PR-BAEL-2816 (#7733)

* implement hexagonal architecture pattern

* Add source code for article BAEL-2463

* add source code for article BAEL-2816

* remove irrelevant code

* Remove unnecessary default constructors

* Refactor equals and hashCode methods in Java 7+ way

* Remove equals and hashCode implementations

* Change test methods conventional order

* change saveRelation method to private

To make the code more clean and readable

persistence-modules/hibernate-mapping/src/main/java/com/baeldung/hibernate/wherejointable/Group.java

@@ -0,0 +1,56 @@
+package com.baeldung.hibernate.wherejointable;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.Id;
+import javax.persistence.ManyToMany;
+
+@Entity(name = "e_group")
+public class Group {
+
+    @Id
+    @GeneratedValue
+    private Long id;
+
+    private String name;
+
+    @ManyToMany(mappedBy = "groups")
+    private List<User> users = new ArrayList<>();
+
+    public Group(String name) {
+        this.name = name;
+    }
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public List<User> getUsers() {
+        return users;
+    }
+
+    public void setUsers(List<User> users) {
+        this.users = users;
+    }
+
+    @Override
+    public String toString() {
+        return "Group [name=" + name + "]";
+    }
+
+}

persistence-modules/hibernate-mapping/src/main/java/com/baeldung/hibernate/wherejointable/User.java

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+package com.baeldung.hibernate.wherejointable;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.Id;
+import javax.persistence.JoinColumn;
+import javax.persistence.JoinTable;
+import javax.persistence.ManyToMany;
+
+import org.hibernate.annotations.WhereJoinTable;
+
+@Entity
+public class User {
+
+    @Id
+    @GeneratedValue
+    private Long id;
+
+    private String name;
+
+    @ManyToMany
+    @JoinTable(name = "r_user_group", joinColumns = @JoinColumn(name = "user_id"), inverseJoinColumns = @JoinColumn(name = "group_id"))
+    private List<Group> groups = new ArrayList<>();
+
+    @WhereJoinTable(clause = "role='MODERATOR'")
+    @ManyToMany
+    @JoinTable(name = "r_user_group", joinColumns = @JoinColumn(name = "user_id"), inverseJoinColumns = @JoinColumn(name = "group_id"))
+    private List<Group> moderatorGroups = new ArrayList<>();
+
+    public User(String name) {
+        this.name = name;
+    }
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public List<Group> getGroups() {
+        return groups;
+    }
+
+    public void setGroups(List<Group> groups) {
+        this.groups = groups;
+    }
+
+    public void setModeratorGroups(List<Group> moderatorGroups) {
+        this.moderatorGroups = moderatorGroups;
+    }
+
+    public List<Group> getModeratorGroups() {
+        return moderatorGroups;
+    }
+
+    @Override
+    public String toString() {
+        return "User [name=" + name + "]";
+    }
+
+}

persistence-modules/hibernate-mapping/src/main/java/com/baeldung/hibernate/wherejointable/UserGroupRelation.java

@@ -0,0 +1,31 @@
+package com.baeldung.hibernate.wherejointable;
+
+import java.io.Serializable;
+
+import javax.persistence.Column;
+import javax.persistence.Entity;
+import javax.persistence.EnumType;
+import javax.persistence.Enumerated;
+import javax.persistence.Id;
+
+@Entity(name = "r_user_group")
+public class UserGroupRelation implements Serializable {
+
+    @Id
+    @Column(name = "user_id", insertable = false, updatable = false)
+    private final Long userId;
+
+    @Id
+    @Column(name = "group_id", insertable = false, updatable = false)
+    private final Long groupId;
+
+    @Enumerated(EnumType.STRING)
+    private final UserGroupRole role;
+
+    public UserGroupRelation(Long userId, Long groupId, UserGroupRole role) {
+        this.userId = userId;
+        this.groupId = groupId;
+        this.role = role;
+    }
+
+}

persistence-modules/hibernate-mapping/src/main/java/com/baeldung/hibernate/wherejointable/UserGroupRole.java

