问在使用这种多对多关系之前，“<Message:title>”需要有一个字段“id”的值。

EN

class Message(models.Model):
    """
    消息
    """
    message_num = models.CharField(default=getMessageNum, max_length=16, help_text="消息") # 注意：message_num 相同，说明是同一次发送

    title = models.CharField(max_length=64, help_text="消息名称")
    content = models.CharField(max_length=1024, help_text="消息内容")

    create_user = models.ForeignKey(User, related_name="created_messages",help_text="创建者")
    receive_user = models.ManyToManyField(User, related_name="received_messages", help_text="接受者")


    def __str__(self):
        return self.title
    def __unicode__(self):
        return self.title

try:
    receive_user = User.objects.get(id=user_id)
    message = Message.objects.create(
        title=title,
        content=content,
        create_user=create_user,
        receive_user=receive_user,
    )
    message.save()
except Exception as e:
    raise e

"" needs to have a value for field "id" before this many-to-many relationship can be used.