Django ORM: Group by and Max

django django-orm
jeffreyveon picture jeffreyveon · Aug 4, 2011 · Viewed 12.7k times · Source

I have a model that looks like this:

Requests: user, req_time, req_text

In the DB, the records can look like this:

id, user_id, req_time, req_text
1     1      TIMESTAMP  YES
2     1      TIMESTAMP  NO
3     2      TIMESTAMP  YES

etc.

How do I write a Django ORM query that: groups the Requests by user, filters the Requests based on req_text, and also, select the max id of the resulting result set. So for each user, I will return one row which matches the filter condition and also has the greatest id.

Answer

Botond Béres picture Botond Béres · Aug 4, 2011 
from django.db.models.aggregates import Max

request_values = Requests.objects.filter(req_text='YES') \
                 .values('user') \
                 .annotate(max_id=Max('id'))

Then request_values will look like this:

[
    {'user': 1, 'max_id': 1},
    {'user': 2, 'max_id': 4},
    {'user': 3, 'max_id': 5},
    {'user': 4, 'max_id': 12},
    ...
]

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