详解hibernate双向多对多关联映射XML与注解版

双向多对多关联映射原理:

假设，一个员工可能有多个角色，一个角色可能有多个员工，从员工或角色的角度看，这就是多对多的关系，不管从哪一个角度看，都是多对多的联系。多对多关联映射关系一般采用中间表的形式来实现，即新增一种包含关联双方主键的表。实现多对多关联关系，在数据库底层通过添加中间表指定关联关系，而在hibernate框架在双方的实体中添加一个保存对方的集合，在双方的映射文件中使用<set>元素和<many-to-many>元素进行关联关系的配置。

如下图所示：

(1)XML版

Role类:

package Hibernate_demo1.Demo15.Entity;

import java.util.Set;

public class Role {

  private String id;
  private String rame;
  private Set<User> users;


  public String getId() {
    return id;
  }
  public void setId(String id) {
    this.id = id;
  }
  public String getRame() {
    return rame;
  }
  public void setRame(String rame) {
    this.rame = rame;
  }
  public Set<User> getUsers() {
    return users;
  }
  public void setUsers(Set<User> users) {
    this.users = users;
  }
}

User类:

package Hibernate_demo1.Demo15.Entity;

import java.util.Set;

public class User {

  private String id;
  private String uname;
  private Set<Role> roles;



  public String getId() {
    return id;
  }
  public void setId(String id) {
    this.id = id;
  }
  public String getUname() {
    return uname;
  }
  public void setUname(String uname) {
    this.uname = uname;
  }
  public Set<Role> getRoles() {
    return roles;
  }
  public void setRoles(Set<Role> roles) {
    this.roles = roles;
  }


}

Role.hbm.xml映射类:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
  "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
  "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
  <class name="Hibernate_demo1.Demo15.Entity.Role" table="role">
    <id name="id" type="java.lang.String">
      <column name="id"/>
      <generator class="uuid">
      </generator>
    </id>
    <property name="rame" column="rname"/>

    <set name="users" table="user_role">
      <key column="roleid"></key>
      <many-to-many class="Hibernate_demo1.Demo15.Entity.User" column="userid"></many-to-many>
    </set>
  </class>
</hibernate-mapping>

User.hbm.xml映射类:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
  "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
  "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
  <class name="Hibernate_demo1.Demo15.Entity.User" table="user">
    <id name="id">
      <generator class="uuid">
      </generator>
    </id>

    <property name="uname" column="uname"/>

     <set name="roles" table="user_role">
      <key column="userid"/>
      <many-to-many class="Hibernate_demo1.Demo15.Entity.Role" column="roleid" />
    </set>
  </class>
</hibernate-mapping>

测试类:

package Hibernate_demo1.Demo15;

import java.util.HashSet;
import java.util.Set;

import org.hibernate.Session;

import Hibernate_demo1.Demo15.Entity.Role;
import Hibernate_demo1.Demo15.Entity.User;
import Hibernate_demo1.Demo15.Util.HibernateUtils;



public class App
{
  public static void main( String[] args )
  {

    Session session = null;
    try{

      session = HibernateUtils.getSession();
      session.beginTransaction();


      Role r1 = new Role();
      r1.setRame("数据录入人员");
      session.save(r1);

      Role r2 = new Role();
      r2.setRame("商务主管");
      session.save(r2);

      Role r3 = new Role();
      r3.setRame("商务经理");
      session.save(r3);

      Role r4 = new Role();
      r4.setRame("项目会计");
      session.save(r4);

      User u1 = new User();
      u1.setUname("张三");
      Set<Role> u1Roles = new HashSet<Role>();
      u1Roles.add(r1);
      u1Roles.add(r2);
      u1.setRoles(u1Roles);
      session.save(u1);

      User u2 = new User();
      u2.setUname("李四");
      Set<Role> u2Roles = new HashSet<Role>();
      u2Roles.add(r1);
      u2Roles.add(r2);
      u2Roles.add(r3);
      u2.setRoles(u2Roles);
      session.save(u2);

      User u3 = new User();
      u3.setUname("王五");
      Set<Role> u3Roles = new HashSet<Role>();
      u3Roles.add(r3);
      u3Roles.add(r4);
      u3.setRoles(u3Roles);
      session.save(u3);


      session.getTransaction().commit();
    }catch(Exception e){
      e.printStackTrace();
      session.getTransaction().rollback();
    }finally{
      HibernateUtils.closeSession(session);
    }
  }
}

执行结果:

Hibernate:
  insert
  into
    role
    (rname, id)
  values
    (?, ?)
Hibernate:
  insert
  into
    role
    (rname, id)
  values
    (?, ?)
Hibernate:
  insert
  into
    role
    (rname, id)
  values
    (?, ?)
Hibernate:
  insert
  into
    role
    (rname, id)
  values
    (?, ?)
Hibernate:
  insert
  into
    user
    (uname, id)
  values
    (?, ?)
Hibernate:
  insert
  into
    user
    (uname, id)
  values
    (?, ?)
Hibernate:
  insert
  into
    user
    (uname, id)
  values
    (?, ?)
Hibernate:
  insert
  into
    user_role
    (userid, roleid)
  values
    (?, ?)
Hibernate:
  insert
  into
    user_role
    (userid, roleid)
  values
    (?, ?)
Hibernate:
  insert
  into
    user_role
    (userid, roleid)
  values
    (?, ?)
Hibernate:
  insert
  into
    user_role
    (userid, roleid)
  values
    (?, ?)
Hibernate:
  insert
  into
    user_role
    (userid, roleid)
  values
    (?, ?)
Hibernate:
  insert
  into
    user_role
    (userid, roleid)
  values
    (?, ?)
Hibernate:
  insert
  into
    user_role
    (userid, roleid)
  values
    (?, ?)

