[BAEL-4601] How to convert a Hibernate proxy to a real entity object

* Adds Domain Models
* Adds Integration Tests

persistence-modules/java-jpa-3/src/main/java/com/baeldung/jpa/hibernateunproxy/CreditCardPayment.java

@@ -0,0 +1,20 @@
+package com.baeldung.jpa.hibernateunproxy;
+
+import javax.persistence.Entity;
+import java.math.BigDecimal;
+
+@Entity
+public class CreditCardPayment extends Payment {
+
+    private String cardNumber;
+
+    CreditCardPayment(BigDecimal amount, WebUser webUser, String cardNumber) {
+        this.amount = amount;
+        this.webUser = webUser;
+        this.cardNumber = cardNumber;
+    }
+
+    protected CreditCardPayment() {
+    }
+
+}

persistence-modules/java-jpa-3/src/main/java/com/baeldung/jpa/hibernateunproxy/Payment.java

@@ -0,0 +1,47 @@
+package com.baeldung.jpa.hibernateunproxy;
+
+import javax.persistence.Entity;
+import javax.persistence.FetchType;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+import javax.persistence.Inheritance;
+import javax.persistence.InheritanceType;
+import javax.persistence.ManyToOne;
+import java.math.BigDecimal;
+import java.util.Objects;
+
+@Entity
+@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
+public abstract class Payment {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.AUTO)
+    private Long id;
+
+    @ManyToOne(fetch = FetchType.LAZY)
+    protected WebUser webUser;
+
+    protected BigDecimal amount;
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o)
+            return true;
+        if (o == null || getClass() != o.getClass())
+            return false;
+
+        Payment payment = (Payment) o;
+
+        return Objects.equals(id, payment.id);
+    }
+
+    @Override
+    public int hashCode() {
+        return id != null ? id.hashCode() : 0;
+    }
+
+    protected Payment() {
+    }
+
+}

persistence-modules/java-jpa-3/src/main/java/com/baeldung/jpa/hibernateunproxy/PaymentReceipt.java

@@ -0,0 +1,53 @@
+package com.baeldung.jpa.hibernateunproxy;
+
+import javax.persistence.Entity;
+import javax.persistence.FetchType;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+import javax.persistence.OneToOne;
+import java.util.Objects;
+import java.util.UUID;
+
+@Entity
+public class PaymentReceipt {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.AUTO)
+    private Long id;
+
+    @OneToOne(fetch = FetchType.LAZY)
+    private Payment payment;
+
+    private String transactionNumber;
+
+    PaymentReceipt(Payment payment) {
+        this.payment = payment;
+        this.transactionNumber = UUID.randomUUID().toString();
+    }
+
+    public Payment getPayment() {
+        return payment;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o)
+            return true;
+        if (o == null || getClass() != o.getClass())
+            return false;
+
+        PaymentReceipt that = (PaymentReceipt) o;
+
+        return Objects.equals(id, that.id);
+    }
+
+    @Override
+    public int hashCode() {
+        return id != null ? id.hashCode() : 0;
+    }
+
+    protected PaymentReceipt() {
+    }
+
+}

persistence-modules/java-jpa-3/src/main/java/com/baeldung/jpa/hibernateunproxy/WebUser.java

@@ -0,0 +1,42 @@
+package com.baeldung.jpa.hibernateunproxy;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+import java.util.Objects;
+
+@Entity
+public class WebUser {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.AUTO)
+    private Long id;
+
+    private String name;
+
+    WebUser(String name) {
+        this.name = name;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o)
+            return true;
+        if (o == null || getClass() != o.getClass())
+            return false;
+
+        WebUser webUser = (WebUser) o;
+
+        return Objects.equals(id, webUser.id);
+    }
+
+    @Override
+    public int hashCode() {
+        return id != null ? id.hashCode() : 0;
+    }
+
+    protected WebUser() {
+    }
+
+}

