Class ExpressionWrapper

django/db/models/expressions.py:1548–1581

An expression that can wrap another expression so that it can provide extra context to the inner expression, such as the output_field.

@deconstructible(path="django.db.models.ExpressionWrapper")
class ExpressionWrapper(SQLiteNumericMixin, Expression):
    """
    An expression that can wrap another expression so that it can provide
    extra context to the inner expression, such as the output_field.
    """

    def __init__(self, expression, output_field):
        super().__init__(output_field=output_field)
        self.expression = expression

    def set_source_expressions(self, exprs):
        self.expression = exprs[0]

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

    def get_group_by_cols(self):
        if isinstance(self.expression, Expression):
            expression = self.expression.copy()
            expression.output_field = self.output_field
            return expression.get_group_by_cols()
        # For non-expressions e.g. an SQL WHERE clause, the entire
        # `expression` must be included in the GROUP BY clause.
        return super().get_group_by_cols()

    def as_sql(self, compiler, connection):
        return compiler.compile(self.expression)

    def __repr__(self):
        return "{}({})".format(self.__class__.__name__, self.expression)

    @property
    def allowed_default(self):
        return self.expression.allowed_default


class NegatedExpression(ExpressionWrapper):