BAEL-2901 Composite primary keys in JPA (#6994)

* BAEL-2901 Composite primary keys in JPA

* Formatted code using the recommended formatter.xml

persistence-modules/java-jpa/src/main/java/com/baeldung/jpa/entity/Account.java

@@ -0,0 +1,43 @@
+package com.baeldung.jpa.entity;
+
+import javax.persistence.Entity;
+import javax.persistence.Id;
+import javax.persistence.IdClass;
+
+@Entity
+@IdClass(AccountId.class)
+public class Account {
+
+    @Id
+    private String accountNumber;
+
+    @Id
+    private String accountType;
+
+    private String description;
+
+    public String getAccountNumber() {
+        return accountNumber;
+    }
+
+    public void setAccountNumber(String accountNumber) {
+        this.accountNumber = accountNumber;
+    }
+
+    public String getAccountType() {
+        return accountType;
+    }
+
+    public void setAccountType(String accountType) {
+        this.accountType = accountType;
+    }
+
+    public String getDescription() {
+        return description;
+    }
+
+    public void setDescription(String description) {
+        this.description = description;
+    }
+
+}

persistence-modules/java-jpa/src/main/java/com/baeldung/jpa/entity/AccountId.java

@@ -0,0 +1,52 @@
+package com.baeldung.jpa.entity;
+
+import java.io.Serializable;
+
+public class AccountId implements Serializable {
+
+    private static final long serialVersionUID = 1L;
+
+    private String accountNumber;
+    private String accountType;
+
+    public AccountId() {
+
+    }
+
+    public AccountId(String accountNumber, String accountType) {
+        this.accountNumber = accountNumber;
+        this.accountType = accountType;
+    }
+
+    @Override
+    public int hashCode() {
+        final int prime = 31;
+        int result = 1;
+        result = prime * result + ((accountNumber == null) ? 0 : accountNumber.hashCode());
+        result = prime * result + ((accountType == null) ? 0 : accountType.hashCode());
+        return result;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj)
+            return true;
+        if (obj == null)
+            return false;
+        if (getClass() != obj.getClass())
+            return false;
+        AccountId other = (AccountId) obj;
+        if (accountNumber == null) {
+            if (other.accountNumber != null)
+                return false;
+        } else if (!accountNumber.equals(other.accountNumber))
+            return false;
+        if (accountType == null) {
+            if (other.accountType != null)
+                return false;
+        } else if (!accountType.equals(other.accountType))
+            return false;
+        return true;
+    }
+
+}

persistence-modules/java-jpa/src/main/java/com/baeldung/jpa/entity/Book.java

@@ -0,0 +1,34 @@
+package com.baeldung.jpa.entity;
+
+import javax.persistence.EmbeddedId;
+import javax.persistence.Entity;
+
+@Entity
+public class Book {
+
+    @EmbeddedId
+    private BookId bookId;
+
+    private String description;
+
+    public Book() {
+
+    }
+
+    public Book(BookId bookId) {
+        this.bookId = bookId;
+    }
+
+    public BookId getBookId() {
+        return bookId;
+    }
+
+    public String getDescription() {
+        return description;
+    }
+
+    public void setDescription(String description) {
+        this.description = description;
+    }
+
+}

persistence-modules/java-jpa/src/main/java/com/baeldung/jpa/entity/BookId.java

@@ -0,0 +1,62 @@
+package com.baeldung.jpa.entity;
+
+import java.io.Serializable;
+
+import javax.persistence.Embeddable;
+
+@Embeddable
+public class BookId implements Serializable {
+
+    private static final long serialVersionUID = 1L;
+    private String title;
+    private String language;
+
+    public BookId() {
+
+    }
+
+    public BookId(String title, String language) {
+        this.title = title;
+        this.language = language;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public String getLanguage() {
+        return language;
+    }
+
+    @Override
+    public int hashCode() {
+        final int prime = 31;
+        int result = 1;
+        result = prime * result + ((language == null) ? 0 : language.hashCode());
+        result = prime * result + ((title == null) ? 0 : title.hashCode());
+        return result;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj)
+            return true;
+        if (obj == null)
+            return false;
+        if (getClass() != obj.getClass())
+            return false;
+        BookId other = (BookId) obj;
+        if (language == null) {
+            if (other.language != null)
+                return false;
+        } else if (!language.equals(other.language))
+            return false;
+        if (title == null) {
+            if (other.title != null)
+                return false;
+        } else if (!title.equals(other.title))
+            return false;
+        return true;
+    }
+
+}

persistence-modules/java-jpa/src/test/java/com/baeldung/jpa/entity/CompositeKeysIntegrationTest.java

