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<Employee> emps;//集合类型，因为有多个员工

public Department() {

super();

// TODO Auto-generated constructor stub

}

public Department(int id, String nameString, Set<Employee> emps) {

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<Employee> getEmps() {

return emps;

}

public void setEmps(Set<Employee> emps) {

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

<!DOCTYPE hibernate-configuration PUBLIC

"-//Hibernate/Hibernate Configuration DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

<session-factory>

<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

<property name="hibernate.connection.url">jdbc:mysql:///demo</property>

<property name="hibernate.connection.username">root</property>

<property name="hibernate.connection.password">1234</property>

<!-- 方言 针对哪个数据库Mysql -->

<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>

<!-- 在程序运动的时候，增加自动创建表的属性，在程序终止 的时候销毁，但是在表格再次使用时，会重新建 -->

<property name="hibernate.hbm2ddl.auto">update</property>

<!-- 执行的sql语句显示出来 -->

<property name="hibernate.show_sql">true</property>

<!-- 指定映射文件的位置 -->

<mapping resource="com/hbsi/domain/Department.hbm.xml" />

<mapping resource="com/hbsi/domain/Employee.hbm.xml" />

</session-factory>

</hibernate-configuration>

（4）Department的映射文件

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.hbsi.domain">

<!-- 缺省table 表明和类名是一样的 -->

<class name="Department" table="department">

<id name="id" column="id">

<generator class="native" />

</id>

<property name="name" column="name" />

<!-- 集合属性的体现 一对多 -->

<set name="emps">

<!-- 根据外键的值查询，而不是查询所有的记录-->

<key column="depart_id"/>

<!-- 告诉Hibernate emps是集合属性，是一对多的关联 -->

<one-to-many class="Employee" />

</set>

</class>

</hibernate-mapping>

（5）Employee的映射文件

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.hbsi.domain">

<class name="Employee" table="employee">

<id name="id" column="id">

<generator class="native" />

</id>

<property name="name" column="name" />

<!-- 外键的映射 (多对一) not-null="true"是使外键不为空 -->

<many-to-one name="depart" column="depart_id" not-null="true" foreign-key="指定外键的名称"/>

</class>

</hibernate-mapping>

（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<Employee> list = department.getEmps();

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

<set name="emps">

<!-- 根据外键的值查询，而不是查询所有的记录-->

<key column="depart_id"/>

<!-- 告诉Hibernate emps是集合属性，是一对多的关联 -->

<one-to-many class="Employee" />

</set>

（2）在Department中设置的是set集合类型的