usage spring data jpa with query dsl

-- dependency

<!-- query dsl dependency -->
<dependency>
  <groupId>com.querydsl</groupId>
  <artifactId>querydsl-apt</artifactId>
</dependency>

<dependency>
  <groupId>com.querydsl</groupId>
  <artifactId>querydsl-jpa</artifactId>
</dependency>

<!-- plugin set-->
<plugins>
 <plugin>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-maven-plugin</artifactId>
 </plugin>
 <plugin>
  <groupId>com.mysema.maven</groupId>
  <artifactId>apt-maven-plugin</artifactId>
  <version>1.1.3</version>
 <executions>
  <execution>
   <goals>
    <goal>process</goal>
   </goals>
   <configuration>
    <outputDirectory>target/generated-sources/java</outputDirectory>
    <processor>com.querydsl.apt.jpa.JPAAnnotationProcessor</processor>
   </configuration>
  </execution>
 </executions>
 </plugin>
</plugins>

-- created databaseConfig.java

@Configuration
public class Databaseconfig {
    @Bean
    public JPAQueryFactory queryFactory(EntityManager em) {
        return new JPAQueryFactory(em);
    }
}

 

-- created entity [author <1 - *> book]

// Entity Author
@Getter
@NoArgsConstructor(access = AccessLevel.PROTECTED)
@Entity
@Table
public class Author{
    @Id
    private authorSeq;
    private long author;
    private String name;
}

// Entity Book
@Getter
@EqualsAndHashCode(of = {"bookSeq"}, callSuper = false)
@Entity
@Table
public class Book{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long  bookSeq;
	private String title;
    private String description;
    private LocalDate published;
    private long rate;
    
    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "authorSeq")
    private Author author;
}

- book DTO

@Getter
@NoArgsConstructor
public class YoutubeDTO {

    private String name;
    private String title;
    private String description;
    private long rate;
    private LocalDateTime publiched;
   
    @QueryProjection
    @Builder
    public BookDTO(String name,
    		String title,
            String description,
            long rate,
            LocalDate published) {
        this.name = name;
        this.title = title;
        this.description = description;
        this.rate = rate;
        this.published = published;
    }
}

-- author repository

@Repository
public interface AuthorRepository extends JpaRepository<Author, Long>, 
		QuerydslPredicateExecutor<Author> {
}

-- book repository

public interface BookRepository extends JpaRepository<Book, Long>,
        BookRepositoryCustom,QuerydslPredicateExecutor<Book> {
}

-- custom repository

public interface BookRepositoryCustom {
    Page<BookDTO> findRateTop(Pageable pageable);
}

-- implementation custom repository

//평점 과 출판 일 을 기준으로 정렬 하여 페이징 처리하여 가져오도록 한다.
@RequiredArgsConstructor
public class BookRepositoryImpl implements BookRepositoryCustom{
    private final JPAQueryFactory queryFactory;
    @Override
    public Page<BookDTO> findRateTop(Pageable pageable) {
        QBook book = QBook.book;
        QAuthor author = QAuthor.author;
        QueryResults<BookDTO> result = queryFactory
                .select(
                Projections.fields(
                BookDTO.class,
                  author.name,
                  book.title,
                  book.description,
                  book.rate,
                  book.published))
                .from(book)
                .leftJoin(author)
                .on(author.authorSeq.eq(book.author.authorSeq))
                .groupBy(book.author.authorSeq)
                .orderBy(book.rate.asc(),book.published.desc())
                .offset(pageable.getOffset())
                .limit(pageable.getPageSize())
                .fetchResults();
        return result.isEmpty() ? Page.empty() : 
        	new PageImpl<>(result.getResults(),pageable,result.getTotal());
    }
}

 

- Predicate 구현

public class BookPredicate {
    public static Predicate byTitle(String title) {
		QBook book = QBook.book;
        BooleanBuilder builder = new BooleanBuilder();
        return builder.and(book.title.likeIgnoreCase(title));
    }
}

- Predicate 사용

@Slf4j
@Service
public class BookService {
    @Autowired
    private BookRepository bookRepository;
    
    @Override
    public Optional<Book> findByTitle(String title) {
        return bookRepository.findOne(BookPredicate.byTitle(title));
    }
}