如何在Python中设置一个空消息的ProtoBuf字段？

Question

以下是Google Protocol Buffer（.proto）文件的内容

message First
{
    required uint32 field1 = 1;

    optional MessageType1 request = 2;
}

message MessageType1
{
}

我想设置MessageType1字段请求。 但我认为这是一个错误：

AttributeError: Assignment not allowed to composite field "request" in protocol message object.

如何在Python中设置此空消息的值？

Answer 1

在Proto Buffer的Message类的源代码中得到了这个。

  def SetInParent(self):
    """Mark this as present in the parent.

    This normally happens automatically when you assign a field of a
    sub-message, but sometimes you want to make the sub-message
    present while keeping it empty.  If you find yourself using this,
    you may want to reconsider your design."""

所以设置这样一个空消息的方法是调用这个函数：

first.request.SetInParent()