BAEL-5440: hql distinct queries (#12007)

* BAEL-5440: hql distinct queries

* BAEL-5440: formated the code and renamed test class

persistence-modules/hibernate-queries/src/main/java/com/baeldung/hibernate/HibernateUtil.java

@@ -13,6 +13,8 @@ import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
 import org.hibernate.service.ServiceRegistry;
 
 import com.baeldung.hibernate.customtypes.LocalDateStringType;
+import com.baeldung.hibernate.distinct.entities.Post;
+import com.baeldung.hibernate.distinct.entities.Comment;
 import com.baeldung.hibernate.entities.DeptEmployee;
 import com.baeldung.hibernate.pojo.Student;
 
@@ -41,6 +43,8 @@ public class HibernateUtil {
         metadataSources.addAnnotatedClass(Student.class);
         metadataSources.addAnnotatedClass(DeptEmployee.class);
         metadataSources.addAnnotatedClass(com.baeldung.hibernate.entities.Department.class);
+        metadataSources.addAnnotatedClass(Comment.class);
+        metadataSources.addAnnotatedClass(Post.class);
 
         Metadata metadata = metadataSources.getMetadataBuilder()
                 .applyBasicType(LocalDateStringType.INSTANCE)

persistence-modules/hibernate-queries/src/main/java/com/baeldung/hibernate/distinct/entities/Comment.java

@@ -0,0 +1,28 @@
+package com.baeldung.hibernate.distinct.entities;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+
+@Entity
+public class Comment {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private long id;
+
+    private String text;
+
+    public Comment() {
+    }
+
+    public Comment(String text) {
+        this.text = text;
+    }
+
+    @Override
+    public String toString() {
+        return "Comment{" + "id=" + id + ", text='" + text + '\'' + '}';
+    }
+}

persistence-modules/hibernate-queries/src/main/java/com/baeldung/hibernate/distinct/entities/Post.java

@@ -0,0 +1,59 @@
+package com.baeldung.hibernate.distinct.entities;
+
+import java.util.List;
+
+import javax.persistence.Entity;
+import javax.persistence.FetchType;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+import javax.persistence.OneToMany;
+
+import org.hibernate.annotations.Cascade;
+import org.hibernate.annotations.CascadeType;
+
+@Entity
+public class Post {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private long id;
+
+    private String title;
+
+    @OneToMany
+    @Cascade(CascadeType.ALL)
+    private List<Comment> comments;
+
+    public Post() {
+    }
+
+    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;
+    }
+
+    public List<Comment> getComments() {
+        return comments;
+    }
+
+    public void setComments(List<Comment> comments) {
+        this.comments = comments;
+    }
+
+    @Override
+    public String toString() {
+        return "Post{" + "id=" + id + ", title='" + title + '\'' + ", comments=" + comments + '}';
+    }
+}

persistence-modules/hibernate-queries/src/test/java/com/baeldung/hibernate/distinct/entities/DistinctHqlQueriesUnitTest.java

@@ -0,0 +1,80 @@
+package com.baeldung.hibernate.distinct.entities;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.List;
+
+import org.hibernate.Session;
+import org.hibernate.Transaction;
+import org.hibernate.annotations.QueryHints;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import com.baeldung.hibernate.HibernateUtil;
+
+public class DistinctHqlQueriesUnitTest {
+
+    private Session session;
+
+    @Before
+    public void setUp() throws IOException {
+        this.session = HibernateUtil.getSessionFactory()
+            .openSession();
+        saveDummyData();
+    }
+
+    private void saveDummyData() {
+        Transaction trx = session.beginTransaction();
+        session.createQuery("delete from Post")
+            .executeUpdate();
+
+        Post post = new Post();
+        post.setTitle("Distinct Queries in HQL");
+        post.setComments(Arrays.asList(new Comment("Great article!"), new Comment("Nice one :)"), new Comment("Keep up the good work!")));
+        session.persist(post);
+
+        trx.commit();
+    }
+
+    @After
+    public void tearDown() {
+        session.close();
+    }
+
+    @Test
+    public void whenExecutingSelectQuery_thereWillBeDuplicates() {
+        String hql = "SELECT p FROM Post p LEFT JOIN FETCH p.comments";
+        List<Post> posts = session.createQuery(hql, Post.class)
+            .getResultList();
+
+        assertThat(posts).hasSize(3);
+    }
+
+    @Test
+    public void whenExecutingSelectDistinctQuery_thereShouldBeNoDuplicates() {
+        String hql = "SELECT DISTINCT p FROM Post p LEFT JOIN FETCH p.comments";
+        List<Post> posts = session.createQuery(hql, Post.class)
+            .getResultList();
+
+        assertThat(posts).hasSize(1)
+            .allMatch(post -> post.getTitle()
+                .equals("Distinct Queries in HQL") && post.getComments()
+                .size() == 3);
+    }
+
+    @Test
+    public void whenExecutingSelectDistinctQueryWithHint_thereShouldBeNoDuplicates() {
+        String hql = "SELECT DISTINCT p FROM Post p LEFT JOIN FETCH p.comments";
+        List<Post> posts = session.createQuery(hql, Post.class)
+            .setHint(QueryHints.PASS_DISTINCT_THROUGH, false)
+            .getResultList();
+
+        assertThat(posts).hasSize(1)
+            .allMatch(post -> post.getTitle()
+                .equals("Distinct Queries in HQL") && post.getComments()
+                .size() == 3);
+    }
+}