How to use custom manager with related objects?

Question

I have a custom manager. I want to use it for related objects. I found use_for_related_fields in docs. But it does not work the way I used it:

class RandomQueryset(models.query.QuerySet):      def randomize(self):                count = self.count()         random_index = random.randint(0, count - 1)         return self.all()[random_index]   class RandomManager(models.Manager):      use_for_related_fields = True      def get_query_set(self):         return RandomQueryset(self.model, using=self._db)      def randomize(self):         return self.get_query_set().randomize() 

I used it for one model:

>>> post = PostPages.default_manager.filter(image_gallery__isnull=False).distinct().randomize() 

And tried to do the same with m2m related object:

>>> post.image_gallery.randomize() 

Got an error:

AttributeError: 'ManyRelatedManager' object has no attribute 'randomize' 

Is it possible to use a custom manager in the way I did it? If so, how do you make it work?

Edit

My models:

class ShivaImage(models.Model, ImageResizing):     image = models.ImageField(upload_to='img')     slide_show = models.BooleanField()      title = models.CharField(max_length=100)     text = models.TextField(max_length=400)     ordering = models.IntegerField(blank=True, null=True)      objects = RandomManager()   class PostPages(models.Model):     image_gallery = models.ManyToManyField(ShivaImage, blank=True,                                        related_name='gallery',)     # all the other fields...       objects = RandomManager() 

Answer 1

For completeness of the topic, Django 1.7 (finally) supports using a custom reverse manager, so you can do something like that (just copying from the django docs):

from django.db import models  class Entry(models.Model):     objects = models.Manager()  # Default Manager     entries = EntryManager()    # Custom Manager  b = Blog.objects.get(id=1) b.entry_set(manager='entries').all()