ModelAdmin.get_queryset doesn't accept ValueQuerySet

[Piotr Roszatycki]

Django Admin crashes for following code:

models.py

from django.db import models
from django.contrib.auth.models import User


class Category(models.Model):
    name = models.CharField(max_length=100)

    class Meta:
        verbose_name_plural = 'categories'

    def __unicode__(self):
        return self.name


class Note(models.Model):
    user = models.ForeignKey(User)
    category = models.ForeignKey(Category)
    keywords = models.CharField(max_length=400)
    title = models.CharField(max_length=200)
    date = models.DateTimeField()
    content = models.TextField(max_length=50000)

    def __unicode__(self):
        return self.title


class UserNotesReport(models.Model):
    user = models.CharField(max_length=30, primary_key=True)
    category = models.CharField(max_length=100, primary_key=True)
    n = models.IntegerField()

admin.py

from django.contrib import admin

import hello_blog.models as models

from django.db.models import Count


class CategoryAdmin(admin.ModelAdmin):
    pass

admin.site.register(models.Category, CategoryAdmin)


class NoteAdmin(admin.ModelAdmin):
    pass

admin.site.register(models.Note, NoteAdmin)


class UserNotesReportAdmin(admin.ModelAdmin):
    actions = None
    list_display = ['user__username', 'category__name', 'n']
    list_display_links = None
    readonly_fields = ['user', 'category', 'n']

    def user__username(self):
        pass

    def category__name(self):
        pass

    def get_queryset(self, request):
        qs = models.Note.objects.order_by('user', 'category').values('user__username', 'category__name').annotate(n=Count('*'))
        print(qs.query)
        return qs

    def has_add_permission(self, request):
        return False

admin.site.register(models.UserNotesReport, UserNotesReportAdmin)

The fix is trivial:

diff --git a/django/contrib/admin/templatetags/admin_list.py b/django/contrib/admin/templatetags/admin_list.py
index f4033e2..9e70f8c 100644
--- a/django/contrib/admin/templatetags/admin_list.py
+++ b/django/contrib/admin/templatetags/admin_list.py
@@ -199,7 +199,10 @@ def items_for_result(cl, result, form):
         empty_value_display = cl.model_admin.get_empty_value_display()
         row_classes = ['field-%s' % field_name]
         try:
-            f, attr, value = lookup_field(field_name, result, cl.model_admin)
+            if isinstance(result, dict):
+                f, attr, value = None, field_name, result.get(field_name)
+            else:
+                f, attr, value = lookup_field(field_name, result, cl.model_admin)
         except ObjectDoesNotExist:
             result_repr = empty_value_display
         else:

[Simon Charette]

This looks like a duplicate of #24387 to me.

From what I understand you are adding this explicit values() call to GROUP BY related username and category?

[Piotr Roszatycki]

Oh, it is probably the duplicate of this bug.

Yes, this is for GROUP BY statement and not only for related model (it might be a simple field, too).

Django Admin view might not be the best option for showing aggregated queryset, but as far as the fix is very simple, I think it might be supported. And other options are still worse: creating view in raw SQL, using dedicated view (with pagination, filters, actions, oh my... it would be a huge rewrite of admin stuff).

[Piotr Roszatycki]

I tried to override Admin's internals so it is possible to use it with official Django 1.8.4 (with or without Django Suit template). The result is ​https://gist.github.com/dex4er/c658c38c3a12df7b92fc

As you can see there is a lot of duplicated code: 2 meaning lines of code and 153 lines of copy-and-paste :(

[Simon Charette]

I understand your use case but I'm not sure simply allowing get_queryset() to return a ValueQuerySet will do here.

From what I understand this will break many things since your results omit the pk from the results. Your provided examples are good example of customization required to make this work (e.g list_display mapping to methods, has_add_permission returning False) and silence strange errors the admin code might be raising.

I'm still not convinced we should accept this new feature, even with a defined use case.

[Tim Graham]

Yes, I think when you find yourself overriding large portions of the admin, it's time to write your own views.

[Piotr Roszatycki]

Writing own view which supports paging, filtering, actions, ordering and import/export (via additional packages) means that I need to copy-and-paste large portions of the admin view or need to reinvent the wheel.

I think adding a few methods and settings to ModelAdmin is still better option.

This patch doesn't break anything else in Django and just allows to make some new use cases for admin interface...

[Tim Graham]

I believe a different API to construct the desired query might be the proper solution.

[Piotr Roszatycki]

I'm not sure what do you mean "different API".

I've refactored this example use case and created "database view" with model.Manager. The fields are aliased with annotate(aliased_field=F('original_field')).

This solution works also with django-import-export, so I can generate CSV or XLS file based on this aggregated QuerySet!

models.py

from django.db import models
from django.db.models import Count, F
from django.contrib.auth.models import User


class Category(models.Model):
    name = models.CharField(max_length=100)

    class Meta:
        verbose_name_plural = 'categories'


class Note(models.Model):
    user = models.ForeignKey(User)
    category = models.ForeignKey(Category)
    keywords = models.CharField(max_length=400)
    title = models.CharField(max_length=200)
    date = models.DateTimeField()
    content = models.TextField(max_length=50000)


class UserNotesReportManager(models.Manager):
    def get_queryset(self):
        return Note.objects \
            .annotate(user_username=F('user__username'),
                      category_name=F('category__name')) \
            .values('user_username', 'category_name') \
            .order_by('user_username', 'category_name') \
            .annotate(n=Count('*'))


class UserNotesReport(models.Model):
    user_username = models.CharField(max_length=30, primary_key=True)
    category_name = models.CharField(max_length=100, primary_key=True)
    n = models.IntegerField()

    objects = UserNotesReportManager()

admin.py

from django.contrib import admin

import hello_blog.models as models


class CategoryAdmin(admin.ModelAdmin):
    pass

admin.site.register(models.Category, CategoryAdmin)


class NoteAdmin(admin.ModelAdmin):
    pass

admin.site.register(models.Note, NoteAdmin)


class UserNotesReportAdmin(admin.ModelAdmin):
    actions = None
    list_display = ['user_username', 'category_name', 'n']
    list_display_links = None
    readonly_fields = list_display

    def has_add_permission(self, request):
        return False

admin.site.register(models.UserNotesReport, UserNotesReportAdmin)

This example is available at ​https://github.com/dex4er/django-hello-world/tree/blog_reports so you can check if the modification works correctly.

[Tim Graham]

I mean a different way to construct the GROUP BY query without using values().