Class DatabaseDefault

django/db/models/expressions.py:1311–1348

Expression to use DEFAULT keyword during insert otherwise the underlying expression.

class DatabaseDefault(Expression):
    """
    Expression to use DEFAULT keyword during insert otherwise the underlying
    expression.
    """

    def __init__(self, expression, output_field=None):
        super().__init__(output_field)
        self.expression = expression

    def get_source_expressions(self):
        return [self.expression]

    def set_source_expressions(self, exprs):
        (self.expression,) = exprs

    def resolve_expression(
        self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False
    ):
        resolved_expression = self.expression.resolve_expression(
            query=query,
            allow_joins=allow_joins,
            reuse=reuse,
            summarize=summarize,
            for_save=for_save,
        )
        # Defaults used outside an INSERT context should resolve to their
        # underlying expression.
        if not for_save:
            return resolved_expression
        return DatabaseDefault(
            resolved_expression, output_field=self._output_field_or_none
        )

    def as_sql(self, compiler, connection):
        if not connection.features.supports_default_keyword_in_insert:
            return compiler.compile(self.expression)
        return "DEFAULT", ()


class Col(Expression):