Fetching nested objects with Django REST framework

Question

I am attempting to fetch nested objects but not quite sure how to achieve this. My model is as shown:

class Brand(models.Model)
    name = models.CharField(max_length=128)

class Size(models.Model)
    name = models.CharField(max_length=128)

class Brand_Size(models.Model)
    brand = models.ForeignKey(Brand)
    size = models.ForeignKey(Size)

class Brand_Size_Location(models.Model)
    location = models.ForeignKey(Location)
    brand_size = models.ForeignKey(Brand_Size)

I filter objects in Brand_Size_Location by location which can occur 1..x. I want my serializer to output the results in terms of the model Brand (BrandSerializer). Since my resultset can be 1..x and furthermore the occurrence of Brand can be duplicates i would like to eliminate these aswell at the same time.

Fiver · Accepted Answer · 2014-04-19 16:58:04Z

1

You should be able to do this fairly easily by including a serializer field in your BrandSerializer:

class BrandSerializer(serializers.ModelSerializer):
    brand_sizes = BrandSizeSerializer(
        source='brand_size_set',
        read_only=True
    )

    class Meta:
        model = Brand
        fields = (
            'id',
            ...add more fields you want here
            'brand_sizes')

You can simlarly create the brand size serializer to nest the locations

Filtering on this relationship occurs in the view and will need a custom filter. Here's a basic example using a ListView:

class BrandFilter(django_filters.FilterSet):
    location = django_filters.ModelMultipleChoiceFilter(
        queryset=Brand_Size_Location.objects.all(),
        name='brand_size__brand_size_location__location'
    )
    location_name = django_filters.CharFilter(
        name='brand_size__brand_size_location__location__name'
    )

class Meta:
    model = Brand
    fields = [
        'location',
        'location_name'
    ]

class BrandList(LoginRequiredMixin, generics.ListCreateAPIView): model = Brand serializer_class = BrandSerializer filter_class = BrandFilter

You can then use query parameters to filter on the URL like:

http://somehost/api/brands/?location=42

which uses a PK to filter, or with the location name (assuming you have a name field in the Location model):

http://somehost/api/brands/?location_name=Atlantis

edited Apr 19, 2014 at 16:58

answered Apr 19, 2014 at 16:08

Fiver

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11 Comments

JavaCake Over a year ago

So the result i get from filtering objects in Brand_Size_Location i simply serialize with BrandSerializer? Or how is this done in practice..

Fiver Over a year ago

@JavaCake Not sure if I'm following completely, but filtering isn't done in the serializer, but in the view. To filter on a nested relationship will require writing a custom filter, which is quite easy actually...I'll update my answer with an example

JavaCake Over a year ago

Im sorry for misleading you with my question. Basically what i mean is, can i take the resultset from my filtering of Brand_Size_Location and apply the serializer to it (BrandSerializer)?

Fiver Over a year ago

Ahh, so you are using Brand_Size_Location as the model for the view, and want to have a nested Brand field with it's own nested info?

JavaCake Over a year ago

Exactly. The filtering is occuring on the Brand_Size_Location model. Where i become a little confused is how to serialize it so deep. I attempted to mess around with depth but i did not exactly get what i wanted. So what i want is to take my resultset from the filtering, get all Brand_Size followed by Brand where i eliminate the duplicates. So basically i will end up with a list of Brand items.

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