JPA学习（四）

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钟渊博客 2023-01-03 10:11:28 博主文章分类：框架学习 ©著作权

文章标签 JPA Hibernate java Customer 一对多 文章分类 虚拟化云计算

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JPA一对多关联关系

/**
 * 实体类
 */
package com.jpa.helloword;


import java.util.Date;
import java.util.HashSet;
import java.util.Set;

import javax.persistence.Cacheable;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

import org.hibernate.annotations.Cache;

/**
 * @author 徐庶
 * @date 2016年12月10日
 */
@Cacheable(true)
@Table(name="JPA_CUSTOMERS")
@Entity
public class Customer {
  private  Integer id;
  private String name;
  private String email;
  private int age;
  private Date birth;
  private Date createDate;
  //一对多
  private Set<Order> orders=new HashSet<>();
  //使用@JoinColumn来映射外键列的名称
  @JoinColumn(name="CUSTOMER_ID")
  @OneToMany
  public Set<Order> getOrders() {
    return orders;
  }
  public void setOrders(Set<Order> orders) {
    this.orders = orders;
  }
  @Temporal(TemporalType.DATE)
  public Date getBirth() {
    return birth;
  }
  public void setBirth(Date birth) {
    this.birth = birth;
  }
  
  @Temporal(TemporalType.TIMESTAMP)
  public Date getCreateDate() {
    return createDate;
  }
  public void setCreateDate(Date createDate) {
    this.createDate = createDate;
  }
  @GeneratedValue(strategy=GenerationType.AUTO)
  @Id
  public Integer getId() {
    return id;
  }
  public void setId(Integer id) {
    this.id = id;
  }
  
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  }
  
  public String getEmail() {
    return email;
  }
  public void setEmail(String email) {
    this.email = email;
  }
  public int getAge() {
    return age;
  }
  public void setAge(int age) {
    this.age = age;
  }
  @Override
  public String toString() {
    return "Customer [id=" + id + ", name=" + name + ", email=" + email
        + ", age=" + age + ", birth=" + birth + ", createDate="
        + createDate + "]";
  }
  
}


/**
 * 
 */
package com.jpa.helloword;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

/**
 * @author 徐庶
 * @date 2016年12月11日
 */
@Table(name="JPA_ORDERS")
@Entity
public class Order {
  private  Integer id;
  private String OrderName;
  
 @Id
 @GeneratedValue(strategy=GenerationType.AUTO)
 public Integer getId() {
  return id;
}
public void setId(Integer id) {
  this.id = id;
}
@Column(name="ORDER_NAME")
public String getOrderName() {
  return OrderName;
}
public void setOrderName(String orderName) {
  OrderName = orderName;
}
}

测试：

//一对多测试,单向一对多执行保存时，会多出 update语句，因为多的一方插入时不会同时插入外键列。

@Test
  public void OneTomany(){
    Customer customer=new Customer();
    customer.setAge(10);
    customer.setName("tom");
    customer.setBirth(new Date());
    customer.setCreateDate(new Date());
    customer.setEmail("tom@q.com");
    Order order1=new Order();
    order1.setOrderName("TTT");
    Order order2=new Order();
    order2.setOrderName("YYY");
    customer.getOrders().add(order1);
    customer.getOrders().add(order2);
    //保存
    entityManager.persist(customer);
    entityManager.persist(order1);
    entityManager.persist(order2);
  }

//一对多查询时默认使用懒加载方式
  //可以使用(fetch=FetchType.EAGER)修改加载策略。
  @Test
  public void  oneTomanyfind(){
    Customer customer = entityManager.find(Customer.class, 6);
    System.out.println(customer.getName());
    System.err.println("------------");
    System.out.println(customer.getOrders().size());
  }

一对多的保存也可以使用@OneToMany(cascade={CascadeType.PERSIST})注解进行级联保存。

@Test
  public void OneTomany(){
    Customer customer=new Customer();
    customer.setAge(10);
    customer.setName("飞鹰");
    customer.setBirth(new Date());
    customer.setCreateDate(new Date());
    customer.setEmail("飞飞@q.com");
    Order order1=new Order();
    order1.setOrderName("飞飞1");
    Order order2=new Order();
    order2.setOrderName("飞飞2");
    customer.getOrders().add(order1);
    customer.getOrders().add(order2);
    //保存
    entityManager.persist(customer);
    //entityManager.persist(order1);
    //entityManager.persist(order2);
  }

//一对多删除时，若删除一的一端，则会把多的一端的外键置空，然后再删除。
  //可以通过@OneToMany(cascade={CascadeType.REMOVE})来修改默认的删除策略。
  @Test
  public  void oneTomanyRemove(){
    Customer customer = entityManager.find(Customer.class, 6);
    entityManager.remove(customer);
    
  }

默认情况下删除操作打印的sql语句：

Hibernate: 
    select
        customer0_.id as id1_0_0_,
        customer0_.age as age2_0_0_,
        customer0_.birth as birth3_0_0_,
        customer0_.createDate as createDa4_0_0_,
        customer0_.email as email5_0_0_,
        customer0_.name as name6_0_0_ 
    from
        JPA_CUSTOMERS customer0_ 
    where
        customer0_.id=?
Hibernate: 
    update
        JPA_ORDERS 
    set
        CUSTOMER_ID=null 
    where
        CUSTOMER_ID=?
Hibernate: 
    delete 
    from
        JPA_CUSTOMERS 
    where
        id=?