Hibernate_映射_关联关系_cascade属性、单向关联-蒲公英云

<!-- 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
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();
        }
    }