Hibernate One2Many映射关系

标签：hibernate

多对一映射与一对多映射：

使用部门和员工的关系来说明问题.一个部门可以有多个员工,但是一个员工只属于一个部门.

开发步骤：

(1)JavaBean的设计,Dept(部门表) Employee(员工表)

(2)映射关系

(3)测试

1.Dept和Employee Javabean

Dept

package cn.itcast.one2many;

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

public class Dept {
	private int deptId;
	private String deptName;
	private Set<Employee> emps=new HashSet<Employee>();
	public int getDeptId() {
		return deptId;
	}
	public void setDeptId(int deptId) {
		this.deptId = deptId;
	}
	public String getDeptName() {
		return deptName;
	}
	public void setDeptName(String deptName) {
		this.deptName = deptName;
	}
	public Set<Employee> getEmps() {
		return emps;
	}
	public void setEmps(Set<Employee> emps) {
		this.emps = emps;
	}
	
}

package cn.itcast.one2many;

public class Employee {
	private int empId;
	private String empName;
	private Dept dept;
	public int getEmpId() {
		return empId;
	}
	public void setEmpId(int empId) {
		this.empId = empId;
	}
	public String getEmpName() {
		return empName;
	}
	public void setEmpName(String empName) {
		this.empName = empName;
	}
	public Dept getDept() {
		return dept;
	}
	public void setDept(Dept dept) {
		this.dept = dept;
	}
}

Dept.hbm.xml

<?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="cn.itcast.one2many" auto-import="true">
	<class name="Dept" table="t_dept">
		<id name="deptId">
			<generator class="native"></generator>
		</id>
		<property name="deptName" column="deptName" length="20" type="string"></property>
		<span style="color:#ff0000;"><!-- 
			一对多的关系
			dept映射关键点
			1.指定映射的集合属性
			2.集合属性对应的集合表
			3.集合表的外键字段 "dept_id"
			4.集合元素的类型Set<>尖括号里面的
		 --></span>
		 <set name="emps" table="t_employee">
		 	<key column="dept_id"></key>
		 	<one-to-many class="Employee"/>
		 </set>
	</class>
</hibernate-mapping>

<?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="cn.itcast.one2many" auto-import="true">
	<class name="Employee" table="t_employee">
		<id name="empId">
			<generator class="native"></generator>
		</id>
		<property name="empName" column="empName" length="20" type="string"></property>
		<span style="color:#ff0000;"><!-- 
			多对一：
			1.映射的部门属性：dept
			2.映射部门的属性,对应的外键字段
			3.部门的类型
		 --></span>
		<many-to-one name="dept"  column="dep_id" class="Dept"></many-to-one>
	</class>
</hibernate-mapping>

package cn.itcast.one2many;

import org.hibernate.Transaction;
import org.hibernate.classic.Session;
import org.junit.Test;

import cn.itcast.utils.HibernateUtil;

public class App {
	@Test
	public void testOne2Many(){
		Session session = HibernateUtil.getSession();
		Transaction transaction = session.beginTransaction();
		//通过部门维护员工
		//1.部门
		Dept dept=new Dept();
		dept.setDeptName("行政部");
		//2.员工
		Employee emp_lwk=new Employee();
		emp_lwk.setEmpName("李卫康");
		Employee emp_hw=new Employee();
		emp_hw.setEmpName("韩玮");
		
		//3.关系
		dept.getEmps().add(emp_lwk);
		dept.getEmps().add(emp_hw);
		//4.保存到数据库要保存每一个对象
		session.save(emp_hw);
		session.save(emp_lwk);
		session.save(dept);
		transaction.commit();
		session.close();
		
	}
}

可以发现t_employee表中的外键约束

Hibernate One2Many映射关系

标签：hibernate

原文地址：http://blog.csdn.net/u014010769/article/details/47093873