added AfterMapping in BookMapper, to set categories into Book

src/main/java/book/store/dto/request/CreateBookRequestDto.java

@@ -20,5 +20,5 @@ public class CreateBookRequestDto {
     private String description;
     private String coverImage;
     @NotNull
-    private Set<Long> categoriesIds;
+    private Set<Long> categoryIds;
 }

src/main/java/book/store/dto/response/BookDto.java

@@ -13,5 +13,5 @@ public class BookDto {
     private BigDecimal price;
     private String description;
     private String coverImage;
-    private Set<Long> categoriesIds;
+    private Set<Long> categoryIds;
 }

src/main/java/book/store/mapper/BookMapper.java

@@ -6,6 +6,8 @@
 import book.store.dto.response.BookDtoWithoutCategoryIds;
 import book.store.model.Book;
 import book.store.model.Category;
+import java.util.HashSet;
+import java.util.Set;
 import java.util.stream.Collectors;
 import org.mapstruct.AfterMapping;
 import org.mapstruct.Mapper;
@@ -14,18 +16,30 @@
 
 @Mapper(config = MapperConfig.class)
 public interface BookMapper {
-    @Mapping(target = "categoriesIds", ignore = true)
+    @Mapping(target = "categoryIds", ignore = true)
     BookDto toDto(Book book);
 
-    @Mapping(target = "id", ignore = true)
+    @Mapping(target = "categories", ignore = true)
     Book toModel(CreateBookRequestDto createBookRequestDto);
 
     BookDtoWithoutCategoryIds toDtoWithoutCategories(Book book);
 
     @AfterMapping
     default void setCategoryIds(@MappingTarget BookDto bookDto, Book book) {
-        bookDto.setCategoriesIds(book.getCategories().stream()
+        bookDto.setCategoryIds(book.getCategories().stream()
                 .map(Category::getId)
                 .collect(Collectors.toSet()));
     }
+
+    @AfterMapping
+    default void setCategoriesIntoBook(@MappingTarget Book book,
+                                       CreateBookRequestDto createBookRequestDto) {
+        Set<Category> categories = new HashSet<>();
+        for (Long categoryId : createBookRequestDto.getCategoryIds()) {
+            Category category = new Category();
+            category.setId(categoryId);
+            categories.add(category);
+        }
+        book.setCategories(categories);
+    }
 }

src/main/java/book/store/repository/CategoryRepository.java

@@ -1,9 +1,7 @@
 package book.store.repository;
 
 import book.store.model.Category;
-import java.util.Set;
 import org.springframework.data.jpa.repository.JpaRepository;
 
 public interface CategoryRepository extends JpaRepository<Category, Long> {
-    Set<Category> findByIdIn(Set<Long> categoriesIds);
 }

src/main/java/book/store/service/impl/BookServiceImpl.java

@@ -23,9 +23,7 @@ public class BookServiceImpl implements BookService {
 
     @Override
     public BookDto save(CreateBookRequestDto requestDto) {
-        Book book = bookMapper.toModel(requestDto);
-        book.setCategories(categoryRepository.findByIdIn(requestDto.getCategoriesIds()));
-        return bookMapper.toDto(bookRepository.save(book));
+        return bookMapper.toDto(bookRepository.save(bookMapper.toModel(requestDto)));
     }
 
     @Override