How to get the latest message?

Question

Django

Hello.
It is necessary to receive and serialize the last message between users.
I am using django/django rest framework.
Model:

class Message(models.Model):
    """
    Model for user messages.
    - Who
    - Whom
    - When
    - Message
    - Status
    """
    user_sender = models.ForeignKey(User, related_name="sender")
    user_receiver = models.ForeignKey(User, related_name="receiver")
    send_date = models.DateTimeField(auto_now_add=True)
    message = models.CharField(max_length=500)
    status = models.BooleanField(default=False)

    def __unicode__(self):
        return u'%s %s ->%s' % (self.send_date, self.user_sender, self.user_receiver)

I only know the user ID.
My plan of action:
1. Get all IDs of users with whom the user has messages (for example: 1,2,3)
2. Get the last message (makes an order by date, take one value)
3. Serialize all this.
Here's what I have now:
Views

users1 = Message.objects.filter(Q(user_sender_id=token.user_id) |
                                            Q(user_receiver_id=token.user_id))\
                                    .values('user_sender_id')
            users2 = Message.objects.filter(Q(user_sender_id=token.user_id) |
                                            Q(user_receiver_id=token.user_id))\
                                    .values('user_receiver_id')
            users = User.objects.filter(Q(id__in=users1) |
                                        Q(id__in=users2))
            serializer = MessagePreviewSerializer(users, context={'user_id': token.user_id}, many=True)

Serializers

class MessagePreviewSerializer(serializers.ModelSerializer):
    info = UserProfileSerializer(many=True, read_only=True)
    last_message = serializers.SerializerMethodField('message_preview')

    def message_preview(self, obj):
        user_id = self.context.get("user_id")
        message = get_object_or_404(Message, Q(user_sender_id=user_id, user_receiver_id=obj.id) |
                                             Q(user_receiver_id=user_id, user_sender_id=obj.id))
        return message.message

    class Meta:
        model = User
        fields = ('id', 'username', 'first_name', 'last_name', 'email', 'info', 'last_message')

Naturally, this is wrong and the code does not work)
Please help me, how can I do this?

Answer 1

https://docs.djangoproject.com/en/1.8/ref/models/q...

user_send_last_msgs = Message.objects.\
   filter(user_sender=token.user_id).\
   order_by('-send_date', 'user_receiver').\
   distinct('user_receiver')
# distinct('user_receiver') postgres only

user_receive_last_msgs = Message.objects.\
   filter(user_receiver=token.user_id).\
   order_by('-send_date', 'user_sender').\
   distinct('user_sender')
for message in last_msgs:
    print message.user_sender
    print message.user_receiver
    print message.send_date
    print message.message
    print message.status