How to add count of pending tasks to List Json - django

Question

I am creating a todo list API(backend) in django rest framework. I have two models List and Task
#models.py
from django.db import models
# Create your models here.
class List(models.Model):
list_name = models.CharField(max_length=200)
def __str__(self):
return self.list_name
class Meta:
db_table = 'list'
class Task(models.Model):
todo_list = models.ForeignKey(List, on_delete=models.CASCADE)
task_name = models.CharField(max_length=500)
due_date = models.DateField()
done = models.BooleanField(default=False)
def __str__(self):
return self.task_name
class Meta:
db_table = 'task'
The serializers file,
#serializers.py
from rest_framework import serializers
from rest_framework_serializer_extensions.serializers import SerializerExtensionsMixin
from .models import List, Task
class ListSerializer(SerializerExtensionsMixin, serializers.ModelSerializer):
class Meta:
model = List
fields = "__all__"
class TaskSerializer(SerializerExtensionsMixin, serializers.ModelSerializer):
class Meta:
model = Task
fields = "__all__"
expandable_fields = dict(
todolist=ListSerializer
)
My todo list app will have multiple lists and each list have multiple tasks. Each task will have a due date and can be marked as done. I am trying to add the number of pending tasks to my List json. How do I go about doing that?

Answer 1

You can add a new field using SerializerMethodField:
class ListSerializer(SerializerExtensionsMixin, serializers.ModelSerializer):
pending_count = serializers.SerializerMethodField()
class Meta:
model = List
fields = "__all__"
def get_pending_count(self, obj):
return obj.task_set.filter(done=False).count()