@@ -0,0 +1,114 @@
+package com.baeldung.jpa.entity;
+
+import static org.junit.Assert.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import javax.persistence.EntityManager;
+import javax.persistence.EntityManagerFactory;
+import javax.persistence.Persistence;
+
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+public class CompositeKeysIntegrationTest {
+
+    private static final String SAVINGS_ACCOUNT = "Savings";
+    private static final String ACCOUNT_NUMBER = "JXSDF324234";
+    private static final String ENGLISH = "English";
+    private static final String WAR_AND_PEACE = "War and Peace";
+
+    private static EntityManagerFactory emf;
+    private static EntityManager em;
+
+    @BeforeClass
+    public static void setup() {
+        emf = Persistence.createEntityManagerFactory("jpa-entity-definition");
+        em = emf.createEntityManager();
+    }
+
+    @Test
+    public void persistBookWithCompositeKeyThenRetrieveDetails() {
+        Book warAndPeace = createBook();
+        persist(warAndPeace);
+        clearThePersistenceContext();
+        Book book = findBookByBookId();
+        verifyAssertionsWith(book);
+    }
+
+    @Test
+    public void persistAccountWithCompositeKeyThenRetrieveDetails() {
+        Account savingsAccount = createAccount();
+        persist(savingsAccount);
+        clearThePersistenceContext();
+        Account account = findAccountByAccountId();
+        verifyAssertionsWith(account);
+    }
+
+    @AfterClass
+    public static void destroy() {
+        if (em != null) {
+            em.close();
+        }
+        if (emf != null) {
+            emf.close();
+        }
+    }
+
+    private Account createAccount() {
+        Account savingsAccount = new Account();
+        savingsAccount.setAccountNumber(ACCOUNT_NUMBER);
+        savingsAccount.setAccountType(SAVINGS_ACCOUNT);
+        savingsAccount.setDescription("Savings account");
+        return savingsAccount;
+    }
+
+    private void verifyAssertionsWith(Account account) {
+        assertEquals(ACCOUNT_NUMBER, account.getAccountNumber());
+        assertEquals(SAVINGS_ACCOUNT, account.getAccountType());
+    }
+
+    private Account findAccountByAccountId() {
+        return em.find(Account.class, new AccountId(ACCOUNT_NUMBER, SAVINGS_ACCOUNT));
+    }
+
+    private void persist(Account account) {
+        em.getTransaction()
+            .begin();
+        em.persist(account);
+        em.getTransaction()
+            .commit();
+    }
+
+    private Book findBookByBookId() {
+        return em.find(Book.class, new BookId(WAR_AND_PEACE, ENGLISH));
+    }
+
+    private Book createBook() {
+        BookId bookId = new BookId(WAR_AND_PEACE, ENGLISH);
+        Book warAndPeace = new Book(bookId);
+        warAndPeace.setDescription("Novel and Historical Fiction");
+        return warAndPeace;
+    }
+
+    private void verifyAssertionsWith(Book book) {
+        assertNotNull(book);
+        assertNotNull(book.getBookId());
+        assertEquals(WAR_AND_PEACE, book.getBookId()
+            .getTitle());
+        assertEquals(ENGLISH, book.getBookId()
+            .getLanguage());
+    }
+
+    private void persist(Book book) {
+        em.getTransaction()
+            .begin();
+        em.persist(book);
+        em.getTransaction()
+            .commit();
+    }
+
+    private void clearThePersistenceContext() {
+        em.clear();
+    }
+}