How to add a sortable count column to the Django admin of a model with a many-to-one relation?

Question

Suppose I have a Book model containing a foreign key to a Publisher model.

How can I display in the Django admin a column with the number of books published by each publisher, in a way that I can use the built-in sorting?

Answer 1

Try something like this:

class PublisherAdminWithCount(Admin):

    def book_count(self, obj):
        return obj.book_set.count()

    list_display = ('user_count',)

admin.site.register(Group, PublisherAdminWithCount)

Answer 2

Try this:

make a new Manager (and aggregate with count on the book relation field):

class PublisherManager(models.Manager):
    def get_query_set(self):
        return super(PublisherManager,self).get_query_set().annotate(pubcount=Count('book'))

sort it on pubcount:

class Publisher(models.Model):
    ......
    objects = PublisherManager()

    class Meta:
        ordering = ('pubcount',)

Answer 3

You should indeed start off with adding:

class PublisherManager(models.Manager):
    def get_query_set(self):
        return super(PublisherManager,self).get_query_set().annotate(pubcount=Count('book'))

But the correct way to add it as a sortable field is:

class Publisher(models.Model):
    ......
    objects = PublisherManager()

    def count(self):
        return self.pubcount
    count.admin_order_field = 'pubcount'

And then you can just add 'count' to the list_display attribute of model admin in admin.py