Getting a count of objects in a queryset in django

Question

How can I add a field for the count of objects in a database  I have the following models   class Item models Model       name   models CharField    class Contest models Model       name   models CharField    class Votes models Model       user   models ForeignKey User      item   models ForeignKey Item      contest   models ForeignKey Contest      comment   models TextField     To find the votes for contestA I am using the following query in my view  current vote   Item objects filter votes  contest contestA    This returns a queryset with all of the votes individually but I want to get the count votes for each item  anyone know how I can do that  thanks

User · Answer

Another way of doing this would be using Aggregation. You should be able to achieve a similar result using a single query. Such as this:

Item.objects.values("contest").annotate(Count("id"))

I did not test this specific query, but this should output a count of the items for each value in contests as a dictionary.

User · Answer

Use related name to count votes for a specific contest class Item models Model       name   models CharField    class Contest models Model       name   models CharField    class Votes models Model       user   models ForeignKey User      item   models ForeignKey Item      contest   models ForeignKey Contest  related name  quot contest votes quot       comment   models TextField     gt  gt  gt  comments   Contest objects get id contest id  contest votes count

User · Answer

To get the number of votes for a specific item  you would use   vote count   Item objects filter votes  contest contestA  count     If you wanted a break down of the distribution of votes in a particular contest  I would do something like the following   contest   Contest objects get pk contest id  votes     contest votes set select related    vote counts       for vote in votes    if not vote counts has key vote item id       vote counts vote item id             item   vote item         count   0          vote counts vote item id   count      1   This will create dictionary that maps items to number of votes  Not the only way to do this  but it s pretty light on database hits  so will run pretty quickly

[django] Getting a count of objects in a queryset in django

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