Hibernate关联映射 --- 一对多实例分析（双向关联）
Hibernate关联映射 --- 一对多实例分析（双向关联）
一 概念
最典型的例子是Department和Employee的关系，双向的关联
二 代码分析
（1）Department表
package com.hbsi.domain;
import java.util.Set;
//部门类
public class Department {
//实现一对多
private int id;
private String nameString;
private Set
public Department() {
super();
// TODO Auto-generated constructor stub
}
public Department(int id, String nameString, Set
super();
this.id = id;
this.nameString = nameString;
this.emps = emps;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getNameString() {
return nameString;
}
public void setNameString(String nameString) {
this.nameString = nameString;
}
public Set
return emps;
}
public void setEmps(Set
this.emps = emps;
}
@Override
public String toString() {
return "Department [id=" + id + ", nameString=" + nameString
+ ", emps=" + emps + "]";
}
}
（2）Employee类
package com.hbsi.domain;
//员工类 一般主鍵是建在多的一方
public class Employee {
private int id;
private String name;
//通过id查询员工，通过员工 查找部门的话，只能找到部门的id,得不到部门的其他信息
// 得到的是一个 对象，可以得到员工对应的部门的详细信息
private Department depart;
public Employee() {
super();
// TODO Auto-generated constructor stub
}
public Employee(int id, String name, Department depart) {
super();
this.id = id;
this.name = name;
this.depart = depart;
}
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 Department getDepart() {
return depart;
}
public void setDepart(Department depart) {
this.depart = depart;
}
public String toString() {
return "Employee [id=" + id + ", name=" + name + ", depart=" + depart
+ "]";
}
}
（3）配置文件
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
（4）Department的映射文件
"1.0"?>
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
（5）Employee的映射文件
"1.0"?>
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
（6）测试插入和查询
package com.hbsi.test;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.hbsi.domain.Department;
import com.hbsi.domain.Employee;
import com.hbsi.hibernate.utils.HibernateUtil;
public class One2Many {
public static void main(String[] args) {
//add();
queryDepartment(5);
}
static Department add() {
Session session = null;
Transaction transaction = null;
try {
session = HibernateUtil.getSession();
transaction = session.beginTransaction();
// 添加部门
Department department = new Department();
department.setName("老王公司 one");
Employee employee1 = new Employee();
employee1.setName("老王");
employee1.setDepart(department);// 员工对象和部门对象建立关联
Employee employee2 = new Employee();
employee2.setName("老王王");
employee2.setDepart(department);
session.save(department);
session.save(employee1);
session.save(employee2);
transaction.commit();
return department;
} finally {
if (session != null) {
session.close();
}
}
}
// 查询部门的所有员工
static Department queryDepartment(int depId) {
Session session = null;
try {
session = HibernateUtil.getSession();
Department department = (Department) session.get(Department.class,depId);
System.out.println("部门名字为："+department.getName()+"--"+department.getEmps().size()+"个员工");
return department;
查询姓名并遍历输出
Set
for(Employee entities:list){
System.out.println(entities.getName());
}
} finally {
if (session != null) {
session.close();
}
}
}
}
注：
（1）在一的一方映射文件中的最重要的是
（2）在Department中设置的是set集合类型的