我在Youtube上看了一个关于如何创建聊天应用的视频。然后它建立了一个我不理解的模型。这是我遇到的消息模型，我不理解它是如何工作的。

class Message(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE, related_name='user')
    sender = models.ForeignKey(User, on_delete=models.CASCADE, related_name='from_user')
    recipient = models.ForeignKey(User, on_delete=models.CASCADE, related_name='to_user')
    body = models.TextField()
    date = models.DateTimeField(auto_now_add=True)
    is_read = models.BooleanField(default=False)

    def send_message(from_user, to_user, body):
        sender_message = Message(user=from_user, sender=from_user, recipient=to_user, body=body, is_read=True)
        sender_message.save()

        recipient_message = Message(user=to_user, sender=from_user, recipient=from_user, body=body, is_read=True)
        recipient_message.save()

        return sender_message

    def get_message(user):
        users = []
        messages = Message.objects.filter(user=user).values('recipient').annotate(last=Max('date')).order_by('-last')
        # filter by user=the login user, recipient=the sender, the lastest message from each sender, order the lastest message by sender using time

        for message in messages:
            users.append({
                'user': User.objects.get(pk=message['recipient']),
                'last': message['last'],
                'unread': Message.objects.filter(user=user, recipient__pk=message['recipient'], is_read=False).count(),
                })

        return users

我理解Message模型的不同字段，但是我不理解为什么它在send_message()函数中创建两个消息模型示例，一个用于发送者消息，另一个用于接收者消息。

recipient_message = Message(user=to_user, sender=from_user, recipient=from_user, body=body, is_read=True)

那么对于recipient_message，我不清楚为什么recipient字段设置为from_user而不是to_user？？
有人能帮我一下吗？
我搞不清楚这个消息模型是如何工作的。