Pass a custom queryset to serializer in Django Rest Framework

Question

I am using Django rest framework 2.3 I have a class like this

class Quiz():
    fields..

# A custom manager for result objects
class SavedOnceManager(models.Manager):                                                                                                                                                                                                
    def filter(self, *args, **kwargs):
        if not 'saved_once' in kwargs:
            kwargs['saved_once'] = True
        return super(SavedOnceManager, self).filter(*args, **kwargs)

class Result():
    saved_once = models.NullBooleanField(default=False, db_index=True,
                                         null=True)
    quiz = models.ForeignKey(Quiz, related_name='result_set')

    objects = SavedOnceManager()

As you see I have a custom manager on results so Result.objects.filter() will only return results that have save_once set to True

Now my Serializers look like this:

class ResultSerializer(serializers.ModelSerializer):                                                                                                                                                                                                    
      fields...

class QuizSerializer(serializers.ModelSerializer):                                                                                                                                                                                                      
    results = ResultSerializer(many=True, required=False, source='result_set')

Now if I serializer my quiz it would return only results that have saved_once set to True. But for a particular use case I want the serializer to return all objects. I have read that I can do that by passing a queryset parameter http://www.django-rest-framework.org/api-guide/relations/ in (further notes section). However when I try this

results = ResultSerializer(many=True, required=False, source='result_set',
                           queryset=
                               Result.objects.filter(
                               saved_once__in=[True, False]))

I get TypeError: __init__() got an unexpected keyword argument 'queryset' And looking at the source code of DRF(in my version atleast) it does not accept a queryset argument.

Looking for some guidance on this to see if this is possible... thanks!

This is confusing. 'result_set' of the QuizSerializer should still contain all results as filter() is not being called on the related object. Can you add the query from your view code? — Mark Galloway

Mark Galloway Mark Galloway · Accepted Answer · 2015-07-09T09:23:07

In my opinion, modifying filter like this is not a very good practice. It is very difficult to write a solution for you when I cannot use filter on the Result model without this extra filtering happening. I would suggest not modifying filter in this manner and instead creating a custom manager method which allows you to apply your filter in an obvious way where it is needed, eg/

class SavedOnceManager(models.Manager):                                                                                                                                                                                                
    def saved_once(self):
        return self.get_queryset().filter('saved_once'=True)

Therefore, you can query either the saved_once rows or the unfiltered rows as you would expect:

Results.objects.all()
Results.objects.saved_once().all()

Here is one way which you can use an additional queryset inside a serializer. However, it looks to me that this most likely will not work for you if the default manager is somehow filtering out the saved_once objects. Hence, your problem lies elsewhere.

class QuizSerializer(serializers.ModelSerializer):  
    results = serializers.SerializerMethodField()

    def get_results(self, obj):
        results = Result.objects.filter(id__in=obj.result_set)
        return ResultSerializer(results, many=True).data

Pass a custom queryset to serializer in Django Rest Framework

1 Answers