Java框架_Mybatis_day07_多表查询之多对多查询

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原创最新推荐文章于 2026-09-05 12:34:21 发布 282 阅读 AI 写同款· GEO 优化 ›

mybatis多表联查(一对一、一对多/多对一、多对多) 在开发过程中单表查询往往不能满足需求分析的很多功能，对于比较复杂业务来说，关联的表有几个，甚至是几十个并且表与表之间的关联相当复杂。为了能够实现复杂的功能业务，就必须进行多表查询，在mybatis中提供了多表查询映射标签，可以实现表之间的一对一、一对多、多对多关系的映射。 **注意：**大批代码正在向你靠近注意：测试代码块放最后运行出错可以看看在示例演练之前需要的准备：首先创建一个maven项目在pom.xml中配置文件创建配置jdbc.properties 创建配置文件config.xml连接数据库和数阅读详情

十一、Mybatis 多表查询之多对多查询

11.1 准备工作

11.1.1 角色表

11.1.2 Role.java

11.2 多对多查询，查询角色同时关联用户

11.3 多对多查询，查询用户同时关联角色

十一、Mybatis 多表查询之多对多查询

11.1 准备工作

这里我们新建一个角色表（role），并且创建 Role.java 、RoleDao.xml 等文件。

11.1.1 角色表

DROP TABLE IF EXISTS `role`;
CREATE TABLE `role` (
  `ID` int(11) NOT NULL COMMENT '编号',
  `ROLE_NAME` varchar(30) default NULL COMMENT '角色名称',
  `ROLE_DESC` varchar(60) default NULL COMMENT '角色描述',
  PRIMARY KEY  (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

insert  into `role`(`ID`,`ROLE_NAME`,`ROLE_DESC`) values (1,'院长','管理整个学院'),(2,'总裁','管理整个公司'),(3,'校长','管理整个学校');

DROP TABLE IF EXISTS `user_role`;

CREATE TABLE `user_role` (
  `UID` int(11) NOT NULL COMMENT '用户编号',
  `RID` int(11) NOT NULL COMMENT '角色编号',
  PRIMARY KEY  (`UID`,`RID`),
  KEY `FK_Reference_10` (`RID`),
  CONSTRAINT `FK_Reference_10` FOREIGN KEY (`RID`) REFERENCES `role` (`ID`),
  CONSTRAINT `FK_Reference_9` FOREIGN KEY (`UID`) REFERENCES `user` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

insert  into `user_role`(`UID`,`RID`) values (41,1),(48,1),(41,2);

11.1.2 Role.java

package com.cpz.domain;

import java.util.ArrayList;
import java.util.List;

public class Role {
    private Integer id;
    private String roleName;
    private String roleDesc;
   
    @Override
    public String toString() {
        return "Role{" +
                "id=" + id +
                ", roleName='" + roleName + '\'' +
                ", roleDesc='" + roleDesc + '\'' +
                '}';
    }


    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    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;
    }
}

11.2 多对多查询，查询角色同时关联用户

修改Role.java

package com.cpz.domain;

import java.util.ArrayList;
import java.util.List;

public class Role {
    private Integer id;
    private String roleName;
    private String roleDesc;
    private List<User> users = new ArrayList<User>();

    @Override
    public String toString() {
        return "Role{" +
                "id=" + id +
                ", roleName='" + roleName + '\'' +
                ", roleDesc='" + roleDesc + '\'' +
                ", users=" + users +
                '}';
    }

    public List<User> getUsers() {
        return users;
    }

    public void setUsers(List<User> users) {
        this.users = users;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    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;
    }
}

RoleDao.java

package com.cpz.dao;

import com.cpz.domain.Role;

import java.util.List;

public interface RoleDao {
    public List<Role> findRoleUser();
}

RoleDao.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="com.cpz.dao.RoleDao">

    <resultMap id="roleUserMap" type="role">
        <id column="rid" property="id"></id>
        <result column="role_name" property="roleName"></result>
        <result column="role_desc" property="roleDesc"></result>
        <collection property="users" ofType="user">
            <id column="id" property="id"></id>
            <result column="username" property="username"></result>
            <result column="birthday" property="birthday"></result>
            <result column="sex" property="sex"></result>
            <result column="address" property="address"></result>
        </collection>
    </resultMap>

    <select id="findRoleUser" resultMap="roleUserMap">
          SELECT u.*,r.id rid,r.role_name,r.role_desc FROM role r LEFT JOIN user_role ur ON r.id = ur.rid LEFT JOIN USER u ON ur.uid = u.id
    </select>
</mapper>

注意：sql语句如果有换行，需要在sql的后面尽量加一个空格

TestUser.java

    @Test
    public void findRoleUser(){
        List<Role> list = roleDao.findRoleUser();
        for (Role role : list) {
            System.out.println(role);
        }
    }

11.3 多对多查询，查询用户同时关联角色

User.java

package com.cpz.domain;

import java.util.ArrayList;
import java.util.Date;
import java.util.List;

public class User {
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;
    private List<Role> roles = new ArrayList<Role>();

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", birthday=" + birthday +
                ", sex='" + sex + '\'' +
                ", address='" + address + '\'' +
                ", roles=" + 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;
    }

}

UserDao.java

package com.cpz.dao;

import com.cpz.domain.User;

import java.util.List;

public interface UserDao {
    public List<User> findUserRole();
}

UserDao.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="com.cpz.dao.UserDao">

    <resultMap id="userRoleMap" type="user">
        <id column="id" property="id"></id>
        <result column="username" property="username"></result>
        <result column="birthday" property="birthday"></result>
        <result column="sex" property="sex"></result>
        <result column="address" property="address"></result>
        <collection property="roles" ofType="role">
            <id column="rid" property="id"></id>
            <result column="role_name" property="roleName"></result>
            <result column="role_desc" property="roleDesc"></result>
        </collection>
    </resultMap>

    <select id="findUserRole" resultMap="userRoleMap">
         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>

TestUser.java

    @Test
    public void findUserRole(){
        List<User> list = userDao.findUserRole();
        for (User user : list) {
            System.out.println(user);
        }
    }

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