sqlalchemy.sql.schema.ForeignKey

class documentation

class ForeignKey(DialectKWArgs, SchemaItem):

Defines a dependency between two columns.

ForeignKey is specified as an argument to a _schema.Column object, e.g.:

t = Table("remote_table", metadata,
    Column("remote_id", ForeignKey("main_table.id"))
)

Note that ForeignKey is only a marker object that defines a dependency between two columns. The actual constraint is in all cases represented by the _schema.ForeignKeyConstraint object. This object will be generated automatically when a ForeignKey is associated with a _schema.Column which in turn is associated with a _schema.Table. Conversely, when _schema.ForeignKeyConstraint is applied to a _schema.Table, ForeignKey markers are automatically generated to be present on each associated _schema.Column, which are also associated with the constraint object.

Note that you cannot define a "composite" foreign key constraint, that is a constraint between a grouping of multiple parent/child columns, using ForeignKey objects. To define this grouping, the _schema.ForeignKeyConstraint object must be used, and applied to the _schema.Table. The associated ForeignKey objects are created automatically.

The ForeignKey objects associated with an individual _schema.Column object are available in the foreign_keys collection of that column.

Further examples of foreign key configuration are in :ref:`metadata_foreignkeys`.

Method	`__init__`	Construct a column-level FOREIGN KEY.
Method	`__repr__`	Undocumented
Method	`_copy`	Produce a copy of this `_schema.ForeignKey` object.
Method	`_get_colspec`	Return a string based 'column specification' for this `_schema.ForeignKey`.
Method	`_link_to_col_by_colstring`	Undocumented
Method	`_remove_from_metadata`	Undocumented
Method	`_resolve_col_tokens`	Undocumented
Method	`_set_parent`	Associate with this SchemaEvent's parent object.
Method	`_set_remote_table`	Undocumented
Method	`_set_table`	Undocumented
Method	`_set_target_column`	Undocumented
Method	`_table_key`	Undocumented
Method	`copy`	Undocumented
Method	`get_referent`	Return the `_schema.Column` in the given `_schema.Table` referenced by this `_schema.ForeignKey`.
Method	`references`	Return True if the given `_schema.Table` is referenced by this `_schema.ForeignKey`.
Class Variable	`__visit_name__`	Undocumented
Class Variable	`target_fullname`	Undocumented
Instance Variable	`_colspec`	Undocumented
Instance Variable	`_table_column`	Undocumented
Instance Variable	`_unvalidated_dialect_kw`	Undocumented
Instance Variable	`constraint`	Undocumented
Instance Variable	`deferrable`	Undocumented
Instance Variable	`info`	Info dictionary associated with the object, allowing user-defined data to be associated with this `.SchemaItem`.
Instance Variable	`initially`	Undocumented
Instance Variable	`link_to_name`	Undocumented
Instance Variable	`match`	Undocumented
Instance Variable	`name`	Undocumented
Instance Variable	`ondelete`	Undocumented
Instance Variable	`onupdate`	Undocumented
Instance Variable	`parent`	Undocumented
Instance Variable	`use_alter`	Undocumented
Property	`_column_tokens`	parse a string-based _colspec into its component parts.
Property	`_referred_schema`	Undocumented
Property	`column`	Return the target `_schema.Column` referenced by this `_schema.ForeignKey`.

Inherited from DialectKWArgs:

Class Method	`argument_for`	Add a new kind of dialect-specific keyword argument for this class.
Method	`_kw_reg_for_dialect_cls`	Undocumented
Method	`_validate_dialect_kwargs`	Undocumented
Class Variable	`_dialect_kwargs_traverse_internals`	Undocumented
Class Variable	`_kw_registry`	Undocumented
Property	`dialect_kwargs`	A collection of keyword arguments specified as dialect-specific options to this construct.
Property	`dialect_options`	A collection of keyword arguments specified as dialect-specific options to this construct.
Property	`kwargs`	A synonym for `.DialectKWArgs.dialect_kwargs`.

Inherited from SchemaItem:

Method	`_init_items`	Initialize the list of child items for this SchemaItem.
Method	`_schema_item_copy`	Undocumented
Class Variable	`_use_schema_map`	Undocumented
Class Variable	`create_drop_stringify_dialect`	Undocumented

Inherited from SchemaEventTarget (via SchemaItem):

Method _set_parent_with_dispatch Undocumented

Inherited from Traversible (via SchemaItem):

Method	`get_children`	Return immediate child `.visitors.Traversible` elements of this `.visitors.Traversible`.
Method	`__class_getitem__`	Undocumented

def __init__(self, column, _constraint=None, use_alter=False, name=None, onupdate=None, ondelete=None, deferrable=None, initially=None, link_to_name=False, match=None, info=None, **dialect_kw):

Construct a column-level FOREIGN KEY.

The _schema.ForeignKey object when constructed generates a _schema.ForeignKeyConstraint which is associated with the parent _schema.Table object's collection of constraints.

