Hibernate_映射_关联关系_cascade属性、单向关联

旧城等待， 2022-06-15 21:00 241阅读 0赞

<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
       
    
    
       
    
       
    	
        
    	
        
    		
         
    			
          
    		
         
    		
         
    		
         
    		
         
        
    			
          
    			
          
    		
         
        
    	
        
    
       
    
       
    
    
       
    
       
    	
        
    	
        
    		
         
    			
          
    		
         
    		
         
    
    		
         
    		
         
    	
        
    
       
    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();
    		}
    	}