惠州Java中JPA持久关系级联是什么？_北大青鸟IT学校

Java中JPA持久关系级联是什么？相信这是每个学习Java的同学都会遇到的问题，下面我们一起来看看惠州北大青鸟老师是怎么回答的。

以下代码显示级联持久操作。

实例

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;

@Transactionalpublic class PersonDaoImpl {  public void test() {
   Employee emp = new Employee();
   emp.setName("Tom");
   emp.setId(1);

   Address addr = new Address();
   addr.setId(1);
   addr.setStreet("street");
   addr.setCity("city");
   addr.setState("state");
   emp.setAddress(addr);
   em.persist(emp);

 }

 @PersistenceContext  private EntityManager em;
}

以下代码来自Employee.java。

package cn.w3cschool.common;


import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToOne;

@Entitypublic class Employee {
   @Id    private int id;    private String name;
   
   @ManyToOne(cascade=CascadeType.PERSIST)
   Address address;    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 Address getAddress() {
       return address;
   }    
   public void setAddress(Address address) {
       this.address = address;
   }    public String toString() {
       return "Employee id: " + getId() + " name: " + getName() +               " with " + getAddress();
   }
}

以下代码来自Address.java。

package cn.w3cschool.common;


import javax.persistence.Entity;
import javax.persistence.Id;

@Entitypublic class Address {
   @Id    private int id;    private String street;    private String city;    private String state;    private String zip;    
   public int getId() {
       return id;
   }    
   public void setId(int id) {
       this.id = id;
   }    
   public String getStreet() {
       return street;
   }    
   public void setStreet(String address) {
       this.street = address;
   }    public String getCity() {
       return city;
   }    public void setCity(String city) {
       this.city = city;
   }    public String getState() {
       return state;
   }    public void setState(String state) {
       this.state = state;
   }    public String getZip() {
       return zip;
   }    public void setZip(String zip) {
       this.zip = zip;
   }    public String toString() {
       return "Address id: " + getId() +
              ", street: " + getStreet() +               ", city: " + getCity() +               ", state: " + getState() +               ", zip: " + getZip();
   }

}

以下是数据库转储。

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

   Column Name: CITY,
   Column Type: VARCHAR:
   Column Value: city

   Column Name: STATE,
   Column Type: VARCHAR:
   Column Value: state

   Column Name: STREET,
   Column Type: VARCHAR:
   Column Value: street

   Column Name: ZIP,
   Column Type: VARCHAR:
   Column Value: null





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

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

   Column Name: ADDRESS_ID,
   Column Type: INTEGER:
   Column Value: 1

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