BAEL-2043: An Intro to Hibernate Entity Lifecycle (#4960)

* "An Intro to Hibernate Entity Lifecycle"

"An Intro to Hibernate Entity Lifecycle"
by Rudi

* Revision from Predrag's feedback

* Another revision from Predrag's feedback

* Another feedback.

hibernate5/src/main/java/com/baeldung/hibernate/lifecycle/DirtyDataInspector.java

@@ -0,0 +1,26 @@
+package com.baeldung.hibernate.lifecycle;
+
+import org.hibernate.EmptyInterceptor;
+import org.hibernate.type.Type;
+
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.List;
+
+public class DirtyDataInspector extends EmptyInterceptor {
+    private static final ArrayList<FootballPlayer> dirtyEntities = new ArrayList<>();
+
+    @Override
+    public boolean onFlushDirty(Object entity, Serializable id, Object[] currentState, Object[] previousState, String[] propertyNames, Type[] types) {
+        dirtyEntities.add((FootballPlayer) entity);
+        return true;
+    }
+
+    public static List<FootballPlayer> getDirtyEntities() {
+        return dirtyEntities;
+    }
+
+    public static void clearDirtyEntitites() {
+        dirtyEntities.clear();
+    }
+}

hibernate5/src/main/java/com/baeldung/hibernate/lifecycle/FootballPlayer.java

@@ -0,0 +1,35 @@
+package com.baeldung.hibernate.lifecycle;
+
+import javax.persistence.*;
+
+@Entity
+@Table(name = "Football_Player")
+public class FootballPlayer {
+    @Id
+    @GeneratedValue
+    private long id;
+
+    @Column
+    private String 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;
+    }
+
+    @Override
+    public String toString() {
+        return "FootballPlayer{" + "id=" + id + ", name='" + name + '\'' + '}';
+    }
+}

hibernate5/src/main/java/com/baeldung/hibernate/lifecycle/HibernateLifecycleUtil.java

@@ -0,0 +1,96 @@
+package com.baeldung.hibernate.lifecycle;
+
+import org.h2.tools.RunScript;
+import org.hibernate.Session;
+import org.hibernate.SessionFactory;
+import org.hibernate.Transaction;
+import org.hibernate.boot.Metadata;
+import org.hibernate.boot.MetadataSources;
+import org.hibernate.boot.SessionFactoryBuilder;
+import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
+import org.hibernate.engine.spi.EntityEntry;
+import org.hibernate.engine.spi.SessionImplementor;
+import org.hibernate.service.ServiceRegistry;
+
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.net.URL;
+import java.sql.Connection;
+import java.sql.DriverManager;
+import java.sql.ResultSet;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.Properties;
+import java.util.stream.Collectors;
+
+public class HibernateLifecycleUtil {
+    private static SessionFactory sessionFactory;
+    private static Connection connection;
+
+    public static void init() throws Exception {
+        Properties hbConfigProp = getHibernateProperties();
+        Class.forName(hbConfigProp.getProperty("hibernate.connection.driver_class"));
+        connection = DriverManager.getConnection(hbConfigProp.getProperty("hibernate.connection.url"), hbConfigProp.getProperty("hibernate.connection.username"), hbConfigProp.getProperty("hibernate.connection.password"));
+
+        try (InputStream h2InitStream = Thread.currentThread().getContextClassLoader().getResourceAsStream("lifecycle-init.sql");
+            InputStreamReader h2InitReader = new InputStreamReader(h2InitStream)) {
+            RunScript.execute(connection, h2InitReader);
+        }
+
+        ServiceRegistry serviceRegistry = configureServiceRegistry();
+        sessionFactory = getSessionFactoryBuilder(serviceRegistry).applyInterceptor(new DirtyDataInspector()).build();
+    }
+
+    public static void tearDown() throws Exception {
+        sessionFactory.close();
+        connection.close();
+    }
+
+    public static SessionFactory getSessionFactory() {
+        return sessionFactory;
+    }
+
+    private static SessionFactoryBuilder getSessionFactoryBuilder(ServiceRegistry serviceRegistry) {
+        MetadataSources metadataSources = new MetadataSources(serviceRegistry);
+        metadataSources.addAnnotatedClass(FootballPlayer.class);
+
+        Metadata metadata = metadataSources.buildMetadata();
+        return metadata.getSessionFactoryBuilder();
+
+    }
+
+    private static ServiceRegistry configureServiceRegistry() throws IOException {
+        Properties properties = getHibernateProperties();
+        return new StandardServiceRegistryBuilder().applySettings(properties).build();
+    }
+
+    private static Properties getHibernateProperties() throws IOException {
+        Properties properties = new Properties();
+        URL propertiesURL = Thread.currentThread().getContextClassLoader().getResource("hibernate-lifecycle.properties");
+        try (FileInputStream inputStream = new FileInputStream(propertiesURL.getFile())) {
+            properties.load(inputStream);
+        }
+        return properties;
+    }
+
+    public static List<EntityEntry> getManagedEntities(Session session) {
+        Map.Entry<Object, EntityEntry>[] entries = ((SessionImplementor) session).getPersistenceContext().reentrantSafeEntityEntries();
+        return Arrays.stream(entries).map(e -> e.getValue()).collect(Collectors.toList());
+    }
+
+    public static Transaction startTransaction(Session s) {
+        Transaction tx = s.getTransaction();
+        tx.begin();
+        return tx;
+    }
+
+    public static int queryCount(String query) throws Exception {
+        try (ResultSet rs = connection.createStatement().executeQuery(query)) {
+            rs.next();
+            return rs.getInt(1);
+        }
+    }
+}

