Class DefaultClause

lib/sqlalchemy/sql/schema.py:4415–4465

A DDL-specified DEFAULT column value. :class:`.DefaultClause` is a :class:`.FetchedValue` that also generates a "DEFAULT" clause when "CREATE TABLE" is emitted. :class:`.DefaultClause` is generated automatically whenever the ``server_default``, ``server_onupdate`` arguments of

class DefaultClause(FetchedValue):
    """A DDL-specified DEFAULT column value.

    :class:`.DefaultClause` is a :class:`.FetchedValue`
    that also generates a "DEFAULT" clause when
    "CREATE TABLE" is emitted.

    :class:`.DefaultClause` is generated automatically
    whenever the ``server_default``, ``server_onupdate`` arguments of
    :class:`_schema.Column` are used.  A :class:`.DefaultClause`
    can be passed positionally as well.

    For example, the following::

        Column("foo", Integer, server_default="50")

    Is equivalent to::

        Column("foo", Integer, DefaultClause("50"))

    """

    has_argument = True

    def __init__(
        self,
        arg: Union[str, ClauseElement, TextClause],
        for_update: bool = False,
        _reflected: bool = False,
    ) -> None:
        util.assert_arg_type(arg, (str, ClauseElement, TextClause), "arg")
        super().__init__(for_update)
        self.arg = arg
        self.reflected = _reflected

    @util.memoized_property
    @util.preload_module("sqlalchemy.sql.functions")
    def _is_monotonic_fn(self) -> bool:
        functions = util.preloaded.sql_functions
        return (
            isinstance(self.arg, functions.FunctionElement)
            and self.arg.monotonic
        )

    def _copy(self) -> DefaultClause:
        return DefaultClause(
            arg=self.arg, for_update=self.for_update, _reflected=self.reflected
        )

    def __repr__(self) -> str:
        return "DefaultClause(%r, for_update=%r)" % (self.arg, self.for_update)


class Constraint(DialectKWArgs, HasConditionalDDL, SchemaItem):