Spring projections including collections

Author: AnghelLeonard

HibernateSpringBootProjectionAndCollections/src/main/java/com/bookstore/MainApplication.java

@@ -44,6 +44,10 @@ public ApplicationRunner init() {
             System.out.println("\n\nFetch authors with books via array of objects and transform to DTO:");
             System.out.println("-----------------------------------------------------------------");
             bookstoreService.fetchAuthorsWithBooksViaArrayOfObjectsAndTransformToDto();                          
+            
+            System.out.println("\n\nFetch authors with books via JdbcTemplate as DTO:");
+            System.out.println("-----------------------------------------------------------------");
+            bookstoreService.fetchAuthorsWithBooksViaJdbcTemplateToDto();                          
         };
     }
 }

HibernateSpringBootProjectionAndCollections/src/main/java/com/bookstore/controller/BookstoreController.java

@@ -46,4 +46,9 @@ public List<Object[]> fetchAuthorsWithBooksViaArrayOfObjects() {
     public List<com.bookstore.transform.dto.AuthorDto> fetchAuthorsWithBooksViaArrayOfObjectsAndTransformToDto() {
         return bookstoreService.fetchAuthorsWithBooksViaArrayOfObjectsAndTransformToDto();
     }
+    
+    @GetMapping("/authorsAndbooks/7")
+    public List<com.bookstore.jdbcTemplate.dto.AuthorDto> fetchAuthorsWithBooksViaJdbcTemplateToDto() {
+        return bookstoreService.fetchAuthorsWithBooksViaJdbcTemplateToDto();
+    }
 }

HibernateSpringBootProjectionAndCollections/src/main/java/com/bookstore/jdbcTemplate/dto/AuthorDto.java

@@ -0,0 +1,66 @@
+package com.bookstore.jdbcTemplate.dto;
+
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.List;
+
+public class AuthorDto implements Serializable {
+
+    private static final long serialVersionUID = 1L;
+
+    private Long authorId;
+    private String name;
+    private String genre;
+
+    private List<BookDto> books = new ArrayList<>();
+
+    public AuthorDto() {
+    }
+
+    public AuthorDto(Long authorId, String name, String genre) {
+        this.authorId = authorId;
+        this.name = name;
+        this.genre = genre;
+    }
+
+    public Long getId() {
+        return authorId;
+    }
+
+    public void setId(Long authorId) {
+        this.authorId = authorId;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getGenre() {
+        return genre;
+    }
+
+    public void setGenre(String genre) {
+        this.genre = genre;
+    }
+
+    public List<BookDto> getBooks() {
+        return books;
+    }
+
+    public void setBooks(List<BookDto> books) {
+        this.books = books;
+    }
+
+    public void addBook(BookDto book) {
+        books.add(book);
+    }
+
+    @Override
+    public String toString() {
+        return "AuthorDto{" + "authorId=" + authorId + ", name=" + name + ", genre=" + genre + '}';
+    }
+}

HibernateSpringBootProjectionAndCollections/src/main/java/com/bookstore/jdbcTemplate/dto/AuthorExtractor.java

@@ -0,0 +1,53 @@
+package com.bookstore.jdbcTemplate.dto;
+
+import java.sql.ResultSet;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import org.springframework.jdbc.core.JdbcTemplate;
+import org.springframework.stereotype.Repository;
+import org.springframework.transaction.annotation.Transactional;
+
+@Repository
+@Transactional(readOnly = true)
+public class AuthorExtractor {
+
+    private final JdbcTemplate jdbcTemplate;
+
+    public AuthorExtractor(JdbcTemplate jdbcTemplate) {
+        this.jdbcTemplate = jdbcTemplate;
+    }
+
+    public List<AuthorDto> extract() {
+
+        String sql = "SELECT a.id, a.name, a.genre, b.id, b.title "
+                + "FROM author a INNER JOIN book b ON a.id = b.author_id";
+
+        List<AuthorDto> result = jdbcTemplate.query(sql, (ResultSet rs) -> {
+
+            final Map<Long, AuthorDto> authorsMap = new HashMap<>();
+            while (rs.next()) {
+                Long authorId = (rs.getLong("id"));
+                AuthorDto author = authorsMap.get(authorId);
+                if (author == null) {
+                    author = new AuthorDto();
+                    author.setId(rs.getLong("id"));
+                    author.setName(rs.getString("name"));
+                    author.setGenre(rs.getString("genre"));
+                }
+
+                BookDto book = new BookDto();
+                book.setId(rs.getLong("id"));
+                book.setTitle(rs.getString("title"));
+
+                author.addBook(book);
+                authorsMap.putIfAbsent(author.getId(), author);
+            }
+
+            return new ArrayList<>(authorsMap.values());
+        });
+
+        return result;
+    }
+}

HibernateSpringBootProjectionAndCollections/src/main/java/com/bookstore/jdbcTemplate/dto/BookDto.java

@@ -0,0 +1,41 @@
+package com.bookstore.jdbcTemplate.dto;
+
+import java.io.Serializable;
+
+public class BookDto implements Serializable {
+
+    private static final long serialVersionUID = 1L;
+
+    private Long bookId;
+    private String title;
+
+    public BookDto() {
+    }
+
+    public BookDto(Long bookId, String title) {
+        this.bookId = bookId;
+        this.title = title;
+    }
+
+    public Long getId() {
+        return bookId;
+    }
+
+    public void setId(Long bookId) {
+        this.bookId = bookId;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    @Override
+    public String toString() {
+        return "BookDto{" + "bookId="
+                + bookId + ", title=" + title + '}';
+    }
+}

HibernateSpringBootProjectionAndCollections/src/main/java/com/bookstore/service/BookstoreService.java

@@ -1,5 +1,6 @@
 package com.bookstore.service;
 
+import com.bookstore.jdbcTemplate.dto.AuthorExtractor;
 import com.bookstore.spring.dto.AuthorDto;
 import com.bookstore.spring.dto.SimpleAuthorDto;
 import com.bookstore.repository.AuthorRepository;
@@ -21,17 +22,20 @@ public class BookstoreService {
 
     private final AuthorRepository authorRepository;
     private final AuthorTransformer authorTransformer;
+    private final AuthorExtractor authorExtractor;
 
     @PersistenceContext
     private final EntityManager entityManager;
 
     public BookstoreService(AuthorRepository authorRepository,
             AuthorTransformer authorTransformer,
+            AuthorExtractor authorExtractor,
             EntityManager entityManager) {
 
         this.authorRepository = authorRepository;
         this.entityManager = entityManager;
         this.authorTransformer = authorTransformer;
+        this.authorExtractor = authorExtractor;
     }
 
     @Transactional(readOnly = true)
@@ -119,6 +123,22 @@ public List<com.bookstore.transform.dto.AuthorDto> fetchAuthorsWithBooksViaArray
         return authorsDto;
     }
 
+    @Transactional(readOnly = true)
+    public List<com.bookstore.jdbcTemplate.dto.AuthorDto> fetchAuthorsWithBooksViaJdbcTemplateToDto() {
+
+        List<com.bookstore.jdbcTemplate.dto.AuthorDto> authors = authorExtractor.extract();
+        
+        System.out.println("\nResult set:");
+        authors.forEach(a -> {
+            System.out.println("\n\n" + a.getName() + ", " + a.getGenre());
+            a.getBooks().forEach(b -> System.out.print(b.getTitle() + ", "));
+        });
+
+        briefOverviewOfPersistentContextContent();
+
+        return authors;
+    }
+
     private void briefOverviewOfPersistentContextContent() {
         org.hibernate.engine.spi.PersistenceContext persistenceContext = getPersistenceContext();