Class ForeignKeyConstraint

lib/sqlalchemy/sql/schema.py:4966–5276

A table-level FOREIGN KEY constraint. Defines a single column or composite FOREIGN KEY ... REFERENCES constraint. For a no-frills, single column foreign key, adding a :class:`_schema.ForeignKey` to the definition of a :class:`_schema.Column` is a shorthand equivalent for an unna

class ForeignKeyConstraint(ColumnCollectionConstraint):
    """A table-level FOREIGN KEY constraint.

    Defines a single column or composite FOREIGN KEY ... REFERENCES
    constraint. For a no-frills, single column foreign key, adding a
    :class:`_schema.ForeignKey` to the definition of a :class:`_schema.Column`
    is a
    shorthand equivalent for an unnamed, single column
    :class:`_schema.ForeignKeyConstraint`.

    Examples of foreign key configuration are in :ref:`metadata_foreignkeys`.

    """

    __visit_name__ = "foreign_key_constraint"

    def __init__(
        self,
        columns: _typing_Sequence[_DDLColumnArgument],
        refcolumns: _typing_Sequence[_DDLColumnReferenceArgument],
        name: _ConstraintNameArgument = None,
        onupdate: Optional[str] = None,
        ondelete: Optional[str] = None,
        deferrable: Optional[bool] = None,
        initially: Optional[str] = None,
        use_alter: bool = False,
        link_to_name: bool = False,
        match: Optional[str] = None,
        table: Optional[Table] = None,
        info: Optional[_InfoType] = None,
        comment: Optional[str] = None,
        **dialect_kw: Any,
    ) -> None:
        r"""Construct a composite-capable FOREIGN KEY.

        :param columns: A sequence of local column names. The named columns
          must be defined and present in the parent Table. The names should
          match the ``key`` given to each column (defaults to the name) unless
          ``link_to_name`` is True.

        :param refcolumns: A sequence of foreign column names or Column
          objects. The columns must all be located within the same Table.

        :param name: Optional, the in-database name of the key.

        :param onupdate: Optional string. If set, emit ON UPDATE <value> when
            issuing DDL for this constraint. Typical values include CASCADE,
            DELETE and RESTRICT.

            .. seealso::

                :ref:`on_update_on_delete`

        :param ondelete: Optional string. If set, emit ON DELETE <value> when
            issuing DDL for this constraint. Typical values include CASCADE,
            SET NULL and RESTRICT.  Some dialects may allow for additional
            syntaxes.