Changed work of shelf books

backend/apps/shelf_books/admin.py

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+from django.contrib import admin
+
+# Register your models here.

backend/apps/shelf_books/apps.py

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+from django.apps import AppConfig
+
+
+class ShelfBooksConfig(AppConfig):
+    name = 'apps.shelf_books'

backend/apps/shelf_books/migrations/0001_initial.py

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+# Generated by Django 6.0.3 on 2026-03-22 12:16
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = [
+        ('books', '0001_initial'),
+        ('shelves', '0002_initial'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='ShelfItem',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('quantity', models.PositiveIntegerField(default=0)),
+                ('book', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='shelf_items', to='books.book')),
+                ('shelf', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='book_items', to='shelves.shelf')),
+            ],
+            options={
+                'constraints': [models.UniqueConstraint(fields=('book', 'shelf'), name='unique_book_per_shelf')],
+            },
+        ),
+    ]

backend/apps/shelf_books/migrations/0002_rename_shelfitem_shelfbook.py

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+# Generated by Django 6.0.3 on 2026-03-22 12:53
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('books', '0001_initial'),
+        ('shelf_books', '0001_initial'),
+        ('shelves', '0002_initial'),
+    ]
+
+    operations = [
+        migrations.RenameModel(
+            old_name='ShelfItem',
+            new_name='ShelfBook',
+        ),
+    ]

backend/apps/shelf_books/models.py

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+from django.db.models import Q, F
+from django.db import models
+
+from apps.books.models import Book
+from apps.shelves.models import Shelf
+
+class ShelfBook(models.Model):
+    book = models.ForeignKey(Book, on_delete=models.CASCADE, related_name="shelf_items")
+    shelf = models.ForeignKey(Shelf, on_delete=models.CASCADE, related_name="book_items")
+
+    quantity = models.PositiveIntegerField(default=0)
+
+    class Meta:
+        constraints = [
+            models.UniqueConstraint(
+                fields=["book", "shelf"],
+                name="unique_book_per_shelf"
+            ),
+        ]

backend/apps/shelf_books/serializers.py

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+from rest_framework import serializers
+
+from apps.shelf_books.models import ShelfBook
+from apps.books.models import Book
+from apps.shelves.models import Shelf
+from apps.shelves.serializers import ShelfSerializer
+from apps.books.serializers import BookSerializer
+
+class ShelfBookSerializer(serializers.ModelSerializer):
+    shelf = ShelfSerializer(read_only=True)
+
+    book = BookSerializer(read_only=True)
+    book_id = serializers.PrimaryKeyRelatedField(
+        queryset=Book.objects.all(),
+        source="book", 
+        write_only=True
+    )
+
+    class Meta:
+        model = ShelfBook
+        fields = [
+            "id",
+            "shelf",
+            "book",
+            "book_id",
+            "quantity"
+        ]
+        read_only_fields = ["id"]
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+
+        request = self.context.get("request")        
+        if request and request.user and request.user.is_authenticated:
+            self.fields["book_id"].queryset = Book.objects.filter(
+                user=request.user
+            )
+        else:
+            self.fields["book_id"].queryset = Book.objects.none()
+            
+
+    def validate(self, attrs):
+        attrs = super().validate(attrs)
+
+        book = attrs.get("book")
+        shelf = self.context.get("shelf")
+
+        if not book:
+            book = self.instance.book
+
+        if not shelf:
+            return attrs
+
+        qs = ShelfBook.objects.filter(
+            book=book,
+            shelf=shelf
+        )
+            
+        if self.instance:
+            qs = qs.exclude(pk=self.instance.pk)
+
+        if qs.exists():
+            raise serializers.ValidationError(
+                "This Book already exists in shelf!"
+            )
+                
+        if book.user_id != shelf.user_id:
+            raise serializers.ValidationError(
+                "Book and Shelf must be from the same user!"
+            )
+        
+        return attrs
+
+    def create(self, validated_data):
+        shelf = self.context["shelf"]
+        validated_data["shelf"] = shelf
+
+        return super().create(validated_data)
+    
+    def update(self, instance, validated_data):
+        shelf = self.context["shelf"]
+        validated_data["shelf"] = shelf
+
+        return super().update(instance, validated_data)

backend/apps/shelf_books/tests.py

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+from django.test import TestCase
+
+# Create your tests here.

backend/apps/shelf_books/urls.py

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+from django.urls import path
+
+from apps.shelf_books.views import ShelfBooks, SelectedShelfBook
+
+urlpatterns = [
+    path("shelves/<int:shelf_id>/books/", ShelfBooks.as_view()),
+    path("shelves/<int:shelf_id>/books/<int:book_id>/", SelectedShelfBook.as_view())
+]
+
+

backend/apps/shelf_books/views.py

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+from rest_framework import generics
+
+from apps.shelf_books.models import ShelfBook
+from apps.shelves.models import Shelf
+from apps.shelf_books.serializers import ShelfBookSerializer
+from rest_framework.permissions import IsAuthenticated
+from rest_framework_simplejwt.authentication import JWTAuthentication
+from drf_spectacular.utils import extend_schema, extend_schema_view
+
+
+@extend_schema_view(
+    get=extend_schema(tags=["Shelf Books"]),
+    post=extend_schema(tags=["Shelf Books"]),
+)
+class ShelfBooks(generics.ListCreateAPIView):
+    queryset = ShelfBook.objects.all()
+    serializer_class =  ShelfBookSerializer
+
+    authentication_classes = [JWTAuthentication]
+    permission_classes = [IsAuthenticated]
+
+    def get_queryset(self):
+        shelf_id = self.kwargs["shelf_id"]
+        
+        return ShelfBook.objects.filter(
+            shelf__id=shelf_id,
+            shelf__user_id=self.request.user.pk,
+        ).select_related("book", "shelf").prefetch_related("book__authors")
+
+    def get_serializer_context(self):
+        context = super().get_serializer_context()
+
+        shelf_id = self.kwargs["shelf_id"]
+
+        shelf = Shelf.objects.filter(
+            id=shelf_id,
+            user=self.request.user
+        ).first()
+
+        context["shelf"] = shelf
+        return context
+
+
+@extend_schema_view(
+    get=extend_schema(tags=["Shelf Books"]),
+    put=extend_schema(tags=["Shelf Books"]),
+    patch=extend_schema(tags=["Shelf Books"]),
+    delete=extend_schema(tags=["Shelf Books"]),
+)
+class SelectedShelfBook(generics.RetrieveUpdateDestroyAPIView):
+    queryset = ShelfBook.objects.all()
+    serializer_class =  ShelfBookSerializer
+
+    authentication_classes = [JWTAuthentication]
+    permission_classes = [IsAuthenticated]
+
+    lookup_url_kwarg = "book_id"
+
+    def get_queryset(self):
+        return ShelfBook.objects.filter(
+            shelf_id=self.kwargs["shelf_id"],
+            shelf__user=self.request.user,
+        ).select_related("book", "shelf").prefetch_related("book__authors")    
+    
+    def get_object(self):
+        queryset = self.get_queryset()
+
+        return generics.get_object_or_404(
+            queryset,
+            book_id=self.kwargs["book_id"]
+        )
+        
+    def get_serializer_context(self):
+        context = super().get_serializer_context()
+
+        shelf = Shelf.objects.filter(
+            id=self.kwargs["shelf_id"],
+            user=self.request.user
+        ).first()
+
+        context["shelf"] = shelf
+        return context
+
+