JPA ID生成策略示例

JPA教程 – JPA ID生成策略示例

当使用id字段的自动生成值时，我们可以选择生成策略。我们使用的一个常见策略是IDENTITY。

例子

以下代码来自Professor.java。

package cn.w3cschool.common;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Professor {
  @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
  private int id;
  private String name;
  private long salary;

  public int getId() {
    return id;
  }

  public void setId(int id) {
    this.id = id;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public long getSalary() {
    return salary;
  }

  public void setSalary(long salary) {
    this.salary = salary;
  }

  public String toString() {
    return "Employee id: " + getId() + " name: " + getName() + " salary: "
        + getSalary();
  }
}

以下代码来自App.java。

package cn.w3cschool.common;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class App {

  public static void main(String[] args) {
    ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(
        "applicationContext.xml");
    PersonDaoImpl dao = (PersonDaoImpl) context.getBean("personDao");

    dao.test();

    context.close();

    Helper.checkData();
  }
}

下面的代码来自PersonDaoImpl.java。

package cn.w3cschool.common;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

import org.springframework.transaction.annotation.Transactional;

@Transactional
public class PersonDaoImpl {
  public void test() {

    Professor emp = new Professor();

    emp.setName("name");
    emp.setSalary(12345);
    em.persist(emp);

  }

  @PersistenceContext
  private EntityManager em;
}

下载 ID_GenerationType.IDENTITY.zip

这里是数据库表转储。

Table Name: PROFESSOR
 Row:
    Column Name: ID,
    Column Type: INTEGER:
    Column Value: 1

    Column Name: NAME,
    Column Type: VARCHAR:
    Column Value: name

    Column Name: SALARY,
    Column Type: BIGINT:
    Column Value: 12345