How to group two same values and get value from other field in django, DRF

Question

I am struggling with grouping two same field values and displaying their related values in one response.

models.py:

class Book(models.Model):
    user = models.ForeignKey(User, on_delete = models.CASCADE, null = True, blank = True)
    image = models.ImageField(default = "Nana.jpg", upload_to = 'images/', null = True, blank = True)
    title = models.CharField(max_length = 150, unique = True)
    author = models.CharField(max_length = 100)
    category = models.CharField(max_length = 100)
    description = models.TextField(max_length = 5000, null = True, blank = True)
    published_date = models.DateField(null = True, blank = True)
    language = models.CharField(max_length = 100, null = True, blank = True, default = "Not selected")
    read_book_count = models.IntegerField(default = 0)


    def __str__(self):
        return self.title

Views.py:

class BookAuthors(APIView):

def get(self, request):
    author = Book.objects.all()
    serializer = AuthorSerializer(author, many = True)
    return Response(serializer.data)

serializers.py

class AuthorSerializer(serializers.ModelSerializer):
    class Meta:
        model = Book
        fields = ['title', 'author']

urls.py

path('library/api/authors/', views.BookAuthors.as_view()),

I want to combine author Homer and his two titles in same place not to be separated.

Asked By: Stefan Vukovic

||

Source

Answer 1

You need to use the query with distinct authors and change your serializer.

Views.py

class BookAuthors(APIView):

def get(self, request):
    author = Book.objects.distinct('author')
    serializer = AuthorSerializer(author, many = True)
    return Response(serializer.data)

serializers.py

class AuthorSerializer(serializers.ModelSerializer):
    titles = serializers.SerializerMethodField()

    class Meta:
        model = Book
        fields = ['author', 'titles']

    def get_titles(self, book):
        return list(Book.objects.filter(author=book.author).values_list('title', flat=True))

Output will be like this

[
    ...
    
    {
        "author": "author1",
         "titles": ["title1", "title2"]

    },

    ...

]

Answered By: Asad Mahmood

Answer 2

You can solve your problem by using values method that groups your rows depend on fields you pass to it. So the code becomes something like this:

(Just note that ArrayAgg can be used only with PostgreSQL)

views.py

from django.contrib.postgres.aggregates import ArrayAgg

class BookAuthors(APIView):
    def get(self, request):
        authors = Book.objects 
            .values('author') 
            .annotate(titles=ArrayAgg('title'))
        serializer = AuthorSerializer(authors, many=True)
        return Response(serializer.data)

serializer.py

class AuthorSerializer(serializers.ModelSerializer):
    titles = serializers.ListField(child=serializers.CharField())

    class Meta:
        model = Book
        fields = ['titles', 'author']

Answered By: Amrez

How to group two same values and get value from other field in django, DRF

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