MyBatis08_多表查询二
本教程源码请访问:tutorial_demo
本案例分析“多对多”关系时,使用用户表(user)、用户角色表(user_role)和角色表(role)来分析。通过前面的学习,我们使用MyBatis实现一对多关系的维护。多对多关系其实我们可以看成是双向的一对多关系。
一、实现Role到User的多对多
1.1、编写用户User实体类
package org.codeaction.domain;
import java.io.Serializable;
import java.util.Date;
import java.util.List;
public class User implements Serializable {
private Integer id;
private String username;
private Date birthday;
private String sex;
private String address;
//多对多的关系映射:一个用户可以拥有多个角色
private List<Role> roles;
public List<Role> getRoles() {
return roles;
}
public void setRoles(List<Role> roles) {
this.roles = roles;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + '\'' +
", birthday=" + birthday +
", sex='" + sex + '\'' +
", address='" + address + '\'' +
'}';
}
}
1.2、编写角色Role实体类
package org.codeaction.domain;
import java.io.Serializable;
import java.util.List;
public class Role implements Serializable {
private Integer roleId;
private String roleName;
private String roleDesc;
//多对多的关系映射:一个角色可以赋予多个用户
private List<User> users;
public List<User> getUsers() {
return users;
}
public void setUsers(List<User> users) {
this.users = users;
}
public Integer getRoleId() {
return roleId;
}
public void setRoleId(Integer roleId) {
this.roleId = roleId;
}
public String getRoleName() {
return roleName;
}
public void setRoleName(String roleName) {
this.roleName = roleName;
}
public String getRoleDesc() {
return roleDesc;
}
public void setRoleDesc(String roleDesc) {
this.roleDesc = roleDesc;
}
@Override
public String toString() {
return "Role{" +
"roleId=" + roleId +
", roleName='" + roleName + '\'' +
", roleDesc='" + roleDesc + '\'' +
'}';
}
}
1.3、编写Role持久层接口
package org.codeaction.dao;
import org.codeaction.domain.Role;
import java.util.List;
public interface IRoleDao {
List<Role> findAll();
}
1.4、编写持久层接口映射配置文件IRoleDao.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.codeaction.dao.IRoleDao">
<resultMap id="RoleMap" type="org.codeaction.domain.Role">
<id property="roleId" column="rid"></id>
<result property="roleName" column="role_name"></result>
<result property="roleDesc" column="role_desc"></result>
<collection property="users" ofType="org.codeaction.domain.User">
<id property="id" column="id"></id>
<result property="username" column="username"></result>
<result property="birthday" column="birthday"></result>
<result property="sex" column="sex"></result>
<result property="address" column="address"></result>
</collection>
</resultMap>
<!-- 配置查询所有 -->
<select id="findAll" resultMap="RoleMap">
select
r.id rid, r.ROLE_NAME, r.ROLE_DESC, u.*
from
role r
left join user_role ur on r.id = ur.rid
left join user u on ur.uid = u.id;
</select>
</mapper>
1.5、编写测试类
package org.codeaction.test;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.codeaction.dao.IRoleDao;
import org.codeaction.dao.IUserDao;
import org.codeaction.domain.Role;
import org.codeaction.domain.User;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
public class MyBatisTest {
private InputStream in;
private SqlSession session;
@Before
public void init() throws IOException {
//读取配置文件
in = Resources.getResourceAsStream("SqlMapConfig.xml");
//创建SqlSessionFactory工厂
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(in);
//使用工厂生产SqlSession对象
session = factory.openSession();
}
@After
public void destroy() throws IOException {
//提交事务
session.commit();
//释放资源
session.close();
in.close();
}
@Test
public void testFindAllRole() throws IOException {
//使用SqlSession创建Dao接口的代理对象
IRoleDao roleDao = session.getMapper(IRoleDao.class);
//使用代理对象执行方法
List<Role> roles = roleDao.findAll();
roles.forEach(role -> {
System.out.println(role);
role.getUsers().forEach(System.out::println);
});
}
}
运行测试方法,控制台输出如下:
Role{roleId=1, roleName='院长', roleDesc='管理整个学院'}
User{id=41, username='王一', birthday=Tue Dec 27 17:47:08 CST 2011, sex='男', address='北京'}
User{id=45, username='Max', birthday=Tue May 04 12:04:06 CST 2010, sex='男', address='西宁'}
Role{roleId=2, roleName='总裁', roleDesc='管理整个公司'}
User{id=41, username='王一', birthday=Tue Dec 27 17:47:08 CST 2011, sex='男', address='北京'}
Role{roleId=3, roleName='校长', roleDesc='管理整个学校'}
二、实现User到Role的多对多
2.1、编写User持久层接口
package org.codeaction.dao;
import org.codeaction.domain.User;
import java.util.List;
public interface IUserDao {
List<User> findAll();
User findById(Integer id);
}
2.2、编写持久层接口映射配置文件IUserDao.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.codeaction.dao.IUserDao">
<resultMap id="UserMap" type="org.codeaction.domain.User">
<id property="id" column="id"></id>
<result property="username" column="username"></result>
<result property="birthday" column="birthday"></result>
<result property="sex" column="sex"></result>
<result property="address" column="address"></result>
<collection property="roles" ofType="org.codeaction.domain.Role">
<id property="roleId" column="rid"></id>
<result property="roleName" column="role_name"></result>
<result property="roleDesc" column="role_desc"></result>
</collection>
</resultMap>
<!-- 配置查询所有 -->
<select id="findAll" resultMap="UserMap">
select
u.*, r.id rid, r.ROLE_NAME, r.ROLE_DESC
from
user u
left join user_role ur on u.id = ur.uid
left join role r on ur.rid = r.id;
</select>
</mapper>
2.3、添加测试方法
@Test
public void testFindAllUser() throws Exception {
IUserDao userDao = session.getMapper(IUserDao.class);
List<User> users = userDao.findAll();
users.forEach(user -> {
System.out.println(user);
user.getRoles().forEach(System.out::println);
});
}
运行测试方法,控制台输出如下:
User{id=41, username='王一', birthday=Tue Dec 27 17:47:08 CST 2011, sex='男', address='北京'}
Role{roleId=1, roleName='院长', roleDesc='管理整个学院'}
Role{roleId=2, roleName='总裁', roleDesc='管理整个公司'}
User{id=45, username='Max', birthday=Tue May 04 12:04:06 CST 2010, sex='男', address='西宁'}
Role{roleId=1, roleName='院长', roleDesc='管理整个学院'}
User{id=42, username='王二', birthday=Sat Mar 12 15:09:37 CST 2011, sex='女', address='上海'}
User{id=43, username='老李', birthday=Wed Mar 14 11:34:34 CST 2012, sex='女', address='天津'}
User{id=46, username='老王', birthday=Sat Aug 07 17:37:26 CST 1999, sex='女', address='拉萨'}
User{id=48, username='John', birthday=Mon Jan 08 11:44:00 CST 1990, sex='女', address='广州'}
User{id=50, username='Lucy', birthday=Wed Dec 03 20:09:32 CST 2008, sex='m', address='哈尔滨'}
User{id=58, username='张三', birthday=Fri May 15 18:50:04 CST 2020, sex='男', address='南昌'}
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Github:https://github.com/codeaction