JPA双向关联多对一映射

JPA双向关联多对一映射

SQL

create   table  Department
(
   id                    int   not   null  auto_increment,
   name                  varchar ( 20 ),
    primary   key  (id)
);

create   table  Employee
(
   id                    int   not   null  auto_increment,
   name                  varchar ( 20 ),
   deptid                int ,
    primary   key  (id)
);

alter   table  Employee  add   constraint  FK_Reference_1  foreign   key  (deptid)
       references  Department (id)  on   delete   restrict   on   update   restrict ;

Department.java

package  com.many2one.bean;

import  java.io.Serializable;
import  java.util.Set;

import  javax.persistence.Column;
import  javax.persistence.Entity;
import  javax.persistence.GeneratedValue;
import  javax.persistence.GenerationType;
import  javax.persistence.Id;
import  javax.persistence.OneToMany;
import  javax.persistence.Table;

@SuppressWarnings( " serial " )
@Entity
@Table(name = " department " ,catalog = " jpa_many2one " )
public   class  Department   implements  Serializable{
    
     private   int  id;
     private  String name;
     private  Set < Employee >  sets;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = " id " )
     public   int  getId() {
         return  id;
    }
     public   void  setId( int  id) {
         this .id  =  id;
    }
    @Column(name = " name " )
     public  String getName() {
         return  name;
    }
     public   void  setName(String name) {
         this .name  =  name;
    }
    @OneToMany(mappedBy = " department " )
     public  Set < Employee >  getSets() {
         return  sets;
    }
     public   void  setSets(Set < Employee >  sets) {
         this .sets  =  sets;
    }
    
    
}

Employee.java

package  com.many2one.bean;

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

@Entity
@Table(name = " employee " ,catalog = " jpa_many2one " )
public   class  Employee {
    
     private   int  id;
     private  String name;
     private  Department department;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = " id " )
     public   int  getId() {
         return  id;
    }
     public   void  setId( int  id) {
         this .id  =  id;
    }
    @Column(name = " name " )
     public  String getName() {
         return  name;
    }
     public   void  setName(String name) {
         this .name  =  name;
    }
    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = " deptid " )
     public  Department getDepartment() {
         return  department;
    }
     public   void  setDepartment(Department department) {
         this .department  =  department;
    }
    
    
}

persistence.xml

<? xml version="1.0" encoding="UTF-8" ?>
< persistence  xmlns ="http://java.sun.com/xml/ns/persistence"
    xmlns:xsi ="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation ="http://java.sun.com/xml/ns/persistence
    http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"  version ="1.0" >
    
     < persistence-unit  name ="JPA_Many2OnePU"  transaction-type ="RESOURCE_LOCAL" >
         < provider > org.hibernate.ejb.HibernatePersistence </ provider >
         < class > com.many2one.bean.Department </ class >
         < class > com.many2one.bean.Employee </ class >
           < properties >
             < property  name  = "hibernate.connection.driver_class"  value  = "com.mysql.jdbc.Driver" />
             < property  name  = "hibernate.connection.url"  value  = "jdbc:mysql://localhost:3306/jpa_many2one" />
             < property  name  = "hibernate.connection.username"  value  = "root" />
             < property  name  = "hibernate.connection.password"  value  = "root" />
             < property  name  = "hibernate.show_sql"  value  = "true" />
             < property  name  = "hibernate.format_sql"  value  = "true" />
           </ properties >
     </ persistence-unit >
  
</ persistence >

JPAUtil.java

package  com.many2one.util;

import  javax.persistence.EntityManager;
import  javax.persistence.EntityManagerFactory;
import  javax.persistence.Persistence;

public   class  JPAUtil {
    
     private   static  EntityManager entityManager;
     public   static  EntityManager getInstance(){
         if (entityManager != null ){
             return  entityManager;
        } else {
             return  makeInstance();
        }
    }
     private   static   synchronized  EntityManager makeInstance() {
         if (entityManager == null ){
            EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory( " JPA_Many2OnePU " );
             return  entityManagerFactory.createEntityManager();
        }
         return   null ;
    }
}

@Test
     public   void  select(){
        EntityManager entityManager = JPAUtil.getInstance();
        Employee employee = entityManager.find(Employee. class ,  1 );
        System.out.println( " 雇员是: " + employee.getName());
        System.out.println( " 部门是: " + employee.getDepartment().getName());
    }
    
    @Test
     public   void  insert(){
        EntityManager entityManager = JPAUtil.getInstance();
        EntityTransaction entityTransaction = entityManager.getTransaction();
         try  {
            entityTransaction.begin();
            Department department = new  Department();
            department.setName( " 软件研发部 " );
            Employee employee = new  Employee();
            employee.setName( " 张三 " );
            employee.setDepartment(department);
            entityManager.persist(employee);
            entityTransaction.commit();
        }  catch  (Exception e) {
            e.printStackTrace();
            entityTransaction.rollback();
        }
    }