Django - Retrieve nested fields multiple levels deep using foreign keys

Question

I'm struggling to write a Django GET that returns the following looking response:

{
"lists": [
    {
        "id": "123",
        "list_order": [
            {
                "id": "123_1",
                "order": 1,
                "list_id": "123",
                "item_id": 9876,
                "item": {
                   "id": 9876,
                   "name": "item1",
                   "location": "California"
                }
            },
            {
                "id": "123_2",
                "order": 2,
                "list_id": "123",
                "item_id": 2484,
                "item": {
                   "id": 2484,
                   "name": "item2",
                   "location": "California"
                }
            }            
        ],
        "updated_date": "2018-03-15T00:00:00Z"
    }
  ]
}

Given a list_id, the response returns the basic information on the list ("id", "updated_date"), as well as the order of items in the list. Inside each item in the list order, it also grabs the related item details (nested in "item"). I'm able to get this response without the "item" details ("id", "name", "location" fields) and with no error:

{
"lists": [
    {
        "id": "123",
        "list_order": [
            {
                "id": "123_1",
                "order": 1,
                "list_id": "123",
                "item_id": 9876
            },
            {
                "id": "123_2",
                "order": 2,
                "list_id": "123",
                "item_id": 2484
            }            
        ],
        "updated_date": "2018-03-15T00:00:00Z"
    }
  ]
}

Again there is no error, and I can retrieve the first nested level without any issue. The problem is getting the "item" information to show within each "list_order". Below are my models, serializers, and views.

models.py

class Lists(models.Model):
    id = models.CharField(null=False, primary_key=True, max_length=900)
    updated_date = models.DateTimeField(blank=True, null=True)

    class Meta:
        managed = False
        db_table = 'tbl_lists'

class Items(models.Model):
    id = models.BigIntegerField(primary_key=True)
    name = models.TextField(blank=True, null=True)
    location = models.TextField(blank=True, null=True)

    class Meta:
        managed = False
        db_table = 'tbl_items'

class ListOrder(models.Model):
    id = models.CharField(null=False, primary_key=True, max_length=900)
    list_id = models.ForeignKey(Lists, db_column='list_id', related_name='list_order')
    item_id = models.ForeignKey(Items, db_column='item_id', related_name='items')
    order = models.BigIntegerField(blank=True, null=True)

    class Meta:
        managed = False
        db_table = 'tbl_list_order'

serializers.py

class ItemsSerializer(serializers.ModelSerializer):

    class Meta:
        model = Items
        fields = '__all__'

class ListOrderSerializer(serializers.ModelSerializer):

    item = ItemsSerializer(many=False, read_only=True)

    class Meta:
        model = ListOrder
        fields = '__all__'

class ListsSerializer(serializers.ModelSerializer):

    list_order = ListOrderSerializer(many=True, read_only=True)

    class Meta:
        model = Lists
        fields = '__all__'

views.py

class ListsViewSet(generics.ListCreateAPIView):
    """
      API endpoint that returns a list with its meta-information
    """

    queryset = Lists.objects.all()
    serializer_class = ListsSerializer  

    def get_queryset(self):
        list_id = self.kwargs['list_id']

        filters = [Q(id=list_id)]

        return Lists.objects.filter(*filters)


    def list(self, request, list_id):

        queryset = self.get_queryset()

        list_serializer = ListsSerializer(queryset, many=True)

        return Response({ 'lists': list_serializer.data })

I'm pretty new to Django and like what it offers so far, though maybe I'm thinking of doing this in too much of a "SQL" way. I've read about select_related() and prefetch_related(), but not sure how I would apply it to this case. Any assistance is greatly appreciated and let me know if there's any other information I can provide.

Peter Sobhi · Accepted Answer · 2018-05-28 03:47:50Z

2

In your ListOrderSerializer you are trying to serialize item. while in ListOrder model you used the field name item_id

Solution:

In ListOrderSerializer:

class ListOrderSerializer(serializers.ModelSerializer):
    item_id = ItemsSerializer(many=False, read_only=True)
    ...

answered May 28, 2018 at 3:47

Peter Sobhi

2,5502 gold badges24 silver badges28 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Django - Retrieve nested fields multiple levels deep using foreign keys

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related