Support filtering by non-database (queryset) fields in the admin

[Samuel Cormier-Iijima]

It's currently impossible to filter the admin interface by non-database fields, even if the fields are being selected in the queryset.

The attached patch lets you do something like this:

class Author(models.Model):
	name = models.CharField(max_length=255)

class Book(models.Model):
	author = models.ForeignKey(Author)

class AuthorAdmin(admin.ModelAdmin):
	list_display = ['name', 'books']
	list_filter = [models.IntegerField(verbose_name='number of books', name='num_books')]

	def books(self, obj):
		return obj.num_books
	books.short_description = 'Number of books'

	def queryset(self, request):
		return super(AuthorAdmin, self).queryset(request).annotate(num_books=models.Count('book'))

admin.site.register(Author, AuthorAdmin)
admin.site.register(Book)

which would show all of the values for num_books in the available filters. (This particular example only works in MySQL, but could be applied to fields selected with .extra(select=...) instead of .annotate).

[kris_b]

I totally support your idea, sciyoshi, I just stumbled upon this myself - I added annotation to the queryset method and actually was surprised by the ImproperyConfigured exception. A big request to Django decision makers: please add support for this feature!

By the way, as I am new to the community: Great work, guys! Keep it up!

[Russell Keith-Magee]

I'll accept the idea of being able to filter on annotated fields, but I don't particularly like the implementation you provide. It strikes me as a whole lot more complex than it should be from an end-users point of view.

Patch also requires tests and documentation.

[Yeago]

Forgive me if I'm being presumptuous but it seems like #5833 would encompass this. Closing as dupe.