ID Generation (Table)

There are four identifier generation strategies (AUTO, IDENTITY, SEQUENCE and TABLE). Marking a field with the @GeneratedValue annotation specifies that a value will be automatically generated for that field.

Employee.java

package org.metadata.jee.jpa.entities; import java.io.Serializable; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.Table; import javax.persistence.TableGenerator; @Entity @Table(name = "EMP_TBL") @TableGenerator(name = "EMP_GENTOR", table = "ID_GEN", pkColumnName = "GEN_NAME", valueColumnName = "GEN_VAL", pkColumnValue = "EMP_GEN", allocationSize = 10) public class Employee implements Serializable {       @Id       @GeneratedValue(strategy = GenerationType.TABLE, generator = "EMP_GENTOR")       private long id;       @Column(name = "EMP_NAME")       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;       } }

EmployeeTest.java

package org.metadata.jee.jpa.entities; import javax.persistence.EntityManager; import javax.persistence.EntityManagerFactory; import javax.persistence.Persistence; public class EmployeeTest {       private EntityManagerFactory emf;       public EmployeeTest() {             emf = Persistence.createEntityManagerFactory("METADATA_JPA");       }       public String insert() {             EntityManager em = emf.createEntityManager();             // Begin Transaction             em.getTransaction().begin();             Employee employee = new Employee();             employee.setName("Mr Jone");             // Insert employee to database             em.persist(employee);             // Commit Transaction             em.getTransaction().commit();             return "OK";       }       public static void main(String[] args) {             EmployeeTest employeeTest = new EmployeeTest();             String status = employeeTest.insert();             if (status.equals("OK")) {                   System.out.println("Insert Employee test is success.");             }       } }

persistence.xml

<?xml version="1.0" encoding="UTF-8"?> <persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence"       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"       xsi:schemaLocation="http://java.sun.com/xml/ns/persistence       http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">   <persistence-unit name="METADATA_JPA" transaction-type="RESOURCE_LOCAL">     <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>       <class>org.metadata.jee.jpa.entities.Employee</class>     <properties>       <property name="javax.persistence.jdbc.url"           value="jdbc:mysql://localhost:3306/metadatajpa"/>       <property name="javax.persistence.jdbc.user" value="metadatajpa"/>         <property name="javax.persistence.jdbc.password" value="metadatajpa"/>       <property name="javax.persistence.jdbc.driver"       value="com.mysql.jdbc.Driver"/>          </properties>   </persistence-unit> </persistence>

create.sql

CREATE TABLE EMP_TBL (       ID BIGINT NOT NULL,       EMP_NAME VARCHAR(255), PRIMARY KEY (ID) ); CREATE TABLE ID_GEN (GEN_NAME VARCHAR(50) NOT NULL, GEN_VAL DECIMAL(38), PRIMARY KEY (GEN_NAME)); INSERT INTO ID_GEN(GEN_NAME, GEN_VAL) values ('EMP_GEN', 0);