惠州​分享Java中的JPA一对多映射键实例_北大青鸟IT学校

Java是现在非常主流的编程语言之一，很多人想转行学习Java。那么下面惠州北大青鸟老师给大家分享Java中的JPA一对多映射键实例，希望对大家的学习有帮助。

实例

下面的代码来自Person.java。

package cn.w3cschool.common;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToOne;

@Entitypublic class Person {
 @Id
 @GeneratedValue(strategy=GenerationType.IDENTITY)  private long id;  
 private String name;
 
 @ManyToOne  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 + "]";
 }

}

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(){
   Department d = new Department();
   d.setName("Design");

   Person p1 = new Person("Tom");
   p1.setDepartment(d);

   Person p2 = new Person("Jack");
   p2.setDepartment(d);
   
   d.getPersons().add(p1);
   d.getPersons().add(p2);
   
   em.persist(p1);
   em.persist(p2);
   em.persist(d);

 }
 @PersistenceContext  private EntityManager em;
}

下面的代码来自Department.java。

package cn.w3cschool.common;

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

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

@Entitypublic class Department implements java.io.Serializable{
 @Id
 @GeneratedValue(strategy=GenerationType.IDENTITY)  private long id;  
 private String name;
 
 @OneToMany(targetEntity=Person.class, mappedBy="department")
 @MapKey(name="id")  private Set<Person> persons = new HashSet<Person>();  
 public Set<Person> getPersons() {
   return persons;
 }  public void setPersons(Set<Person> persons) {
   this.persons = persons;
 }  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 + ", persons=" + persons
       + "]";
 }

}

以下是数据库转储。

Table Name: DEPARTMENT
Row:
   Column Name: ID,
   Column Type: BIGINT:
   Column Value: 1

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





Table Name: PERSON
Row:
   Column Name: ID,
   Column Type: BIGINT:
   Column Value: 1

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

   Column Name: DEPARTMENT_ID,
   Column Type: BIGINT:
   Column Value: 1

Row:
   Column Name: ID,
   Column Type: BIGINT:
   Column Value: 2

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

   Column Name: DEPARTMENT_ID,
   Column Type: BIGINT:
   Column Value: 1

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Java

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