Mybatis Plus一对多联表查询及分页解决方案
文章目录
-
- 需求
- 需求分析
- 分页问题说明
- 分页问题原因
- 一对多场景一
- 一对多场景二
- 性能优化
-
- 优化解决方案
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 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