r"""Called after DROP statements are emitted.
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:param target: the :class:`.SchemaObject`, such as a
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:class:`_schema.MetaData` or :class:`_schema.Table`
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but also including all create/drop objects such as
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:class:`.Index`, :class:`.Sequence`, etc.,
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object which is the target of the event.
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.. versionadded:: 2.0 Support for all :class:`.SchemaItem` objects
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was added.
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:param connection: the :class:`_engine.Connection` where the
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DROP statement or statements have been emitted.
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:param \**kw: additional keyword arguments relevant
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to the event. The contents of this dictionary
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may vary across releases, and include the
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list of tables being generated for a metadata-level
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event, the checkfirst flag, and other
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elements used by internal events.
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:func:`.event.listen` also accepts the ``propagate=True``
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modifier for this event; when True, the listener function will
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be established for any copies made of the target object,
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i.e. those copies that are generated when
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:meth:`_schema.Table.to_metadata` is used.
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"""
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def before_parent_attach(
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self, target: SchemaEventTarget, parent: SchemaItem
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) -> None:
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"""Called before a :class:`.SchemaItem` is associated with
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a parent :class:`.SchemaItem`.
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:param target: the target object
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:param parent: the parent to which the target is being attached.
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:func:`.event.listen` also accepts the ``propagate=True``
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modifier for this event; when True, the listener function will
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be established for any copies made of the target object,
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i.e. those copies that are generated when
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:meth:`_schema.Table.to_metadata` is used.
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"""
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def after_parent_attach(
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self, target: SchemaEventTarget, parent: SchemaItem
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) -> None:
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"""Called after a :class:`.SchemaItem` is associated with
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a parent :class:`.SchemaItem`.
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:param target: the target object
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:param parent: the parent to which the target is being attached.
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:func:`.event.listen` also accepts the ``propagate=True``
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modifier for this event; when True, the listener function will
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be established for any copies made of the target object,
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i.e. those copies that are generated when
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:meth:`_schema.Table.to_metadata` is used.
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"""
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def _sa_event_column_added_to_pk_constraint(
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self, const: Constraint, col: Column[Any]
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) -> None:
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"""internal event hook used for primary key naming convention
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updates.
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"""
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def column_reflect(
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self, inspector: Inspector, table: Table, column_info: ReflectedColumn
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) -> None:
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"""Called for each unit of 'column info' retrieved when
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a :class:`_schema.Table` is being reflected.
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This event is most easily used by applying it to a specific
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:class:`_schema.MetaData` instance, where it will take effect for
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all :class:`_schema.Table` objects within that
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:class:`_schema.MetaData` that undergo reflection::
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metadata = MetaData()
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@event.listens_for(metadata, 'column_reflect')
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def receive_column_reflect(inspector, table, column_info):
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# receives for all Table objects that are reflected
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# under this MetaData
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# will use the above event hook
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my_table = Table("my_table", metadata, autoload_with=some_engine)
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.. versionadded:: 1.4.0b2 The :meth:`_events.DDLEvents.column_reflect`
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hook may now be applied to a :class:`_schema.MetaData` object as
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well as the :class:`_schema.MetaData` class itself where it will
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take place for all :class:`_schema.Table` objects associated with
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the targeted :class:`_schema.MetaData`.
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It may also be applied to the :class:`_schema.Table` class across
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the board::
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from sqlalchemy import Table
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@event.listens_for(Table, 'column_reflect')
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def receive_column_reflect(inspector, table, column_info):
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# receives for all Table objects that are reflected
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It can also be applied to a specific :class:`_schema.Table` at the
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point that one is being reflected using the
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:paramref:`_schema.Table.listeners` parameter::
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t1 = Table(
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"my_table",
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autoload_with=some_engine,
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listeners=[
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('column_reflect', receive_column_reflect)
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]
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)
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The dictionary of column information as returned by the
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dialect is passed, and can be modified. The dictionary
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is that returned in each element of the list returned
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by :meth:`.reflection.Inspector.get_columns`:
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* ``name`` - the column's name, is applied to the
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:paramref:`_schema.Column.name` parameter
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* ``type`` - the type of this column, which should be an instance
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of :class:`~sqlalchemy.types.TypeEngine`, is applied to the
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:paramref:`_schema.Column.type` parameter
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* ``nullable`` - boolean flag if the column is NULL or NOT NULL,
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is applied to the :paramref:`_schema.Column.nullable` parameter
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* ``default`` - the column's server default value. This is
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normally specified as a plain string SQL expression, however the
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event can pass a :class:`.FetchedValue`, :class:`.DefaultClause`,
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or :func:`_expression.text` object as well. Is applied to the
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:paramref:`_schema.Column.server_default` parameter
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The event is called before any action is taken against
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this dictionary, and the contents can be modified; the following
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additional keys may be added to the dictionary to further modify
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how the :class:`_schema.Column` is constructed:
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* ``key`` - the string key that will be used to access this
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:class:`_schema.Column` in the ``.c`` collection; will be applied
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to the :paramref:`_schema.Column.key` parameter. Is also used
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for ORM mapping. See the section
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:ref:`mapper_automated_reflection_schemes` for an example.
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* ``quote`` - force or un-force quoting on the column name;
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is applied to the :paramref:`_schema.Column.quote` parameter.
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* ``info`` - a dictionary of arbitrary data to follow along with
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the :class:`_schema.Column`, is applied to the
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:paramref:`_schema.Column.info` parameter.
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:func:`.event.listen` also accepts the ``propagate=True``
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modifier for this event; when True, the listener function will
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be established for any copies made of the target object,
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i.e. those copies that are generated when
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:meth:`_schema.Table.to_metadata` is used.
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.. seealso::
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:ref:`mapper_automated_reflection_schemes` -
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in the ORM mapping documentation
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:ref:`automap_intercepting_columns` -
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in the :ref:`automap_toplevel` documentation
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:ref:`metadata_reflection_dbagnostic_types` - in
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the :ref:`metadata_reflection_toplevel` documentation
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"""
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