Hibernate_映射_关联关系_一对多多对一映射2、inverse属性
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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();
}
}
}
<!-- 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
-->
<set name="employee" inverse="false">
<key column="departmentId" />
<one-to-many class="Employee" />
</set>
// 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();
}
}
