django rest framework multiple foreign keys serializing

Question

at first it looked simple, now I got confused. I wrote data structure and now struggling to get it. So far what I have:

class Area(models.Model):
    name = models.CharField(max_length=128)
    ...

class Category(models.Model):
    name = models.CharField(max_length=128)
    ....

class Venue(models.Model):
    name = models.CharField(max_length=128)
    category = models.ForeignKey(Category, related_name='venues')
    area = models.ForeignKey(Area, related_name='venues')

And I need based on Area pk get categories with venues in it. Is it possible to do so using django rest framework? The result should look something like:

  {
    "pk": 1,
    "name": "London",
    "categories": [
        {
             "pk": 1,
             "name": "Bars",
             "venues": [
                 {
                      "pk": 1,
                      "name": "Cool bar"
                 },
                 {
                      "pk": 2,
                      "name": "Cooler bar"
                 },
                 {
                      "pk": 3,
                      "name": "Coldest bar"
                 },
            ]
        }
    ]

}

Ideally I need something like this:

class VenueSerializer(serializers.ModelSerializer):
  .....

class CategorySerializer(serializers.ModelSerializer):
    venues = VenueSerializer(read_only=True, many=True)

    class Meta:
        model = Category
        fields = ('pk', 'name', 'venues', )

class AreaSerializer(serializers.ModelSerializer):
    categories = CategorySerializer(read_only=True, many=True)

    class Meta:
        model = Area
        fields = ('pk', 'name', 'categories', )

But of course this will not work since Area is not directly related to Category. So my question, is it possible to do this without changing data structure?

James Evans · Accepted Answer · 2016-08-30 18:48:42Z

2

It's a little ugly, but if you're set on the object model, you can do this using DRF's SerializerMethodField.

Your Area serializer would then look something like:

class AreaSerializer(serializers.ModelSerializer):
    categories = SerializerMethodField()

    def get_categories(self, obj):
        # this will find all categories with a venue in given area
        categories = Category.objects.filter(venues__area=obj)
        serializer = CategorySerializer(categories, many=True)
        return serializer.data

    class Meta:
        model = Area
        fields = ('pk', 'name', 'categories', )

Without optimization, this structure will generate A LOT of database queries. I'd recommend using Django's prefetch_related operation to reduce the number of redudant queries.

answered Aug 30, 2016 at 18:48

James Evans

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