hibernate5/src/test/java/com/baeldung/hibernate/interceptors/HibernateInterceptorUnitTest.java

@@ -58,5 +58,4 @@ public class HibernateInterceptorUnitTest {
         transaction.commit();
         session.close();
     }
-    
 }

hibernate5/src/test/java/com/baeldung/hibernate/lifecycle/HibernateLifecycleUnitTest.java

@@ -0,0 +1,164 @@
+package com.baeldung.hibernate.lifecycle;
+
+import org.hibernate.Session;
+import org.hibernate.SessionFactory;
+import org.hibernate.Transaction;
+import org.hibernate.engine.spi.Status;
+import org.junit.AfterClass;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.util.List;
+
+import static com.baeldung.hibernate.lifecycle.DirtyDataInspector.getDirtyEntities;
+import static com.baeldung.hibernate.lifecycle.HibernateLifecycleUtil.*;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class HibernateLifecycleUnitTest {
+
+    @BeforeClass
+    public static void setup() throws Exception {
+        HibernateLifecycleUtil.init();
+
+    }
+
+    @AfterClass
+    public static void tearDown() throws Exception {
+        HibernateLifecycleUtil.tearDown();
+    }
+
+    @Before
+    public void beforeMethod() {
+        DirtyDataInspector.clearDirtyEntitites();
+    }
+
+    @Test
+    public void whenEntityLoaded_thenEntityManaged() throws Exception {
+        SessionFactory sessionFactory = HibernateLifecycleUtil.getSessionFactory();
+        try (Session session = sessionFactory.openSession()) {
+            Transaction transaction = startTransaction(session);
+
+            assertThat(getManagedEntities(session)).isEmpty();
+
+            List<FootballPlayer> players = session.createQuery("from FootballPlayer").getResultList();
+            assertThat(getManagedEntities(session)).size().isEqualTo(3);
+
+            assertThat(getDirtyEntities()).isEmpty();
+
+            FootballPlayer gigiBuffon = players.stream().filter(p -> p.getId() == 3).findFirst().get();
+
+            gigiBuffon.setName("Gianluigi Buffon");
+            transaction.commit();
+
+            assertThat(getDirtyEntities()).size().isEqualTo(1);
+            assertThat(getDirtyEntities().get(0).getId()).isEqualTo(3);
+            assertThat(getDirtyEntities().get(0).getName()).isEqualTo("Gianluigi Buffon");
+        }
+    }
+
+    @Test
+    public void whenDetached_thenNotTracked() throws Exception {
+        SessionFactory sessionFactory = HibernateLifecycleUtil.getSessionFactory();
+        try (Session session = sessionFactory.openSession()) {
+            Transaction transaction = startTransaction(session);
+
+            FootballPlayer cr7 = session.get(FootballPlayer.class, 1L);
+            assertThat(getManagedEntities(session)).size().isEqualTo(1);
+            assertThat(getManagedEntities(session).get(0).getId()).isEqualTo(cr7.getId());
+
+            session.evict(cr7);
+            assertThat(getManagedEntities(session)).size().isEqualTo(0);
+
+            cr7.setName("CR7");
+            transaction.commit();
+
+            assertThat(getDirtyEntities()).isEmpty();
+        }
+    }
+
+    @Test
+    public void whenReattached_thenTrackedAgain() throws Exception {
+        SessionFactory sessionFactory = HibernateLifecycleUtil.getSessionFactory();
+        try (Session session = sessionFactory.openSession()) {
+            Transaction transaction = startTransaction(session);
+
+            FootballPlayer messi = session.get(FootballPlayer.class, 2L);
+
+            session.evict(messi);
+            messi.setName("Leo Messi");
+            transaction.commit();
+            assertThat(getDirtyEntities()).isEmpty();
+
+            transaction = startTransaction(session);
+            session.update(messi);