@@ -0,0 +1,7 @@
+package com.baeldung.hibernate.wherejointable;
+
+public enum UserGroupRole {
+
+    MEMBER, MODERATOR
+
+}

persistence-modules/hibernate-mapping/src/test/java/com/baeldung/hibernate/wherejointable/HibernateWhereJoinTableIntegrationTest.java

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+package com.baeldung.hibernate.wherejointable;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.util.List;
+
+import org.hibernate.Session;
+import org.hibernate.SessionFactory;
+import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
+import org.hibernate.cfg.Configuration;
+import org.hibernate.dialect.H2Dialect;
+import org.hibernate.service.ServiceRegistry;
+import org.junit.After;
+import org.junit.AfterClass;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+public class HibernateWhereJoinTableIntegrationTest {
+
+    private static SessionFactory sessionFactory;
+
+    private Session session;
+
+    /**
+     * Test data
+     */
+    private User user1;
+    private User user2;
+    private User user3;
+    private Group group1;
+    private Group group2;
+
+    @BeforeClass
+    public static void beforeTests() {
+        Configuration configuration = new Configuration().addAnnotatedClass(User.class)
+            .addAnnotatedClass(Group.class)
+            .addAnnotatedClass(UserGroupRelation.class)
+            .setProperty("hibernate.dialect", H2Dialect.class.getName())
+            .setProperty("hibernate.connection.driver_class", org.h2.Driver.class.getName())
+            .setProperty("hibernate.connection.url", "jdbc:h2:mem:test")
+            .setProperty("hibernate.connection.username", "sa")
+            .setProperty("hibernate.connection.password", "")
+            .setProperty("hibernate.hbm2ddl.auto", "update");
+        
+        ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
+            .applySettings(configuration.getProperties())
+            .build();
+        
+        sessionFactory = configuration.buildSessionFactory(serviceRegistry);
+    }
+
+    @Before
+    public void setUp() {
+        session = sessionFactory.openSession();
+        session.beginTransaction();
+
+        user1 = new User("user1");
+        user2 = new User("user2");
+        user3 = new User("user3");
+
+        group1 = new Group("group1");
+        group2 = new Group("group2");
+
+        session.save(group1);
+        session.save(group2);
+
+        session.save(user1);
+        session.save(user2);
+        session.save(user3);
+
+        saveRelation(user1, group1, UserGroupRole.MODERATOR);
+        saveRelation(user2, group1, UserGroupRole.MODERATOR);
+        saveRelation(user3, group1, UserGroupRole.MEMBER);
+
+        saveRelation(user1, group2, UserGroupRole.MEMBER);
+        saveRelation(user2, group2, UserGroupRole.MODERATOR);
+    }
+
+    @After
+    public void tearDown() {
+        session.getTransaction().commit();
+        session.close();
+    }
+
+    @AfterClass
+    public static void afterTests() {
+        sessionFactory.close();
+    }
+
+    @Test
+    public void givenUser1_getGroups_returnsAllGroups() {
+        List<Group> groups = user1.getGroups();
+        assertEquals(2, groups.size());
+
+        assertTrue(groups.contains(group1));
+        assertTrue(groups.contains(group2));
+    }
+
+    @Test
+    public void givenUser1_getModeratorGroups_returnsOnlyModeratorGroups() {
+        List<Group> groups = user1.getModeratorGroups();
+        assertEquals(1, groups.size());
+
+        assertTrue(groups.contains(group1));
+    }
+
+    private void saveRelation(User user, Group group, UserGroupRole role) {
+        UserGroupRelation relation = new UserGroupRelation(user.getId(), group.getId(), role);
+
+        session.save(relation);
+        session.flush();
+        session.refresh(user);
+        session.refresh(group);
+    }
+
+}