CODEWITHSUNDEEP
pythondjangodjango-rest-framework
Dawid Łychoński
Dawid Łychoński

Reputation: 71

Serialize relations in django

I have 2 models --> Candidate and Grade. 1 Candidate have many Grade. I want to return from rest API average grade from many grades that one Candidate can receive. How can I doing this.

My model:

class Candidate(models.Model):
   first_name = models.CharField(max_length=50)
   last_name = models.CharField(max_length=50)

class Grade(models.Model):
   value = models.IntegerField(blank=True, null=True)
   candidate = models.ForeignKey(Candidate, on_delete=models.CASCADE, related_name='grades')

My serializers.py

from rest_framework import serializers
from .models import Candidate, Grade


class CandidateSerializer(serializers.ModelSerializer):

   pk = serializers.SerializerMethodField('get_pk_from_candidate')
   full_name = serializers.SerializerMethodField('get_full_name_from_candidate')
   grades = serializers.SlugRelatedField(many=True, read_only=True, slug_field='value')
   
   class Meta: 
    
      model = Candidate
 
      fields = ['pk', 'full_name', 'avg_grade', 'grades']

  
   def get_pk_from_candidate(self, candidate):
      return candidate.id

   
   def get_full_name_from_candidate(self, candidate):
      data = (candidate.first_name, candidate.last_name)
      full_name = ' '.join(data)

      return full_name

I want my JSON format like below:

{
      "pk": 3,
      "full_name": "rafał małek",
      "avg_grade": "",
      "grades": [
        12,
        4,
        13,
        5
      ]
    },

Upvotes: 0

Views: 80

Answers (2)

JPG
JPG

Reputation: 88659

Use serializers.SerializerMethodField as


from django.db.models import Avg


class CandidateSerializer(serializers.ModelSerializer):
    pk = serializers.SerializerMethodField('get_pk_from_candidate')
    full_name = serializers.SerializerMethodField('get_full_name_from_candidate')
    grades = serializers.SlugRelatedField(many=True, read_only=True, slug_field='value')
    avg_grade = serializers.SerializerMethodField()

    def get_avg_grade(self, candidate):
        return candidate.grades.aggregate(avg_value=Avg('value')).get("avg_value")

    class Meta:
        model = Candidate

        fields = ['pk', 'full_name', 'avg_grade', 'grades']

    def get_pk_from_candidate(self, candidate):
        return candidate.id

    def get_full_name_from_candidate(self, candidate):
        data = (candidate.first_name, candidate.last_name)
        full_name = ' '.join(data)

        return full_name

Upvotes: 1

rollingthedice
rollingthedice

Reputation: 1125

You can use a SerializerMethodField() and ORM's Aggregation(doc) with Avg.

from django.db.models import Avg
from rest_framework import serializers
from .models import Candidate, Grade


class CandidateSerializer(serializers.ModelSerializer):
   pk = serializers.SerializerMethodField('get_pk_from_candidate')
   full_name = serializers.SerializerMethodField('get_full_name_from_candidate')
   avg_grade = serializers.SerializerMethodField('get_avg_grade')
   grades = serializers.SlugRelatedField(many=True, read_only=True, slug_field='value')
   
   class Meta: 
      model = Candidate
      fields = ['pk', 'full_name', 'avg_grade', 'grades']

  
   def get_pk_from_candidate(self, candidate):
      return candidate.id

   
   def get_full_name_from_candidate(self, candidate):
      data = (candidate.first_name, candidate.last_name)
      full_name = ' '.join(data)

      return full_name

   def get_avg_grade(self, candidate):
       return candidate.grades.aggregate(Avg('value'))['value__avg']

Upvotes: 1

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