persistence-modules/java-jpa-3/src/main/resources/META-INF/persistence.xml

@@ -77,4 +77,24 @@
             <property name="hibernate.temp.use_jdbc_metadata_defaults" value="false"/>
         </properties>
     </persistence-unit>
+    <persistence-unit name="jpa-h2-hibernate-unproxy">
+        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
+        <class>com.baeldung.jpa.hibernateunproxy.Payment</class>
+        <class>com.baeldung.jpa.hibernateunproxy.CreditCardPayment</class>
+        <class>com.baeldung.jpa.hibernateunproxy.PaymentReceipt</class>
+        <class>com.baeldung.jpa.hibernateunproxy.WebUser</class>
+        <exclude-unlisted-classes>true</exclude-unlisted-classes>
+        <properties>
+            <property name="javax.persistence.jdbc.driver" value="org.h2.Driver"/>
+            <property name="javax.persistence.jdbc.url" value="jdbc:h2:mem:test"/>
+            <property name="javax.persistence.jdbc.user" value="sa"/>
+            <property name="javax.persistence.jdbc.password" value=""/>
+            <property name="javax.persistence.jdbc.driver" value="org.h2.Driver"/>
+            <property name="hibernate.dialect" value="org.hibernate.dialect.H2Dialect"/>
+            <property name="hibernate.hbm2ddl.auto" value="create-drop"/>
+            <property name="hibernate.show_sql" value="true"/>
+            <property name="hibernate.format_sql" value="true"/>
+            <property name="hibernate.temp.use_jdbc_metadata_defaults" value="false"/>
+        </properties>
+    </persistence-unit>
 </persistence>

persistence-modules/java-jpa-3/src/test/java/com/baeldung/jpa/hibernateunproxy/HibernateProxyIntegrationTest.java

@@ -0,0 +1,75 @@
+package com.baeldung.jpa.hibernateunproxy;
+
+import org.hibernate.Hibernate;
+import org.hibernate.proxy.HibernateProxy;
+import org.junit.Assert;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import javax.persistence.EntityManager;
+import javax.persistence.EntityManagerFactory;
+import javax.persistence.Persistence;
+import java.math.BigDecimal;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+public class HibernateProxyIntegrationTest {
+
+    private static EntityManager entityManager;
+
+    @BeforeAll
+    public static void setup() {
+        EntityManagerFactory factory = Persistence.createEntityManagerFactory("jpa-h2-hibernate-unproxy");
+        entityManager = factory.createEntityManager();
+        populateH2DB();
+    }
+
+    @Test
+    public void givenPaymentReceipt_whenAccessingPayment_thenVerifyType() {
+        PaymentReceipt paymentReceipt = entityManager.find(PaymentReceipt.class, 3L);
+        Assert.assertEquals(true, paymentReceipt.getPayment() instanceof HibernateProxy);
+    }
+
+    @Test
+    public void givenWebUserProxy_whenCreatingPayment_thenExecuteSingleStatement() {
+        entityManager.getTransaction().begin();
+
+        WebUser webUser = entityManager.getReference(WebUser.class, 1L);
+        Payment payment = new CreditCardPayment(new BigDecimal(100), webUser, "CN-1234");
+        entityManager.persist(payment);
+
+        entityManager.getTransaction().commit();
+        Assert.assertEquals(true, webUser instanceof HibernateProxy);
+    }
+
+    @Test
+    public void givenPaymentReceipt_whenCastingPaymentToConcreteClass_thenThrowClassCastException() {
+        PaymentReceipt paymentReceipt = entityManager.find(PaymentReceipt.class, 3L);
+        assertThrows(ClassCastException.class, () -> {
+            CreditCardPayment creditCardPayment = (CreditCardPayment) paymentReceipt.getPayment();
+        });
+    }
+
+    @Test
+    public void givenPaymentReceipt_whenPaymentIsUnproxied_thenReturnRealEntityObject() {
+        PaymentReceipt paymentReceipt = entityManager.find(PaymentReceipt.class, 3L);
+        Assert.assertEquals(true, Hibernate.unproxy(paymentReceipt.getPayment()) instanceof CreditCardPayment);
+    }
+
+    private static void populateH2DB() {
+        entityManager.getTransaction().begin();
+
+        WebUser webUser = new WebUser("name");
+        entityManager.persist(webUser);
+
+        Payment payment = new CreditCardPayment(new BigDecimal(100), webUser, "CN-1234");
+        entityManager.persist(payment);
+
+        PaymentReceipt receipt = new PaymentReceipt(payment);
+        entityManager.persist(receipt);
+
+        entityManager.getTransaction().commit();
+        entityManager.clear();
+    }
+
+}