Python django.db.models.expressions 模块，Func() 实例源码

def as_oracle(self, compiler, connection):
        # we can't mix TextField (NCLOB) and CharField (NVARCHAR), so convert
        # all fields to NCLOB when we expect NCLOB
        if self.output_field.get_internal_type() == 'TextField':
            class ToNCLOB(Func):
                function = 'TO_NCLOB'

            expressions = [
                ToNCLOB(expression) for expression in self.get_source_expressions()]
            self.set_source_expressions(expressions)
        return super(Coalesce, self).as_sql(compiler, connection)