Bookモデルにデータ投入時、履歴としてLogモデルにデータを入れたい。

ManyToManyFieldが`含まれない`場合

models.py

from django.db import models

class Auther(models.Model):
    author_name = models.CharField()

class Book(models.Model):

    book_name = models.CharField()
    book_author = models.ForeignKey(Auther)
    
class Log(models.Model):
    message = models.CharField()

serializers.py

from rest_framework import serializers

class BookSerializer(serializers.ModelSerializer):

    class Meta:
        model = Book
        fields = '__all__'

views.py

from rest_framework import viewsets

class BookViewSet(viewsets.ModelViewSet):

    queryset = Book.objects.all()
    serializer_class = serializers.BookSerializer

    def perform_create(self, serializer):
        # Book 保存
        serializer.save()
        # Log 保存
        book_name = serializer.data['book_name']
        book_author = serializer.data['book_author']
        log = Log.objects.create(
            message=f'登録完了({book_name}, {book_author})'
        )
        log.save()

Bookにデータを投入すれば

curl -X 'POST' \
  'http://127.0.0.1:8001/book/' \
  -H 'Content-Type: application/json' \
  -d '{
  "book_name": "TEST",
  "book_author": "TEST",
}'

Log にもデータが投入される

curl -X GET 'http://127.0.0.1:8001/log/'

[
    {
        "id": 1,
        "message": "登録完了(TEST, 1)"
    }
]

ManyToManyFieldが`含まれる`場合

models.py

from django.db import models

class Auther(models.Model):
    author_name = models.CharField()

class Book(models.Model):

    book_name = models.CharField()
    book_authors = models.ManyToManyField(Auther, blank=True)
    

class Log(models.Model):
    message = models.CharField()

serializers.py

from rest_framework import serializers

class BookSerializer(serializers.ModelSerializer):

    class Meta:
        model = Book
        fields = '__all__'

views.py

from rest_framework import viewsets

class BookViewSet(viewsets.ModelViewSet):

    queryset = Book.objects.all()
    serializer_class = serializers.BookSerializer

    def perform_create(self, serializer):
        # Book 保存
        serializer.save()
        # Log 保存
        book_name = serializer.data['book_name']
        for author_id in serializer.data['book_authors']:
            log = Log.objects.create(
                message=f'登録完了({book_name}, {author_id})',
            )
            log.save()

Bookにデータを投入すれば

curl -X 'POST' \
  'http://127.0.0.1:8001/book/' \
  -H 'Content-Type: application/json' \
  -d '{
  "book_name": "TEST",
  "book_authors": "[1,2]",
}'

Log にもデータが投入される

curl -X GET 'http://127.0.0.1:8001/log/'

[
    {
        "id": 1,
        "message": "登録完了(TEST, 1)"
    },
    {
        "id": 2,
        "message": "登録完了(TEST, 2)"
    },
]