Subquerying in Django - mysql

Question

I have a Django 1.9 project implementing small chat app. All messages from a certain recipient are grouped into dialogs, so the models are defined as follows:
class Dialog(models.Model):
# Some fields
class Message(models.Model):
dialog = models.ForeignKey(Dialog, ...)
text = models.TextField()
is_read = models.BooleanField(default = False)
My goal is to render a template with a table that renders dialogs. And for each dialog in the table, I need to see
the number of unread messages and
the text of the last message.
To illustrate, consider mock-data below:
Input:
id dialog_id message is_read
1 1 Hello, sir false
2 1 My name is true
3 1 Jack true
4 2 This site false
5 2 is perfect false
6 2 Cheers false
Desired output:
dialog_id last_message_in_dialog unread_messages_count
1 Jack 1
2 Cheers 3
In pure mysql, I would write a query like this:
select
a.dialog_id,
text as last_message_in_dialog,
(select count(*) from message
where dialog_id = a.dialog_id and is_read = false) as unread_messages_count
from message a
where id in (select max(id) from message group by dialog_id)
In Django terms, I have the code below:
max_id_qs = Message.objects.\
values('dialog__id').\
annotate(max_id = Max('id'),).values('max_id')
qs = Message.objects.filter(id__in = max_id_qs).\
values('dialog__id', 'text')
This code serves well to fetch the last message in each dialog. However, the problem is that I can't figure out how to implement the subquery (select count(*) from message where dialog_id = a.dialog_id and is_read = false) in Django. Maybe my total approach with max_id_qsis wrong, and there's more elegant and clear way to implement the query in Django ORM?
I've spent an entire day trying to solve this issue. help me please !

Answer 1

This will work :-
allDistinctIdWithNotReadMsg =
Message.objects.filter(is_read=False).values('id').annotate(the_count=Count('is_read',distinct('id')))
for ids in allDistinctIdWithNotReadMsg:
lastMsg = Message.objects.filter(dialog_id=ids['id']).order_by("-id")[0]
for msg in lastMsg:
print ids['id'] ,msg.message,ids['the_count']