Hibernate关联映射 映射文件的配置

时间：2021-06-17 14:39:53

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");

    }

 

我们谈到关联映射的多对多配置呢，有一种挺不好配置的，所以呢，就放到了这里给大家参考

第一种：建立多对多双向关联 拆成两个一对多

三个实体类

Employee

 private Integer empno;
     private String ename;

     private  Dept dept;
     );//集合 类 employee的属性
     );

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
private Set<ProEmp> pe=new HashSet<ProEmp>(0);

中间表

ProEmp

private Integer id;
    private Project pro;
    private Employee emp;

映射文件

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.three.entity">
    <class name="Employee" table="Employee">
        <id name="empno" column="empno">
            <generator class="native"/>
        </id>
        <property name="ename" type="string" column="ename"/>
    </class>
</hibernate-mapping>

Project.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.three.entity">
    <class name="Project" table="Project">
        <id name="proNo" column="proNo">
            <generator class="native"/>
        </id>
        <property name="proName" type="string" column="proName"/>
    </class>
</hibernate-mapping>

ProEmp.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.three.entity">
    <class name="ProEmp" table="ProEmp">
        <id name="id" column="id">
            <generator class="native"/>
        </id>
          <!-- 与员工关联 -->
        <many-to-one name="emp" column="empno" class="Employee"></many-to-one>
   <!-- -与project关联 -->
     <many-to-one name="pro" class="Project" column="proNo"></many-to-one>
    </class>
</hibernate-mapping>

大配置文件hibernate.cfg.xml

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <!-- Database connection settings -->
        <property name="connection.driver_class">
            oracle.jdbc.driver.OracleDriver
        </property>
        <property name="connection.url">
            jdbc:oracle:thin:@localhost:1521:orcl
        </property>
        <property name="connection.username">wgy</property>
        <property name="connection.password">jpp</property>

        <!-- JDBC connection pool (use the built-in) -->

        <property name="connection.pool_size">1</property>

        <!-- SQL dialect --><!-- SQL 方言 -->

        <property name="dialect">
            org.hibernate.dialect.Oracle10gDialect
        </property>

        <!-- Enable Hibernate's automatic session context management -->
        <!-- <property name="current_session_context_class">thread</property>
        -->
        <!-- Disable the second-level cache -->
        <!-- <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>
        -->
        <!-- Echo all executed SQL to stdout -->
        <property name="show_sql">true</property>

        <!-- Drop and re-create the database schema on startup -->
        <!--序列化  -->
        <property name="hbm2ddl.auto">create</property>
        <!-- <property name="hbm2ddl.auto">update</property> -->
        <!-- sql语句格式化 -->
        <property name="format_sql">true</property>
        <!-- 资源 -->

        <<mapping resource="cn/three/entity/Dept.hbm.xml" />
         <mapping resource="cn/three/entity/Employee.hbm.xml" />
         <mapping resource="cn/three/entity/Project.hbm.xml" /> 

    </session-factory>
</hibernate-configuration>

测试类看一下效果

package cn.main;

import org.hibernate.Session;

import cn.three.entity.ProEmp;
import cn.three.entity.Employee;
import cn.three.entity.Project;
import cn.util.HibernateUtil;

public class ThreeTest {
public static void main(String[] args) {
    //三表一起
        threeAddEmpAndProAndProEmp();
}
private static void threeAddEmpAndProAndProEmp() {
    Session session = HibernateUtil.currentSession();
    session.beginTransaction();
    Employee emp=new Employee();
    Project pro=new Project();
    emp.setEname("李四");
    pro.setProName("一号项目");
    ProEmp pe=new ProEmp();
    pe.setEmp(emp);
    pe.setPro(pro);
    session.save(pro);
    session.save(emp);
    session.save(pe);
    session.getTransaction().commit();
    HibernateUtil.closeSessio();
    System.out.println("add ok");

}
}

第二种：不用拆成两个一对多

只需要两个映射文件，即可

Employee.hbm.xml

复制代码
<?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>
        <!--多对多双向关联  -->
        <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>
Project.hbm.xml


复制代码
<?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>
测试类


复制代码
private static void addProToEmpAndEmpToPro() {
    Session session = HibernateUtil.currentSession();
    session.beginTransaction();
    Employee emp=new Employee();

    Project pro=new Project();

    emp.setEname("李四");

    pro.setProName("一号项目");

    pro.getEmployees().add(emp);
    session.save(pro);
    session.getTransaction().commit();
    HibernateUtil.closeSessio();
    System.out.println("add ok");

这样就可以了，有问题在线解答！！！！！

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