Mybatis Plus一对多联表查询及分页解决方案

需求

查询用户信息列表，其中包含用户对应角色信息，页面检索条件有根据角色名称查询用户列表；

需求分析

一个用户对应多个角色，用户信息和角色信息分表根据用户id关联存储，用户和角色一对多进行表连接查询，

创建对应表：

CREATE TABLE `sys_user` (
  `id` bigint NOT NULL AUTO_INCREMENT COMMENT '用户ID',
  `name` varchar(50) DEFAULT NULL COMMENT '姓名',
  `age` int DEFAULT NULL COMMENT '年龄',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE=InnoDB  DEFAULT CHARSET=utf8mb4  COMMENT='用户信息表';

CREATE TABLE `sys_role` (
  `id` bigint NOT NULL AUTO_INCREMENT COMMENT '角色ID',
  `role_name` varchar(30) NOT NULL COMMENT '角色名称',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8mb4  COMMENT='角色信息表';


CREATE TABLE `sys_user_role` (
  `id` bigint NOT NULL AUTO_INCREMENT COMMENT 'ID',
  `user_id` bigint NOT NULL COMMENT '用户ID',
  `role_id` bigint NOT NULL COMMENT '角色ID',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4  COMMENT='用户和角色关联表';


INSERT INTO tsq.sys_user (name,age) VALUES
	 ('张三',18),
	 ('王二',19);

INSERT INTO tsq.sys_role (role_name) VALUES
	 ('角色1'),
	 ('角色2'),
	 ('角色3'),
	 ('角色4');

INSERT INTO tsq.sys_user_role (user_id,role_id) VALUES
	 (1,1),
	 (1,2),
	 (1,3),
	 (2,4);

对应实体类：

@Data
@ApiModel("用户信息表")
@TableName("sys_user")
public class User implements Serializable {

    private static final long serialVersionUID = 1L;
    
    @ApiModelProperty("用户id")
    private Long id;
    @ApiModelProperty("姓名")
    private String name;
    @ApiModelProperty("年龄")
    private Integer age;
}


@Data
@ApiModel("角色信息表")
@TableName("sys_role")
public class Role implements Serializable {

    private static final long serialVersionUID = 1L;
    
    @ApiModelProperty("角色id")
    private Long id;
    @ApiModelProperty("角色名称")
    private String roleName;
}



@Data
@ApiModel("用户信息表")
public class UserVo implements Serializable {

    private static final long serialVersionUID = 1L;

    @ApiModelProperty("用户id")
    private Long id;
    @ApiModelProperty("姓名")
    private String name;
    @ApiModelProperty("年龄")
    private Integer age;
    
    private List<Role> roleList;

}

分页问题说明

在使用一对多连接查询并且分页时，发现返回的分页列表数据数量不对
比如这里查询用户对应角色列表，如果使用直接映射，那么 roleList 的每个 Role 对象都会算一条数据；比如查第一页，一个用户有三个角色每页三条数据，就会出现查出一个 User ，三个 Role 的这些情况，这它也算每页三条（其实就只查到一个用户）

分页问题原因

mybatis-plus一对多分页时，应该使用子查询的映射方式，使用直接映射就会出错
所以直接映射适用于一对一，子查询映射使用于一对多；

一对多场景一

查询用户表的内容，角色表不参与条件查询，用懒加载形式

// controller
  @GetMapping("/pageList")
	public Map<String, Object> pageList(@RequestParam(required = false, defaultValue = "0") int offset,
	                                    @RequestParam(required = false, defaultValue = "10") int pagesize) {
		return userService.pageList(offset, pagesize);
	}
  
  
// serviceimpl
  @Override
	public Map<String, Object> pageList(int offset, int pagesize) {
      List<UserVo> pageList = userMapper.pageList(offset, pagesize);
      int totalCount = userMapper.pageListCount();
      Map<String, Object> result = new HashMap<String, Object>();
      result.put("pageList", pageList);
      result.put("totalCount", totalCount);

      return result;
	}
  
// mapper.xml

   <resultMap id="getUserInfo" type="com.tsq.democase.onetomany.domain.vo.UserVo" >
        <result column="id" property="id" />
        <result column="name" property="name" />
        <result column="age" property="age" />
        <collection property="roleList" javaType="ArrayList" ofType="com.tsq.democase.onetomany.domain.Role"
                    select="getRolesByUserId" column="{userId = id}"/>
    </resultMap>

    <select id="getRolesByUserId" resultType="com.tsq.democase.onetomany.domain.Role">
        SELECT *
        FROM sys_user_role ur
                 inner join sys_role r on ur.role_id = r.id
        where ur.user_id = #{userId}
    </select>
    
    <select id="pageList"  resultMap="getUserInfo">
        SELECT *
        FROM sys_user
        LIMIT #{offset}, #{pageSize}
    </select>
    
    <select id="pageListCount" resultType="java.lang.Integer">
        SELECT count(1)
        FROM sys_user
    </select>

查询结果

一对多场景二

查询用户表的内容，角色表要作为查询条件参与查询，例如要根据角色名称查询出用户列表

// controller
	@GetMapping("/pageListByRoleName")
	public Map<String, Object> pageListByRoleName(@RequestParam(required = false, defaultValue = "0") int offset,
	                                    @RequestParam(required = false, defaultValue = "10") int pagesize,
	                                    @RequestParam String roleName) {
		return userService.pageListByRoleName(offset, pagesize, roleName);
	}
  
