伙伴匹配系统踩坑 - 编程导航 | 一线开发者编程经验和技术实战分享

首先自我介绍，我是一名刚加入星球一个多月的前端同学，今年专升本大四，目标秋招找到一份前端的工作，最近在跟着鱼皮哥做伙伴匹配系统，后端是下载的鱼皮哥仓库里的，然后做到了队伍搜索那里发现搜索数据库中没有的队伍时报sql错误：

Resolved [org.springframework.jdbc.BadSqlGrammarException: <EOL><EOL>### Error querying database. Cause: java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '))' at line 4<EOL><EOL>### The error may exist in com/yupi/yupao/mapper/UserTeamMapper.java (best guess)<EOL><EOL>### The error may involve defaultParameterMap<EOL><EOL>### The error occurred while setting parameters<EOL><EOL>### SQL: SELECT id,userId,teamId,joinTime,createTime,updateTime,isDelete FROM user_team WHERE isDelete=0 AND (teamId IN ())<EOL><EOL>### Cause: java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '))' at line 4<EOL>; bad SQL grammar []; nested exception is java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '))' at line 4]

然后按着报错进后端找UserTeamMapper.java，这里是写了接口继承了mybatisplus中的BaseMapper没有错误，这我可就犯难了mybatisplus不是不用写sql语句吗哪来的sql报错，我一个前端菜鸡只了解一些基础的java语法，仅仅是把后端跑起来都用了我两天时间，我不会改啊（qaq），然后百度、问gpt都没能解决，急得我抓耳挠腮，我看着这个报错中的sql语句发现and后 teamId IN ()这里为空然后百度一下mybatisplus中 IN空相关问题发现是没有判空导致报错，这就好办了，加上判空（ if (CollectionUtils.isNotEmpty(teamList) ) ）再试试，果然加上判空就解决了，这个接口的完整代码：

@GetMapping("/list")

public BaseResponse<List<TeamUserVO>> listTeams(TeamQuery teamQuery, HttpServletRequest request) {

if (teamQuery == null) {

throw new BusinessException(ErrorCode.PARAMS_ERROR);

}

boolean isAdmin = userService.isAdmin(request);

// 1、查询队伍列表

List<TeamUserVO> teamList = teamService.listTeams(teamQuery, isAdmin);

if (CollectionUtils.isNotEmpty(teamList) ) {

final List<Long> teamIdList = teamList.stream().map(TeamUserVO::getId).collect(Collectors.toList());

// 2、判断当前用户是否已加入队伍

QueryWrapper<UserTeam> userTeamQueryWrapper = new QueryWrapper<>();

try {

User loginUser = userService.getLoginUser(request);

userTeamQueryWrapper.eq("userId", loginUser.getId());

userTeamQueryWrapper.in("teamId", teamIdList);

List<UserTeam> userTeamList = userTeamService.list(userTeamQueryWrapper);

// 已加入的队伍 id 集合

Set<Long> hasJoinTeamIdSet = userTeamList.stream().map(UserTeam::getTeamId).collect(Collectors.toSet());

teamList.forEach(team -> {

boolean hasJoin = hasJoinTeamIdSet.contains(team.getId());

team.setHasJoin(hasJoin);

});

} catch (Exception e) {

}

// 3、查询已加入队伍的人数

QueryWrapper<UserTeam> userTeamJoinQueryWrapper = new QueryWrapper<>();

userTeamJoinQueryWrapper.in("teamId", teamIdList);

List<UserTeam> userTeamList = userTeamService.list(userTeamJoinQueryWrapper);

// 队伍 id => 加入这个队伍的用户列表

Map<Long, List<UserTeam>> teamIdUserTeamList = userTeamList.stream().collect(Collectors.groupingBy(UserTeam::getTeamId));

teamList.forEach(team -> team.setHasJoinNum(teamIdUserTeamList.getOrDefault(team.getId(), new ArrayList<>()).size()));

}

return ResultUtils.success(teamList);

}