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;
+    }
+
+}