一：多对一单向关联
首先我们必须创建两个实体类
例如：Dept类
public class Dept {
private Integer deptNo;
private String dName;
private String loc;
private Set<Employee> emps=new HashSet<Employee>();
Employee类
public class Employee {
private Integer empno;
private String ename;
private Dept dept;
现在我们可以在配置文件里面配置了
Dept.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cn.entity">
<class name="Dept" table="Dept">
<id name="deptNo" column="deptNo">
<generator class="native"/>
</id>
<property name="dName" type="string" column="dName"/>
<property name="loc" type="string" column="loc"/>
<!--cascade:级联 inverse：反转 -->
<set name="emps" cascade="save-update" inverse="true" >
<key column="deptNo"></key>
<!--一对多 -->
<one-to-many class="Employee"/>
</set>
</class>
</hibernate-mapping>
Employee.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cn.entity">
<class name="Employee" table="Employee">
<id name="empno" column="empno">
<generator class="native"/>
</id>
<property name="ename" type="string" column="ename"/>
<!--多对一 -->
<many-to-one name="dept" column="deptNo" class="Dept"></many-to-one>
<set name="projects" inverse="true" table="proemp">
<key column="rempNo"></key>
<many-to-many class="Project" column="rproNo"></many-to-many>
</set>
</class>
</hibernate-mapping>
到这里，一对多 和多对一的关联 配置已经完成！！
我们一起来看看测试类
// 添加数据
private static void addDeptAndEmployee() {
Session currentSession = HibernateUtil.currentSession();
currentSession.beginTransaction();
Dept dept = new Dept();
//dept.setDeptNo(deptNo)
dept.setdName("质管部22");
dept.setLoc("北京22");
Employee emp = new Employee();
emp.setEname("龙龙");
emp.setDept(dept);//建立dept 到employee 对象的 关联
currentSession.save(emp);
currentSession.save(dept);
currentSession.getTransaction().commit();
HibernateUtil.closeSessio();
System.out.println("add ok");
}
// 级联保存 cascade:级联
private static void addDeptAndEmployeeTocascade() {
Session currentSession = HibernateUtil.currentSession();
currentSession.beginTransaction();
Dept dept = new Dept();
// dept.setDeptNo(deptNo)
dept.setdName("质管部22");
dept.setLoc("北京22");
Employee emp = new Employee();
emp.setEname("龙龙");
// 建立Dept对象 和Employee 对象的 一对多 双向关系
emp.setDept(dept);
dept.getEmps().add(emp);//
currentSession.save(dept);
currentSession.getTransaction().commit();
HibernateUtil.closeSessio();
System.out.println("add ok");
}
现在我们开始来看看多对多的关联
我们还是创建好实体类
例如：
Employee
public class Employee {
private Integer empno;
private String ename;
private Dept dept;
private Set<Project> projects=new HashSet<Project>(0);//集合 类 employee的属性
Project
public class Project {
private Integer proNo;//项目的编号
private String proName;//项目名称
private Set<Employee> employees=new HashSet<Employee>(0);//集合 类 employee的属性
注意：我还在了Oracle 工具里面创建了 另外一个表proemp ，即 连接表，你看一下外键关系就可以知道了
create table proemp( rproNo number(6), rempNo number(6) ) alter table proemp add constraints FK_rproNo FOREIGN KEY(rproNo) REFERENCES Project(prono) alter table proemp add constraints FK_rempNo FOREIGN KEY(rempNo) REFERENCES employee(empNo)
然后来配置映射文件
单向 多对多关联
Employee.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cn.entity">
<class name="Employee" table="Employee">
<id name="empno" column="empno">
<generator class="native"/>
</id>
<property name="ename" type="string" column="ename"/>
<!--多对一 -->
<many-to-one name="dept" column="deptNo" class="Dept"></many-to-one>
<set name="projects" inverse="true" table="proemp">
<key column="rempNo"></key>
<many-to-many class="Project" column="rproNo"></many-to-many>
</set>
</class>
</hibernate-mapping>
双向 多对多
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cn.entity">
<class name="Project" table="Project">
<id name="proNo" column="proNo">
<generator class="native"/>
</id>
<property name="proName" type="string" column="proName"/>
<!--配置单向多对多关联 -->
<!-- 映射project 类的employees的属性 -->
<!--cascade="save-update":表名保存或更新project对象时，会级联保存或更新与它关联的Employee对象 -->
<set name="employees" table="proemp" cascade="save-update">
<key column="rproNo"></key>
<many-to-many class="Employee" column="rempNo"></many-to-many>
</set>
</class>
</hibernate-mapping>
我们一起来看看测试类
private static void addProToEmpAndEmpToPro() {
Session session = HibernateUtil.currentSession();
session.beginTransaction();
Employee emp=new Employee();
Employee emp2=new Employee();
Project pro=new Project();
Project pro2=new Project();
emp.setEname("李四");
emp2.setEname("张三");
pro.setProName("一号项目");
pro2.setProName("二号项目");
pro.getEmployees().add(emp);
pro.getEmployees().add(emp2);
emp.getProjects().add(pro);
emp.getProjects().add(pro2);
pro2.getEmployees().add(emp);
emp.getProjects().add(pro2);
session.save(pro);
session.save(pro2);
HibernateUtil.closeSessio();
}
//保存Project 对象的同时还能保存 Employee对象
private static void addProToEmp() {
Session session = HibernateUtil.currentSession();
session.beginTransaction();
Employee emp=new Employee();
Employee emp2=new Employee();
Project pro=new Project();
Project pro2=new Project();
emp.setEname("李四");
emp2.setEname("张三");
pro.setProName("一号项目");
pro2.setProName("二号项目");
pro.getEmployees().add(emp);
pro.getEmployees().add(emp2);
pro2.getEmployees().add(emp);
session.save(pro);
session.save(pro2);
HibernateUtil.closeSessio();
}
就到这里了，有问题可以在线解答！！！！！！！！！！！！
时间： 2024-08-08 05:39:11