How i can serialized data to json with drf serializer - django

Question

I have data models like:
from django.db import models
class Student(models.Model):
first_name = models.CharField(max_length=50)
last_name = models.CharField(max_length=50)
email = models.EmailField()
def __str__(self):
return self.first_name + ' ' + self.last_name
class Course(models.Model):
name = models.CharField(max_length=255)
description = models.TextField()
start_date = models.DateField(null=True)
end_date = models.DateField(null=True)
def __str__(self):
return self.name
class CourseParticipant(models.Model):
course = models.ForeignKey(Course, related_name='courses', on_delete=None)
student = models.ForeignKey(Student, related_name='students', on_delete=None)
completed = models.BooleanField(null=True, default=False)
def __str__(self):
return self.course
I have some serializer like:
class CourseSerializer(serializers.ModelSerializer):
class Meta:
model = Course
fields = ('name', 'end_date', 'start_date')
I need return data in json like:
{
"courses": [
{
"name": "Math",
"end_date": "2019-06-26",
"start_date": "2019-06-26",
"participant_students_count: 10
}
]
}
How I can get "participant_students_count" and return its data in json with other fields.
Thanks for help!

Answer 1

You can use SerializerMethodField of DRF serializer field. Also, see about how to follow Backward access of Foreign key relationship.
from rest_framework import serializers
class CourseSerializer(serializers.ModelSerializer):
participant_students_count = serializers.SerializerMethodField()
class Meta:
model = Course
fields = ('name', 'end_date', 'start_date', 'participant_students_count')
def get_participant_students_count(self, obj):
return obj.courseparticipant_set.count()

Answer 2

class CourseSerializer(serializers.ModelSerializer):
participant_students_count = serializers.SerializerMethodField()
def get_participant_students_count(self, obj):
return CourseParticipant.objects.filter(course=obj).count()
class Meta:
model = Course
fields = ('name', 'end_date', 'start_date', 'participant_students_count')