惠州什么是JPA一对一映射级联？_北大青鸟IT学校

什么是JPA一对一映射级联？这是大家在学习Java的过程都会遇到的问题，那么下面我们一起来看看惠州北大青鸟学术部老师是怎么讲解这道题的。

以下代码显示如何为一对一映射设置级联操作。

 @OneToOne(cascade=CascadeType.ALL,mappedBy="department")  private Person person;

实例

下面的代码来自Department.java。

package cn.w3cschool.common;

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

@Entitypublic class Department {
 @Id
 @GeneratedValue(strategy=GenerationType.IDENTITY)  private long id;  
 private String name;
 
 @OneToOne(cascade=CascadeType.ALL,mappedBy="department")  private Person person;  
 public Person getPerson() {
   return person;
 }  public void setPerson(Person person) {
   this.person = person;
 }  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;
 }

 @Override  public String toString() {
   return "Department [id=" + id + ", name=" + name + ", person=" + person
       + "]";
 }
}

下面的代码来自PersonDaoImpl.java。

package cn.w3cschool.common;


import java.util.List;

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

import org.springframework.transaction.annotation.Transactional;

@Transactionalpublic class PersonDaoImpl {  public void test(){
   Person p1 = new Person("Tom");
   
   p1.setName("Tom");
   
   Department d = new Department();
   d.setName("Design");
   p1.setDepartment(d);
   d.setPerson(p1);
   
   em.persist(p1);
   em.persist(d);
   
   Query query = em.createQuery("SELECT e FROM Person e");
   List<Person> list = (List<Person>) query.getResultList();
   System.out.println(list.get(0).getDepartment());
   
   em.remove(list.get(0));
   
 }
 @PersistenceContext  private EntityManager em;
}

下面的代码来自Person.java。

package cn.w3cschool.common;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;
@Entitypublic class Person {
 @Id
 @GeneratedValue(strategy=GenerationType.IDENTITY)  private long id;  
 private String name;
 
 @OneToOne(cascade=CascadeType.ALL)
 @JoinColumn(name="DEPT_ID")  
 private Department department;  
 public Person() {}  public Person(String name) {
   this.name = name;
 }  public Department getDepartment() {
   return department;
 }  public void setDepartment(Department department) {
   this.department = department;
 }  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;
 }

 @Override  public String toString() {
   return "Person [id=" + id + ", name=" + name + "]";
 }

}

通过老师的讲解，你知道什么是JPA一对一映射级联了吗？想了解更多关于Java的知识，联系在线客服，或者来惠州北大青鸟新方舟校区了解一下。

Java

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