rest framework alter data before serializing code example

Example 1: serializers.validationerror django

class HighScoreSerializer(serializers.BaseSerializer):
    def to_internal_value(self, data):
        score = data.get('score')
        player_name = data.get('player_name')

        # Perform the data validation.
        if not score:
            raise serializers.ValidationError({
                'score': 'This field is required.'
            })
        if not player_name:
            raise serializers.ValidationError({
                'player_name': 'This field is required.'
            })
        if len(player_name) > 10:
            raise serializers.ValidationError({
                'player_name': 'May not be more than 10 characters.'
            })

        # Return the validated values. This will be available as
        # the `.validated_data` property.
        return {
            'score': int(score),
            'player_name': player_name
        }

    def to_representation(self, instance):
        return {
            'score': instance.score,
            'player_name': instance.player_name
        }

    def create(self, validated_data):
        return HighScore.objects.create(**validated_data)

Example 2: how to add methods to manuplate the model in serializers

from rest_framework import serializers, status
from models import *


class UserSerializer(serializers.ModelSerializer):
    class Meta:
        model = User
        fields = ('username', 'first_name', 'last_name', 'email')


class StudentSerializer(serializers.ModelSerializer):
    """
    A student serializer to return the student details
    """
    user = UserSerializer(required=True)

    class Meta:
        model = UnivStudent
        fields = ('user', 'subject_major',)

    def create(self, validated_data):
        """
        Overriding the default create method of the Model serializer.
        :param validated_data: data containing all the details of student
        :return: returns a successfully created student record
        """
        user_data = validated_data.pop('user')
        user = UserSerializer.create(UserSerializer(), validated_data=user_data)
        student, created = UnivStudent.objects.update_or_create(user=user,
                            subject_major=validated_data.pop('subject_major'))
        return student