How to get Total Children in a Parent Serializer

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I want to display the total number of Workers associated with a Ticket Counter in a parent (Ticket counter) serializer.

Below are the two Serializers:

class TicketCounterSerializer(serializers.ModelSerializer):
 workers = WorkerToCounterSerializer(many=True, read_only=True)    
 class Meta:
     model = TicketCounter
     fields = (
               'ticket_counter_name',
               'ticket_counter_description',
               'ticket_counter_address',
               'workers',
               )


class WorkerToCounterSerializer(serializers.ModelSerializer):
 class Meta:
     model = WorkerToTicketCounter
     fields = (
         'user',
         'ticket_counter',
         'worker',
     )

MODELS:

class TicketCounter(models.Model):
   user = models.ForeignKey(User, on_delete=models.CASCADE)
   ticket_counter_name = models.CharField(max_length=100, default="")
   ticket_counter_description = models.CharField(max_length=1500, default="")
   ticket_counter_address = models.CharField(max_length=1500, default="")


class WorkerToTicketCounter(models.Model):
   user = models.ForeignKey(User, on_delete=models.CASCADE)
   ticket_counter = models.ForeignKey(TicketCounter,related_name="workers")
   worker = models.ForeignKey(User,related_name='worker_for_ticket_counter')

Here is how I am getting result:

{
        "ticket_counter_name": "First",
        "ticket_counter_description": "firsty",
        "ticket_counter_address": "222fdssssss",
        "workers": [
            {
                "user": 1,
                "ticket_counter": 3,
                "worker": 4,

            },
            {
                "user": 1,
                "ticket_counter": 3,
                "worker": 5,

            },

        ]
 }

Here is how I want

{
        "ticket_counter_name": "First",
        "ticket_counter_description": "firsty",
        "ticket_counter_address": "222fdssssss",
        "workers": 2 # just the total count
 }

How to just display the total count?

django-serializer django-rest-framework django
1 Answers

You can do this with an annotation, and serialize it as an IntegerField, like:

class TicketCounterSerializer(serializers.ModelSerializer):
    num_workers = serializers.IntegerField()
    class Meta:
        model = TicketCounter
        fields = (
            'ticket_counter_name',
            'ticket_counter_description',
            'ticket_counter_address',
            'num_workers',
         )

In the ViewSet, we can then specify:

from django.db.models import Count

class TicketCounterViewSet(viewsets.ListApiView):
    queryset = TicketCounter.objects.annotate(num_workers=Count('workers'))
    serializer_class = TicketCounterSerializer

We thus annotate every TicketCounter object with an attribute num_workers that contains the number of related WorkerToTicketCounter object.

Personally however I think the modeling has some weird names: the TicketCounter does not really look like a counter. Although I do not know the full scope of your application, I think models named Ticket, and Worker make perhaps more sense.

user_675790
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