Changed work of shelf books

backend/apps/shelf_books/serializers.py

@@ -0,0 +1,84 @@
+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)