expressions.py 文件源码

def as_sql(self, compiler, connection):
        try:
            lhs_output = self.lhs.output_field
        except FieldError:
            lhs_output = None
        try:
            rhs_output = self.rhs.output_field
        except FieldError:
            rhs_output = None
        if (not connection.features.has_native_duration_field and
                ((lhs_output and lhs_output.get_internal_type() == 'DurationField') or
                 (rhs_output and rhs_output.get_internal_type() == 'DurationField'))):
            return DurationExpression(self.lhs, self.connector, self.rhs).as_sql(compiler, connection)
        if (lhs_output and rhs_output and self.connector == self.SUB and
            lhs_output.get_internal_type() in {'DateField', 'DateTimeField', 'TimeField'} and
                lhs_output.get_internal_type() == rhs_output.get_internal_type()):
            return TemporalSubtraction(self.lhs, self.rhs).as_sql(compiler, connection)
        expressions = []
        expression_params = []
        sql, params = compiler.compile(self.lhs)
        expressions.append(sql)
        expression_params.extend(params)
        sql, params = compiler.compile(self.rhs)
        expressions.append(sql)
        expression_params.extend(params)
        # order of precedence
        expression_wrapper = '(%s)'
        sql = connection.ops.combine_expression(self.connector, expressions)
        return expression_wrapper % sql, expression_params