Class Computed

lib/sqlalchemy/sql/schema.py:6417–6520

Defines a generated column, i.e. "GENERATED ALWAYS AS" syntax. The :class:`.Computed` construct is an inline construct added to the argument list of a :class:`_schema.Column` object:: from sqlalchemy import Computed Table( "square", metadata_obj,

class Computed(FetchedValue, SchemaItem):
    """Defines a generated column, i.e. "GENERATED ALWAYS AS" syntax.

    The :class:`.Computed` construct is an inline construct added to the
    argument list of a :class:`_schema.Column` object::

        from sqlalchemy import Computed

        Table(
            "square",
            metadata_obj,
            Column("side", Float, nullable=False),
            Column("area", Float, Computed("side * side")),
        )

    See the linked documentation below for complete details.

    .. seealso::

        :ref:`computed_ddl`

    """

    __visit_name__ = "computed_column"

    column: Optional[Column[Any]]

    @_document_text_coercion(
        "sqltext", ":class:`.Computed`", ":paramref:`.Computed.sqltext`"
    )
    def __init__(
        self, sqltext: _DDLColumnArgument, persisted: Optional[bool] = None
    ) -> None:
        """Construct a GENERATED ALWAYS AS DDL construct to accompany a
        :class:`_schema.Column`.

        :param sqltext:
          A string containing the column generation expression, which will be
          used verbatim, or a SQL expression construct, such as a
          :func:`_expression.text`
          object.   If given as a string, the object is converted to a
          :func:`_expression.text` object.

        :param persisted:
          Optional, controls how this column should be persisted by the
          database.   Possible values are:

          * ``None``, the default, it will use the default persistence
            defined by the database.
          * ``True``, will render ``GENERATED ALWAYS AS ... STORED``, or the
            equivalent for the target database if supported.
          * ``False``, will render ``GENERATED ALWAYS AS ... VIRTUAL``, or
            the equivalent for the target database if supported.

          Specifying ``True`` or ``False`` may raise an error when the DDL
          is emitted to the target database if the database does not support
          that persistence option.   Leaving this parameter at its default
          of ``None`` is guaranteed to succeed for all databases that support