+            transaction.commit();
+            assertThat(getDirtyEntities()).size().isEqualTo(1);
+            assertThat(getDirtyEntities().get(0).getName()).isEqualTo("Leo Messi");
+        }
+    }
+
+    @Test
+    public void givenNewEntityWithID_whenReattached_thenManaged() throws Exception {
+        SessionFactory sessionFactory = HibernateLifecycleUtil.getSessionFactory();
+        try (Session session = sessionFactory.openSession()) {
+            Transaction transaction = startTransaction(session);
+
+            FootballPlayer gigi = new FootballPlayer();
+            gigi.setId(3);
+            gigi.setName("Gigi the Legend");
+
+            session.update(gigi);
+            assertThat(getManagedEntities(session)).size().isEqualTo(1);
+
+            transaction.commit();
+            assertThat(getDirtyEntities()).size().isEqualTo(1);
+        }
+    }
+
+    @Test
+    public void givenTransientEntity_whenSave_thenManaged() throws Exception {
+        SessionFactory sessionFactory = HibernateLifecycleUtil.getSessionFactory();
+        try (Session session = sessionFactory.openSession()) {
+            Transaction transaction = startTransaction(session);
+
+            FootballPlayer neymar = new FootballPlayer();
+            neymar.setName("Neymar");
+
+            session.save(neymar);
+            assertThat(getManagedEntities(session)).size().isEqualTo(1);
+            assertThat(neymar.getId()).isNotNull();
+
+            int count = queryCount("select count(*) from Football_Player where name='Neymar'");
+            assertThat(count).isEqualTo(0);
+
+            transaction.commit();
+
+            count = queryCount("select count(*) from Football_Player where name='Neymar'");
+            assertThat(count).isEqualTo(1);
+
+            transaction = startTransaction(session);
+            session.delete(neymar);
+            transaction.commit();
+        }
+    }
+
+    @Test()
+    public void whenDelete_thenMarkDeleted() throws Exception {
+        SessionFactory sessionFactory = HibernateLifecycleUtil.getSessionFactory();
+        try (Session session = sessionFactory.openSession()) {
+            Transaction transaction = startTransaction(session);
+
+            FootballPlayer neymar = new FootballPlayer();
+            neymar.setName("Neymar");
+
+            session.save(neymar);
+            transaction.commit();
+
+            transaction = startTransaction(session);
+            session.delete(neymar);
+            assertThat(getManagedEntities(session).get(0).getStatus()).isEqualTo(Status.DELETED);
+            transaction.commit();
+        }
+    }
+}

hibernate5/src/test/resources/hibernate-lifecycle.properties

@@ -0,0 +1,9 @@
+hibernate.connection.driver_class=org.h2.Driver
+hibernate.connection.url=jdbc:h2:mem:lifecycledb;DB_CLOSE_DELAY=-1;
+hibernate.connection.username=sa
+hibernate.connection.password=
+hibernate.connection.autocommit=true
+
+hibernate.dialect=org.hibernate.dialect.H2Dialect
+hibernate.show_sql=true
+hibernate.hbm2ddl.auto=validate

hibernate5/src/test/resources/lifecycle-init.sql

@@ -0,0 +1,25 @@
+create sequence hibernate_sequence start with 1 increment by 1;
+
+create table Football_Player (
+  id bigint not null,
+  name varchar(255),
+  primary key (id)
+);
+
+insert into
+    Football_Player
+        (name, id)
+    values
+        ('Cristiano Ronaldo', next value for hibernate_sequence);
+
+insert into
+    Football_Player
+        (name, id)
+    values
+        ('Lionel Messi', next value for hibernate_sequence);
+
+insert into
+    Football_Player
+        (name, id)
+    values
+        ('Gigi Buffon', next value for hibernate_sequence);