Django Nested Relation API response

Question

I have two models District and BTS. I want to get the response like bellow.

[{
    "id": 15,
    "name": "Westen",
    "page": 1,
    "expanded": false,
    "selected": false,
    "children": [{
        "id": 12,
        "name": "BTS2",
        "page": 1
    }]
}, {
    "id": 13,
    "name": "Noth",
    "page": 1,
    "children": [{
        "id": 13,
        "name": "BTS2",
        "page": 2
    }]
}]

I have two Serializer

class BTSSerializer(serializers.HyperlinkedModelSerializer):

    def to_representation(self, value):
        return {
            'id': value.id,
            'name': value.bts_id,
            "page": 4,
            "expanded": False,
            "selected": False,
        }

    class Meta:
        model = BTS
        fields = ('bts_id', 'id')


class DistrictSerializer(serializers.HyperlinkedModelSerializer):

    def to_representation(self, value):
        return {
            'id': value.id,
            'name': value.name,
            "page": 1,
            "expanded": False,
            "selected": False,
            "children": []
        }

    class Meta:
        model = District
        fields = ('name', 'id')

This is BTS model

class BTS(models.Model):

    id = models.AutoField(primary_key=True)
    bts_id = models.CharField(max_length = 100, unique=True)
    district_id = models.ForeignKey(District, related_name='districts', on_delete=models.CASCADE, null=True)
    bts_type_id = models.ForeignKey(BTSType, related_name='types', on_delete=models.CASCADE, null=True)

    class Meta:
        db_table = "base_stations"

    def __str__(self):
        return self.bts_id

I changed as follows

class DistrictSerializer(serializers.HyperlinkedModelSerializer):

    bts = BTSSerializer(many=True)

    def to_representation(self, value):
        return {
            'id': value.id,
            'name': value.name,
            "page": 1,
            "expanded": False,
            "selected": False,
            "children": value.bts
        }

    class Meta:
        model = District
        fields = ('name', 'id', 'bts')

How could I achieve this ?

Got this error

AttributeError at /tree_parents/

'District' object has no attribute 'bts'

Request Method:     GET
Request URL:    http://localhost:8000/tree_parents/
Django Version:     2.2
Exception Type:     AttributeError
Exception Value:    

'District' object has no attribute 'bts'

Exception Location:     /home/samitha/workspace/techlead/tas-test/api/serializers.py in to_representation, line 45

i already followed that. when i add bts to field list it says bts is not in District — underscore
– underscore, Commented Apr 25, 2019 at 6:17
show the full Traceback, but if that is the case then error is self-explanatory, add bts to district, check the drf example again — copser
– copser, Commented Apr 25, 2019 at 6:24

score 2 · Accepted Answer · 2019-04-25 07:48:30Z

2

better to see your District model, but you can try the solution:

class DistrictSerializer(serializers.HyperlinkedModelSerializer):

    children = BTSSerializer(source='districts', many=True)
    num_children = serializers.SerializerMethodField()
    page = serializers.SerializerMethodField()
    expanded = serializers.SerializerMethodField()
    selected = serializers.SerializerMethodField()

    def get_page(self, obj):
        return 1
    def get_expanded(self, obj):
        return False
    def get_selected(self, obj):
        return False
    def get_num_children(self, obj):
        return obj.districts.count()

    class Meta:
        model = District
        fields = ('name', 'id', 'children', 'page', 'expanded', 'selected')

edited Apr 25, 2019 at 7:48

answered Apr 25, 2019 at 7:02

user8060120

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6 Comments

underscore Over a year ago

what is bts_set meanning ?

underscore Over a year ago

Got AttributeError when attempting to get a value for field children on serializer DistrictSerializer. The serializer field might be named incorrectly and not match any attribute or key on the District instance. Original exception text was: 'District' object has no attribute 'bts_set'. Request Method:

user8060120 Over a year ago

i hope a fixed, _set is default name for related objects docs.djangoproject.com/en/2.2/ref/models/relations/…, but you set the related_name so should be districts. Better to change it to the bts.

underscore Over a year ago

i works well. i want to get the children count to the parent object. how could i get it ?

user8060120 Over a year ago

create model property or serialized method

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