  
// serviceimpl
	@Override
	public Map<String, Object> pageListByRoleName(int offset, int pagesize,String roleName) {
      List<UserVo> pageList = userMapper.pageListByRoleName(offset, pagesize, roleName);
      int totalCount = userMapper.pageListCount();
      Map<String, Object> result = new HashMap<String, Object>();
      result.put("pageList", pageList);
      result.put("totalCount", totalCount);

      return result;
	}
  
// mapper.xml
   <resultMap id="getUserInfoByRoleName" type="com.tsq.democase.onetomany.domain.vo.UserVo" >
        <result column="id" property="id" />
        <result column="name" property="name" />
        <result column="age" property="age" />
        <collection property="roleList" javaType="ArrayList" ofType="com.tsq.democase.onetomany.domain.Role"
                    select="getRolesByUserIdAndRoleName" column="{userId = id,roleName = roleName}"/>
    </resultMap>

    <select id="getRolesByUserIdAndRoleName" resultType="com.tsq.democase.onetomany.domain.Role">
        SELECT *
        FROM sys_user_role ur
        inner join sys_role r on ur.role_id = r.id
        where ur.user_id = #{userId}
        <if test="roleName != null and roleName != ''" >
            and r.role_name LIKE concat('%', #{roleName}, '%')
        </if>
    </select>

    <select id="pageListByRoleName"  resultMap="getUserInfoByRoleName">
        SELECT temp.* FROM (
        SELECT distinct u.*,#{roleName} as roleName
        FROM sys_user u
        left join sys_user_role ur on u.id = ur.user_id
        left join sys_role r on r.id = ur.role_id
        <where>
            <if test="roleName != null and roleName != ''" >
                r.role_name LIKE concat('%', #{roleName}, '%')
            </if>
        </where>
        ) temp
        LIMIT #{offset}, #{pageSize}
    </select>

查询结果

性能优化

原因：

场景一二中使用 select方式会触发多次子查询（SELECT *FROM sys_user_role ur inner join sys_role …），当数据量大时会使查询速度很慢。

场景二中查询时产生的sql日志如下：

--  ==>  
SELECT
    temp.* 
FROM
    ( SELECT
        distinct u.*,
        '角色' as roleName 
    FROM
        sys_user u 
    left join
        sys_user_role ur 
            on u.id = ur.user_id 
    left join
        sys_role r 
            on r.id = ur.role_id 
    WHERE
        r.role_name LIKE concat('%', '角色', '%') ) temp LIMIT 0,
    10 
 --  ====>  
SELECT
    * 
FROM
    sys_user_role ur 
inner join
    sys_role r 
        on ur.role_id = r.id 
where
    ur.user_id = 1 
    and r.role_name LIKE concat('%', '角色', '%') 
 --  ====>  
SELECT
    * 
FROM
    sys_user_role ur 
inner join
    sys_role r 
        on ur.role_id = r.id 
where
    ur.user_id = 2 
    and r.role_name LIKE concat('%', '角色', '%') 
 --  ==>  
SELECT
    count(1) 
FROM
    sys_user 

sql可见如果有100各用户就要执行一百次子查询，效率极低。

优化解决方案

sql中只查询sys_user相关信息并且做roleName 过滤，roleList在java代码中用stream关联role并赋值roleList；

// serviceimpl
  @Override
  public Map<String, Object> pageListByRoleName(int offset, int pagesize,String roleName) {
     // List<UserVo> pageList = userMapper.pageListByRoleName(offset, pagesize, roleName);
     List<UserVo> pageList = userMapper.pageListByRoleName2(offset, pagesize, roleName);
     List<Long> userIds = pageList.stream().map(UserVo::getId).collect(Collectors.toList());
     List<UserRoleVo> userRoleVos =  userMapper.getUserRoleByUserIds(userIds);
     Map<Long, List<UserRoleVo>> userRoleMap = userRoleVos.stream().collect(Collectors.groupingBy(UserRoleVo::getUserId, Collectors.toList()));
     pageList.forEach(u -> {
        List<UserRoleVo> roleVos = userRoleMap.get(u.getId());
        List<RoleVo> roles = BeanUtils.listCopy(roleVos, CopyOptions.create(), RoleVo.class);
        u.setRoleList(roles);
     });
     int totalCount = userMapper.pageListCount();
     Map<String, Object> result = new HashMap<String, Object>();
     result.put("pageList", pageList);
     result.put("totalCount", totalCount);

     return result;
  }

// mapper.xml
<select id="pageListByRoleName2"  resultType="com.tsq.democase.onetomany.domain.vo.UserVo">
    SELECT distinct u.*
    FROM sys_user u
    left join sys_user_role ur on u.id = ur.user_id
    left join sys_role r on r.id = ur.role_id
    <where>
        <if test="roleName != null and roleName != ''" >
            r.role_name LIKE concat('%', #{roleName}, '%')
        </if>
    </where>
    LIMIT #{offset}, #{pageSize}
</select>  

查询结果

同场景二。

查询时产生的sql如下：

  --  ==>  
  SELECT
      distinct u.* 
  FROM
      sys_user u 
  left join
      sys_user_role ur 
          on u.id = ur.user_id 
  left join
      sys_role r 
          on r.id = ur.role_id 
  WHERE
      r.role_name LIKE concat('%', '角色', '%') LIMIT 0, 10 
   --  ==>  
  SELECT
      ur.user_id ,
      r.id roleId,
      r.role_name 
  FROM
      sys_user_role ur 
  inner join
      sys_role r 
          on ur.role_id = r.id 
   --  ==>  
  SELECT
      count(1) 
  FROM
      sys_user 
 

由sql日志可见这种方式比纯sql方式效率高一些文章来源地址https://www.toymoban.com/news/detail-410435.html

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