Parameters
column	A single target column for the key relationship. A `_schema.Column` object or a column name as a string: `tablename.columnkey` or `schema.tablename.columnkey`. `columnkey` is the `key` which has been assigned to the column (defaults to the column name itself), unless `link_to_name` is `True` in which case the rendered name of the column is used.
_constraint	Undocumented
use_alter	passed to the underlying `_schema.ForeignKeyConstraint` to indicate the constraint should be generated/dropped externally from the CREATE TABLE/ DROP TABLE statement. See :paramref:`_schema.ForeignKeyConstraint.use_alter` for further description. See Also :paramref:`_schema.ForeignKeyConstraint.use_alter` :ref:`use_alter`
name	Optional string. An in-database name for the key if `constraint` is not provided.
onupdate	Optional string. If set, emit ON UPDATE <value> when issuing DDL for this constraint. Typical values include CASCADE, DELETE and RESTRICT.
ondelete	Optional string. If set, emit ON DELETE <value> when issuing DDL for this constraint. Typical values include CASCADE, DELETE and RESTRICT.
deferrable	Optional bool. If set, emit DEFERRABLE or NOT DEFERRABLE when issuing DDL for this constraint.
initially	Optional string. If set, emit INITIALLY <value> when issuing DDL for this constraint.
link_to_name	if True, the string name given in `column` is the rendered name of the referenced column, not its locally assigned `key`.
match	Optional string. If set, emit MATCH <value> when issuing DDL for this constraint. Typical values include SIMPLE, PARTIAL and FULL.
info	Optional data dictionary which will be populated into the `.SchemaItem.info` attribute of this object. New in version 1.0.0.
**dialect_kw	Additional keyword arguments are dialect specific, and passed in the form `<dialectname>_<argname>`. The arguments are ultimately handled by a corresponding `_schema.ForeignKeyConstraint`. See the documentation regarding an individual dialect at :ref:`dialect_toplevel` for detail on documented arguments. New in version 0.9.2.

def __repr__(self):

overrides sqlalchemy.sql.schema.SchemaItem.__repr__

Undocumented

def _copy(self, schema=None, **kw):

Produce a copy of this _schema.ForeignKey object.

The new _schema.ForeignKey will not be bound to any _schema.Column.

This method is usually used by the internal copy procedures of _schema.Column, _schema.Table, and _schema.MetaData.

Parameters
schema	The returned `_schema.ForeignKey` will reference the original table and column name, qualified by the given string schema name.
**kw	Undocumented

def _get_colspec(self, schema=None, table_name=None):

Return a string based 'column specification' for this _schema.ForeignKey.

This is usually the equivalent of the string-based "tablename.colname" argument first passed to the object's constructor.

def _link_to_col_by_colstring(self, parenttable, table, colname):

Undocumented

def _remove_from_metadata(self, metadata):

Undocumented

def _resolve_col_tokens(self):

Undocumented

def _set_parent(self, column, **kw):

overrides sqlalchemy.sql.base.SchemaEventTarget._set_parent

Associate with this SchemaEvent's parent object.

def _set_remote_table(self, table):

Undocumented

def _set_table(self, column, table):

Undocumented

def _set_target_column(self, column):

Undocumented

def _table_key(self):

Undocumented

@util.deprecated('1.4', 'The :meth:`_schema.ForeignKey.copy` method is deprecated and will be removed in a future release.')
def copy(self, schema=None, **kw):

Undocumented

def get_referent(self, table):

Return the _schema.Column in the given _schema.Table referenced by this _schema.ForeignKey.

Returns None if this _schema.ForeignKey does not reference the given _schema.Table.

def references(self, table):

Return True if the given _schema.Table is referenced by this _schema.ForeignKey.

__visit_name__: str =

overrides sqlalchemy.sql.schema.SchemaItem.__visit_name__

Undocumented

target_fullname =

Undocumented

_colspec =

Undocumented

_table_column =

Undocumented

_unvalidated_dialect_kw =

Undocumented

constraint =

Undocumented

deferrable =

Undocumented

info =

overrides sqlalchemy.sql.schema.SchemaItem.info

Info dictionary associated with the object, allowing user-defined data to be associated with this .SchemaItem.

The dictionary is automatically generated when first accessed. It can also be specified in the constructor of some objects, such as _schema.Table and _schema.Column.

initially =

Undocumented

link_to_name =

Undocumented

match =

Undocumented

name =

Undocumented

ondelete =

Undocumented

onupdate =

Undocumented

parent =

Undocumented

use_alter =

Undocumented

@util.memoized_property
_column_tokens =

parse a string-based _colspec into its component parts.

@property
_referred_schema =

Undocumented

@util.memoized_property
column =

Return the target _schema.Column referenced by this _schema.ForeignKey.

If no target column has been established, an exception is raised.

Changed in version 0.9.0: Foreign key target column resolution now occurs as soon as both the ForeignKey object and the remote Column to which it refers are both associated with the same MetaData object.