__init__.py 文件源码

def get_col(self, alias, output_field=None):
        if output_field is None:
            output_field = self
        if alias != self.model._meta.db_table or output_field != self:
            from django.db.models.expressions import Col
            return Col(alias, self, output_field)
        else:
            return self.cached_col