第二百二十二节 JPA教程 - JPA合并示例

JPA教程 - JPA合并示例

在实体中合并后，我们可以更改其属性，EntityManager将自动更新数据库。

例子

下面的代码来自PersonDaoImpl.java。

package cn.w3cschool.common;import java.util.Date;import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;import org.springframework.transaction.annotation.Transactional;@Transactional
public class PersonDaoImpl {public void test() {Employee emp = new Employee();emp.setName("Tom");em.persist(emp);emp = em.find(Employee.class, emp.getId());Employee managedEmp = em.merge(emp);managedEmp.setLastAccessTime(new Date());}@PersistenceContextprivate EntityManager em;
}

以下代码来自Employee.java。

package cn.w3cschool.common;
import java.util.Date;import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;@Entity
public class Employee {@Idprivate int id;private String name;@Temporal(TemporalType.TIMESTAMP)private Date lastAccessTime;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 Date getLastAccessTime() {return lastAccessTime;}public void setLastAccessTime(Date lastAccessTime) {this.lastAccessTime = lastAccessTime;}public String toString() {return "Employee " + getId() + ": name: " + getName() +" lastAccessTime: " + getLastAccessTime();}
}

下载 Merge.zip

以下是数据库转储。

Table Name: EMPLOYEERow:Column Name: ID,Column Type: INTEGER:Column Value: 0Column Name: LASTACCESSTIME,Column Type: TIMESTAMP:Column Value: 2014-12-29 13:59:56.633Column Name: NAME,Column Type: VARCHAR:Column Value: Tom