Custom Serializer and ViewSet for ManyToManyField in DRF

Question

I have a M2M relationship between the Entity and EntityGroup and I want to save the corresponding entity index to the EntityGroup just like an entity array to database.

Since I used a custom through Model with additional field index inside, I need to serialize the index to the corresponding entity to the response, how should I implement that?

I'm new to django and django-rest-framework and it seems there are not similar M2M examples after a few google search. Here is my thought, a serializer could only serialize the only one model's fields with ForeignKey relationship, a viewset could have a custom model based on queryset which could merge the relationships for a few models. So I need to implement a more expandable viewset with a custom queryset inside?

Here is my code:

models.py

class Entity(models.Model):
    uuid = models.CharField()
    name = models.CharField()

class EntityGroup(models.Model):
    name = models.CharField()
    entities = models.ManyToManyField(Entity,
        through='EntityGroupRelationship',
        through_fields=('group', 'entity'),
        related_name='groups'
    )

class EntityGroupRelationship(models.Model):
    entity = models.ForeignKey(Entity, on_delete=models.CASCADE)
    group = models.ForeignKey(EntityGroup, on_delete=models.CASCADE)
    index = models.PositiveIntegerField()

serializers.py

class EntitySerializer(serializers.ModelSerializer):
    class Meta:
        model = Entity
        fields = '__all__'

class EntityGroupRelationshipSerializer(serializers.ModelSerializer):
    class Meta:
        model = EntityGroupRelationship
        fields = '__all__'

class EntityGroupSerializer(serializers.ModelSerializer):
    entities = EntitySerializer(many=True)

    class Meta:
        model = EntityGroup
        fields = '__all__'

views.py

class EntityGroupViewSet(BaseModelViewSet):
    queryset = EntityGroup.objects.all()
    serializer_class = EntityGroupSerializer

class EntityGroupRelationshipViewSet(BaseModelViewSet):
    queryset = EntityGroupRelationship.objects.all()
    serializer_class = EntityGroupRelationshipSerializer

Current response

[
    {
        "id": 1,
        "entities": [{
            "id": 1,
            "name": "",
        }]
    },
    ...
]

Expected respponse

[
    {
        "id": 1,
        "entities": [
            {
                "index": 1,
                "info": {
                    "id": 1,
                    "name": "",
                }
            }
        ]
    },
    ...
]

score 0 · Accepted Answer · answered Aug 06 '19 at 03:56

0

You are using incorrect serializer for that. Use EntityGroupRelationshipSerializer instead of EntitySerializer. Also you need to pass correct fields

class EntitySerializer(serializers.ModelSerializer):
    class Meta:
        model = Entity
        fields = '__all__'

class EntityGroupRelationshipSerializer(serializers.ModelSerializer):
    entity = EntitySerializer()
    class Meta:
        model = EntityGroupRelationship
        fields = ('index', 'entity')

class EntityGroupSerializer(serializers.ModelSerializer):
    entities = EntityGroupRelationshipSerializer(many=True) # here should be EntityGroupRelationshipSerializer

    class Meta:
        model = EntityGroup
        fields = '__all__'

answered Aug 06 '19 at 03:56

Sardorbek Imomaliev

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Thanks Sardorbek! `EntityGroupRelationshipSerializer` is my expected one, but your `entities = EntityGroupRelationshipSerializer(many=True)` in `EntityGroupSerializer` makes me confused a lot, the `Entity` hasn't an `index` fields to serialize, (django reports that error in my a few tries,) so is that line a mistake? – Itachi Aug 06 '19 at 14:02
@Itachi didn't get your question. Could you elaborate? – Sardorbek Imomaliev Aug 06 '19 at 16:05
Forget that, problem resolved, my bad. :) – Itachi Aug 07 '19 at 07:39
@Itachi great)) – Sardorbek Imomaliev Aug 07 '19 at 07:55

Custom Serializer and ViewSet for ManyToManyField in DRF

1 Answers1