BAEL-5547: added code for specifications join (#12212)

* BAEL-5547: added code for specifications join

* BAEL-5547: renamed test class and formatted the code

persistence-modules/spring-data-jpa-query-3/src/main/java/com/baeldung/spring/data/jpa/query/specifications/join/Author.java

@@ -0,0 +1,57 @@
+package com.baeldung.spring.data.jpa.query.specifications.join;
+
+import javax.persistence.*;
+
+import java.util.List;
+
+@Entity
+public class Author {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    private String firstName;
+
+    private String lastName;
+
+    @OneToMany(cascade = CascadeType.ALL)
+    private List<Book> books;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public void setLastName(String lastName) {
+        this.lastName = lastName;
+    }
+
+    public List<Book> getBooks() {
+        return books;
+    }
+
+    public void setBooks(List<Book> books) {
+        this.books = books;
+    }
+
+    @Override
+    public String toString() {
+        return "Author{" + "id=" + id + ", firstName='" + firstName + '\'' + ", lastName='" + lastName + '\'' + ", books=" + books + '}';
+    }
+}

persistence-modules/spring-data-jpa-query-3/src/main/java/com/baeldung/spring/data/jpa/query/specifications/join/AuthorSpecifications.java

@@ -0,0 +1,24 @@
+package com.baeldung.spring.data.jpa.query.specifications.join;
+
+import org.springframework.data.jpa.domain.Specification;
+
+import javax.persistence.criteria.*;
+
+public class AuthorSpecifications {
+
+    public static Specification<Author> hasFirstNameLike(String name) {
+        return (root, query, criteriaBuilder) -> criteriaBuilder.like(root.<String>get("firstName"), "%" + name + "%");
+    }
+
+    public static Specification<Author> hasLastName(String name) {
+        return (root, query, cb) -> cb.equal(root.<String>get("lastName"), name);
+    }
+
+    public static Specification<Author> hasBookWithTitle(String bookTitle) {
+        return (root, query, criteriaBuilder) -> {
+            Join<Book, Author> authorsBook = root.join("books");
+            return criteriaBuilder.equal(authorsBook.get("title"), bookTitle);
+        };
+    }
+
+}

persistence-modules/spring-data-jpa-query-3/src/main/java/com/baeldung/spring/data/jpa/query/specifications/join/AuthorsRepository.java

@@ -0,0 +1,9 @@
+package com.baeldung.spring.data.jpa.query.specifications.join;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.JpaSpecificationExecutor;
+import org.springframework.stereotype.Repository;
+
+@Repository
+public interface AuthorsRepository extends JpaRepository<Author, Long>, JpaSpecificationExecutor<Author> {
+}

persistence-modules/spring-data-jpa-query-3/src/main/java/com/baeldung/spring/data/jpa/query/specifications/join/Book.java

@@ -0,0 +1,37 @@
+package com.baeldung.spring.data.jpa.query.specifications.join;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+
+@Entity
+public class Book {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    private String title;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    @Override
+    public String toString() {
+        return "Book{" + "id=" + id + ", title='" + title + '\'' + '}';
+    }
+}

persistence-modules/spring-data-jpa-query-3/src/test/java/com/baeldung/spring/data/jpa/query/specifications/join/SpecificationsJoinIntegrationTest.java

@@ -0,0 +1,80 @@
+package com.baeldung.spring.data.jpa.query.specifications.join;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
+import org.springframework.data.jpa.domain.Specification;
+import org.springframework.test.context.junit4.SpringRunner;
+
+import java.util.Arrays;
+import java.util.List;
+
+import static com.baeldung.spring.data.jpa.query.specifications.join.AuthorSpecifications.*;
+import static org.assertj.core.api.Assertions.assertThat;
+
+@RunWith(SpringRunner.class)
+@DataJpaTest
+public class SpecificationsJoinIntegrationTest {
+
+    @Autowired
+    private AuthorsRepository repository;
+
+    @Before
+    public void beforeEach() {
+        saveTestData();
+    }
+
+    @Test
+    public void whenSearchingByLastName_thenOneAuthorIsReturned() {
+
+        List<Author> authors = repository.findAll(hasLastName("Martin"));
+
+        assertThat(authors).hasSize(1);
+    }
+
+    @Test
+    public void whenSearchingByLastNameAndFirstNameLike_thenOneAuthorIsReturned() {
+
+        Specification<Author> specification = hasLastName("Martin").and(hasFirstNameLike("Robert"));
+
+        List<Author> authors = repository.findAll(specification);
+
+        assertThat(authors).hasSize(1);
+    }
+
+    @Test
+    public void whenSearchingByBookTitle_thenOneAuthorIsReturned() {
+
+        Specification<Author> specification = hasBookWithTitle("Clean Code");
+
+        List<Author> authors = repository.findAll(specification);
+
+        assertThat(authors).hasSize(1);
+    }
+
+    @Test
+    public void whenSearchingByBookTitleAndAuthorName_thenOneAuthorIsReturned() {
+
+        Specification<Author> specification = hasLastName("Martin").and(hasBookWithTitle("Clean Code"));
+
+        List<Author> authors = repository.findAll(specification);
+
+        assertThat(authors).hasSize(1);
+    }
+
+    private void saveTestData() {
+        Author uncleBob = new Author();
+        uncleBob.setFirstName("Robert");
+        uncleBob.setLastName("Martin");
+
+        Book book1 = new Book();
+        book1.setTitle("Clean Code");
+        Book book2 = new Book();
+        book2.setTitle("Clean Architecture");
+
+        uncleBob.setBooks(Arrays.asList(book1, book2));
+        repository.save(uncleBob);
+    }
+}