BAEL-5763: Fix the HibernateException: Illegal attempt to associate a collection with two open sessions

Author: azhwani

persistence-modules/hibernate-exceptions-2/src/main/java/com/baeldung/hibernate/hibernateexception/Author.java

@@ -0,0 +1,45 @@
+package com.baeldung.hibernate.hibernateexception;
+
+import java.util.List;
+
+import jakarta.persistence.CascadeType;
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.OneToMany;
+
+@Entity
+public class Author {
+
+    @Id
+    private Long id;
+
+    private String name;
+
+    @OneToMany(mappedBy = "author", cascade = CascadeType.ALL)
+    private List<Book> books;
+
+    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<Book> getBooks() {
+        return books;
+    }
+
+    public void setBooks(List<Book> books) {
+        this.books = books;
+    }
+
+}

persistence-modules/hibernate-exceptions-2/src/main/java/com/baeldung/hibernate/hibernateexception/Book.java

@@ -0,0 +1,42 @@
+package com.baeldung.hibernate.hibernateexception;
+
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.ManyToOne;
+
+@Entity
+public class Book {
+
+    @Id
+    private Long id;
+
+    private String title;
+
+    @ManyToOne
+    private Author author;
+
+    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 Author getAuthor() {
+        return author;
+    }
+
+    public void setAuthor(Author author) {
+        this.author = author;
+    }
+
+}

persistence-modules/hibernate-exceptions-2/src/main/java/com/baeldung/hibernate/hibernateexception/HibernateUtil.java

@@ -0,0 +1,39 @@
+package com.baeldung.hibernate.hibernateexception;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.hibernate.SessionFactory;
+import org.hibernate.boot.Metadata;
+import org.hibernate.boot.MetadataSources;
+import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
+import org.hibernate.service.ServiceRegistry;
+
+public class HibernateUtil {
+    private static SessionFactory sessionFactory;
+
+    public static SessionFactory getSessionFactory() {
+        if (sessionFactory == null) {
+            Map<String, Object> settings = new HashMap<>();
+            settings.put("hibernate.connection.driver_class", "org.h2.Driver");
+            settings.put("hibernate.connection.url", "jdbc:h2:mem:test");
+            settings.put("hibernate.connection.username", "sa");
+            settings.put("hibernate.connection.password", "");
+            settings.put("hibernate.dialect", "org.hibernate.dialect.H2Dialect");
+            settings.put("hibernate.show_sql", "true");
+            settings.put("hibernate.hbm2ddl.auto", "create-drop");
+
+            ServiceRegistry standardRegistry = new StandardServiceRegistryBuilder().applySettings(settings)
+                .build();
+
+            Metadata metadata = new MetadataSources(standardRegistry).addAnnotatedClasses(Author.class, Book.class)
+                .getMetadataBuilder()
+                .build();
+
+            sessionFactory = metadata.getSessionFactoryBuilder()
+                .build();
+        }
+
+        return sessionFactory;
+    }
+}

persistence-modules/hibernate-exceptions-2/src/test/java/com/baeldung/hibernate/hibernateexception/HibernateExceptionUnitTest.java

@@ -0,0 +1,100 @@
+package com.baeldung.hibernate.hibernateexception;
+
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+import java.util.ArrayList;
+
+import org.hibernate.HibernateException;
+import org.hibernate.Session;
+import org.junit.jupiter.api.Test;
+
+class HibernateExceptionUnitTest {
+
+    @Test
+    void whenUsingOneHibernateSession_thenCorrect() {
+        try (Session session1 = HibernateUtil.getSessionFactory()
+            .openSession()) {
+            session1.beginTransaction();
+
+            Author author = new Author();
+            author.setId(2L);
+            author.setName("Jane Austen");
+            author.setBooks(new ArrayList<Book>());
+            session1.persist(author);
+
+            Author persistedAuthor = session1.get(Author.class, 2L);
+
+            Book newBook = new Book();
+            newBook.setId(1L);
+            newBook.setTitle("Pride and Prejudice");
+            persistedAuthor.getBooks()
+                .add(newBook);
+            session1.update(persistedAuthor);
+
+            session1.getTransaction()
+                .commit();
+        }
+    }
+
+    @Test
+    void whenUsingMoreThanOneHibernateSessionWithMergeMethod_thenCorrect() {
+        try (Session session1 = HibernateUtil.getSessionFactory()
+            .openSession();
+            Session session2 = HibernateUtil.getSessionFactory()
+                .openSession()) {
+            session1.beginTransaction();
+
+            Author author = new Author();
+            author.setId(3L);
+            author.setName("Leo Tolstoy");
+            author.setBooks(new ArrayList<Book>());
+            session1.persist(author);
+            Author persistedAuthor = session1.get(Author.class, 3L);
+            session1.getTransaction()
+                .commit();
+
+            session2.beginTransaction();
+            Book newBook = new Book();
+            newBook.setId(1L);
+            newBook.setTitle("War and Peace");
+            persistedAuthor.getBooks()
+                .add(newBook);
+            session2.merge(persistedAuthor);
+            session2.getTransaction()
+                .commit();
+        }
+    }
+
+    @Test
+    void whenUsingMoreThanOneHibernateSession_thenThrowHibernateException() {
+        assertThatThrownBy(() -> {
+            try (Session session1 = HibernateUtil.getSessionFactory()
+                .openSession();
+                Session session2 = HibernateUtil.getSessionFactory()
+                    .openSession()) {
+                session1.beginTransaction();
+
+                Author author = new Author();
+                author.setId(1L);
+                author.setName("Leo Tolstoy");
+                author.setBooks(new ArrayList<Book>());
+                session1.persist(author);
+                Author persistedAuthor = session1.get(Author.class, 1L);
+                session1.getTransaction()
+                    .commit();
+
+                session2.beginTransaction();
+                Book newBook = new Book();
+                newBook.setId(1L);
+                newBook.setTitle("War and Peace");
+                persistedAuthor.getBooks()
+                    .add(newBook);
+                session2.update(persistedAuthor);
+                session2.getTransaction()
+                    .commit();
+            }
+        }).isInstanceOf(HibernateException.class)
+            .hasMessageContaining("Illegal attempt to associate a collection with two open sessions");
+    }
+
+}