详解hibernate双向多对多关联映射XML与注解版
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2024-02-22 16:46:16
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...
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。