Hibernate关联关系映射之一对多关联关系

package entity;

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

public class Department {
	private Integer id;
	private String name;
	private Set employees = new HashSet();
	public Integer getId() {
	return id;
	}
	public void setId(Integer id) {
	this.id = id;
	}
	public String getName() {
	return name;
	}
	public void setName(String name) {
	this.name = name;
	}
	public Set getEmployees() {
	return employees;
	}
	public void setEmployees(Set employees) {
	this.employees = employees;
	}
	
	
}

package entity;

public class Employee {
	private Integer id;
	private String name;
	private Department department;
	public Integer getId() {
	return id;
	}
	public void setId(Integer id) {
	this.id = id;
	}
	public String getName() {
	return name;
	}
	public void setName(String name) {
	this.name = name;
	}
	public Department getDepartment() {
	return department;
	}
	public void setDepartment(Department department) {
	this.department = department;
	}
	
	
}

package test;

import static org.junit.Assert.*;

import java.util.Iterator;
import java.util.Set;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.Transaction;

import entity.Department;
import entity.Employee;
import factory.HibernateSessionFactory;

public class Test {

	private Session session = null;
	private Transaction tran = null;

	//保存对象
	@org.junit.Test
	public void test() {
	session = HibernateSessionFactory.getSession();
	tran = session.beginTransaction();
	try {
	//新建对象
	Department de = new Department();
	de.setId(3);
	de.setName("研发部");

	Employee e1 = new Employee();
	e1.setId(1);
	e1.setName("张三");

	Employee e2 = new Employee();
	e2.setId(2);
	e2.setName("李四");

	//建立关系映射
	de.getEmployees().add(e1);
	de.getEmployees().add(e2);
	e1.setDepartment(de);
	e2.setDepartment(de);

	//保存数据
	session.save(de);
	session.save(e1);
	session.save(e2);
	tran.commit();
	} catch (Exception e) {
	tran.rollback();
	}
	}

	//根据部门查询员工
	@org.junit.Test
	public void getDepartment() {
	session = HibernateSessionFactory.getSession();
	String hql = "FROM Department d where d.id = 2";
	Query query = session.createQuery(hql);
	Department de = (Department) query.uniqueResult();
	Set set = de.getEmployees();
	Iterator it = set.iterator();
	while (it.hasNext()) {
	Employee e = (Employee) it.next();
	System.out.println(e.getName());
	}
	}

	//根据员工查询部门
	@org.junit.Test
	public void getEmployee() {
	session = HibernateSessionFactory.getSession();
	String hql = "FROM Employee e where e.id=1";
	Query query = session.createQuery(hql);
	Employee e = (Employee) query.uniqueResult();
	System.out.println(e.getName() + "属于" + e.getDepartment().getName());

	}

	// 解除关联关系，相当于某一个员工离开原来部门，并不删除两个表中数据
	// 从员工方删除
	@org.junit.Test
	public void removeRelation() {
	session = HibernateSessionFactory.getSession();
	tran = session.beginTransaction();
	try {
	Department de = new Department();
	de.setId(1);
	de.setName("宣传部");
	session.save(de);
	Employee e = (Employee) session.get(Employee.class, 3);
	e.setDepartment(de);
	session.save(e);
	tran.commit();
	} catch (Exception e) {
	tran.rollback();
	}
	}

	// 删除员工方
	@org.junit.Test
	public void deleteEmployee() {
	session = HibernateSessionFactory.getSession();
	tran = session.beginTransaction();
	try {
	Employee e = (Employee) session.get(Employee.class, 4);
	session.delete(e);
	tran.commit();
	} catch (Exception e) {
	tran.rollback();
	}
	}

	// 删除部门
	@org.junit.Test
	public void deleteDepartment() {
	session = HibernateSessionFactory.getSession();
	tran = session.beginTransaction();
	try {
	Department de = (Department) session.get(Department.class, 1);
	/*
	 * 如果没有关联的员工，能删除
	 * 如果有关联的员工，且inverse属性为true,由于由不能维护关联，所以会直接执行删除，就会有异常
	 * 如果有关联的与昂，且inverse属性为false，由于可以维护关联关系，他就会先把关联的员工的外键设为null。在删除
	 */
	session.delete(de);
	tran.commit();
	} catch (Exception e) {
	tran.rollback();
	}
	}
}