Hibernate_映射_关联关系_cascade属性、单向关联

		<!-- employee属性,Set集合,表达的是本类与Employee的一对多关系 
			class属性：关联的实体类型
			key子元素：对方表中的外键列(多方的那个表)
			
			inverse属性：
				默认为false,表示本方维护关联关系。
				如果为true,表示本方不维护关联关系。
				只是影响是否能设置外键的值(设成有效值或者是null值),对获取信息没有影响
			
			cascade属性：
				默认为none,代表不级联。
				级联是指操作主对象时,对关联的对象也做相同的操作
				可设为：delete,save-update,all,none ...
		-->
		<set name="employee" cascade="all">
			<key column="departmentId" />
			<one-to-many class="Employee" />
		</set>

一对一,一对多,使用级联
	cascade属性：
		默认为none,代表不级联。
		级联是指操作主对象时,对关联的对象也做相同的操作
		可设为：delete,save-update,all,none ...
		
		<set name="employee" cascade="all">
			<key column="departmentId" />
			<one-to-many class="Employee" />
		</set>
双向关联
单向关联：
	单向多对一
	单向一对多
	单向多对多

值类型的集合
	集合元素是普通类型
实体类型的集合
	集合元素是另外一个实体

	一对多								     多对一
Department.hbm.xml							Employee.hbm.xml
	要说明的信息有：						要说明的信息有：
	1,集合表(员工表)							1,关联的是什么类型
	2,集合外键								2,外键列
	3,集合元素 									
		关联的实例类型<?xml version="1.0"?>



<?xml version="1.0"?>



package cn.itcast.f_hbm_oneToMany;

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

/**
 * 部门
 * 
 * @author 风清杨
 * @version V3.0
 * 
 */
public class Department {
	/** 部门id */
	private Integer id;
	/** 部门名称 */
	private String name;
	/** 员工信息 */
	private Set employee = new HashSet();// 关联的很多员工

	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 getEmployee() {
		return employee;
	}

	public void setEmployee(Set employee) {
		this.employee = employee;
	}

	@Override
	public String toString() {
		return "Department [id=" + id + ", name=" + name + "]";
	}

}
package cn.itcast.f_hbm_oneToMany;

/**
 * 员工部门
 * 
 * @author 风清杨
 * @version V3.0
 * 
 */
public class Employee {
	/** 员工编号 */
	private Integer id;
	/** 员工姓名 */
	private String name;

	/** 员工部门 */
	private Department department;// 关联的部门对象

	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;
	}

	@Override
	public String toString() {
		return "Employee [id=" + id + ", name=" + name + "]";
	}

}
package cn.itcast.f_hbm_oneToMany;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.Test;

/**
 * 应用程序操作类
 * 
 * @author 风清杨
 * @version V3.0
 * 
 */
public class App {
	private static SessionFactory sessionFactory = new Configuration()//
			.configure()//
			.addClass(Department.class)//
			.addClass(Employee.class)//
			.buildSessionFactory();

	// 保存,有关联关系
	@Test
	public void testSave() throws Exception {
		Session session = sessionFactory.openSession();
		Transaction tx = null;
		try {
			tx = session.beginTransaction();
			// ------------------------------------

			// 新建对象
			Department department = new Department();
			department.setName("开发部");

			Employee employee1 = new Employee();
			employee1.setName("张三");

			Employee employee2 = new Employee();
			employee2.setName("李四");

			// 关联起来
			employee1.setDepartment(department);
			employee2.setDepartment(department);
			department.getEmployee().add(employee1);
			department.getEmployee().add(employee2);

			// 保存
			session.save(department);
			session.save(employee1);
			session.save(employee2);
			// ------------------------------------
			tx.commit();
		} catch (RuntimeException e) {
			tx.rollback();
			throw e;
		} finally {
			session.close();
		}
	}

	// 获取,可以获取到关联的对方
	@Test
	public void testGet() throws Exception {
		Session session = sessionFactory.openSession();
		Transaction tx = null;
		try {
			tx = session.beginTransaction();
			// ------------------------------------

			// 获取一方数据,并显示另一方信息
			//Department department = (Department) session.get(Department.class,
			// 1);
			// System.out.println(department);
			// System.out.println(department.getEmployee());
			Employee employee = (Employee) session.get(Employee.class, 1);
			System.out.println(employee);
			System.out.println(employee.getDepartment());

			// ------------------------------------
			tx.commit();
		} catch (RuntimeException e) {
			tx.rollback();
			throw e;
		} finally {
			session.close();
		}
	}
}

维护关联关系：
	就是设置外键列的值。		
			// 解除关联关系
	@Test
	public void testRemoveRelation() throws Exception {
		Session session = sessionFactory.openSession();
		Transaction tx = null;
		try {
			tx = session.beginTransaction();
			// ------------------------------------

			// 从员工解除
			// Employee employee = (Employee) session.get(Employee.class, 1);
			// employee.setDepartment(null);

			// 从部门解除(与inverse有关系,为false时可以解除)
			Department department = (Department) session.get(Department.class,
					1);
			department.getEmployee().clear();

			session.update(department);
			// ------------------------------------
			tx.commit();
		} catch (RuntimeException e) {
			tx.rollback();
			throw e;
		} finally {
			session.close();
		}
	}

	// 删除对象,对关联对象的影响
	@Test
	public void testDelete() throws Exception {
		Session session = sessionFactory.openSession();
		Transaction tx = null;
		try {
			tx = session.beginTransaction();
			// ------------------------------------

			// 删除员工方(多方)对对方没有影响
			// Employee employee = (Employee) session.get(Employee.class, 2);
			// session.delete(employee);

			// 删除部门方(一方)
			// a,如果没有关联的员工：
			// b,如果有关联的员工且inverse=true,由于不能维护关联关系,所以会直接执行删除,就会有异常。
			// c,如果有关联的员工且inverse=false,由于可以维护关联关系,它就会先把关联的员工的外键列设为null值,再删除自已。
			Department department = (Department) session.get(Department.class,
					1);
			// department.getEmployee().clear();
			session.delete(department);

			// ------------------------------------
			tx.commit();
		} catch (RuntimeException e) {
			tx.rollback();
			throw e;
		} finally {
			session.close();
		}
	}