数据库内容为:

user表:

role表:

user_role表:

(2)注解版

Role类:

package Hibernate_demo1.Demo16.Entity;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

import org.hibernate.annotations.GenericGenerator;

@Entity
@Table(name="role")
public class Role {

  @Id
    @GenericGenerator(name="uuidGenerator", strategy="uuid")
    @GeneratedValue(generator="uuidGenerator")
  private String id;

  @Column(name="rname")
  private String rame;

  @ManyToMany(cascade=CascadeType.REFRESH,mappedBy="roles")
  private Set<User> users=new HashSet<User>();




  public String getId() {
    return id;
  }
  public void setId(String id) {
    this.id = id;
  }
  public String getRame() {
    return rame;
  }
  public void setRame(String rame) {
    this.rame = rame;
  }
  public Set<User> getUsers() {
    return users;
  }
  public void setUsers(Set<User> users) {
    this.users = users;
  }
}

User类:

package Hibernate_demo1.Demo16.Entity;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
import javax.persistence.JoinColumn;

import org.hibernate.annotations.GenericGenerator;

@Entity
@Table(name="user")
public class User {

  @Id
    @GenericGenerator(name="uuidGenerator", strategy="uuid")
    @GeneratedValue(generator="uuidGenerator")
  private String id;

  @Column(name="uname")
  private String uname;

  /*
   * @ManyToMany表示多对多关联，对于这种关联极少数情况会使用级联删除，我这里设置的是级联刷新；
   * 因为有中间表的存在这里使用@JoinTable来设置关联表后面的name配置的是关联表的名称
   * inverseJoinColumn配置的是关系被维护一方主键对应的中间表字段
   * joinColumn配置的是关系维护方主键对应的中间表字段。
   */
  @ManyToMany(cascade=CascadeType.REFRESH)
  @JoinTable(name="user_role",inverseJoinColumns=@JoinColumn(name="roleid"),joinColumns=@JoinColumn(name="userid"))
  private Set<Role> roles=new HashSet<Role>();



  public String getId() {
    return id;
  }
  public void setId(String id) {
    this.id = id;
  }
  public String getUname() {
    return uname;
  }
  public void setUname(String uname) {
    this.uname = uname;
  }
  public Set<Role> getRoles() {
    return roles;
  }
  public void setRoles(Set<Role> roles) {
    this.roles = roles;
  }


}

测试类:

package Hibernate_demo1.Demo16;

import java.util.HashSet;
import java.util.Set;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import Hibernate_demo1.Demo16.Entity.Role;
import Hibernate_demo1.Demo16.Entity.User;


public class Test {

  public static void main(String[] args) {


    SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
    Session session = sessionFactory.getCurrentSession();
    Transaction tx = session.beginTransaction();


    //创建两个用户
    User us1=new User();
    us1.setUname("小明");

    User us2=new User();
    us2.setUname("小黑");

    //创建用户集合
    Set<User> su=new HashSet<User>();
    su.add(us1);
    su.add(us2);


    //创建两个角色
    Role ro1=new Role();
    ro1.setRame("程序员");
    ro1.setUsers(su);

    Role ro2=new Role();
    ro2.setRame("技术经理");
    ro2.setUsers(su);


    //创建角色集合
    Set<Role> sr=new HashSet<Role>();
    sr.add(ro1);
    sr.add(ro2);

    //往用户添加角色集合
    us1.setRoles(sr);
    us2.setRoles(sr);

    //保存用户和角色
    session.save(us1);
    session.save(us2);
    session.save(ro1);
    session.save(ro2);


    tx.commit();
    session.close();
  }

}

执行结果如下:

Hibernate:
  insert
  into
    user
    (uname, id)
  values
    (?, ?)
Hibernate:
  insert
  into
    user
    (uname, id)
  values
    (?, ?)
Hibernate:
  insert
  into
    role
    (rname, id)
  values
    (?, ?)
Hibernate:
  insert
  into
    role
    (rname, id)
  values
    (?, ?)
Hibernate:
  insert
  into
    user_role
    (userid, roleid)
  values
    (?, ?)
Hibernate:
  insert
  into
    user_role
    (userid, roleid)
  values
    (?, ?)
Hibernate:
  insert
  into
    user_role
    (userid, roleid)
  values
    (?, ?)
Hibernate:
  insert
  into
    user_role
    (userid, roleid)
  values
    (?, ?)

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持脚本之家。