记录下MybatisPlus的简单的增删改查

接口概述

Service和Mapper区别

Mapper简化了单表的sql操作步骤（CRUD），而Serivce则是对Mapper的功能增强。
Service虽然加入了数据库的操作，但还是以业务功能为主，而更加复杂的SQL查询，还是要靠Mapper对应的XML文件里去编写SQL语句

常用增删改查

查询所有数据

   /*** 查询所有数据*/@GetMapping("/getUserList")public List<TrainUserEntity> getUserList() {return trainUserService.list();}

根据id查询

  /*** 根据id查询数据*/@GetMapping("/getUserById")public TrainUserEntity getUserById(@RequestParam String id) {return trainUserService.getById(id);}

根据条件查询

   /*** 使用LambdaQueryWrapper查询指定年龄的人员*/@Overridepublic List<TrainUserEntity> getUserByAge(String age) {LambdaQueryWrapper<TrainUserEntity> userEntityLambdaQueryWrapper = new LambdaQueryWrapper<>();userEntityLambdaQueryWrapper.eq(TrainUserEntity::getAge, age);List<TrainUserEntity> list = trainUserMapper.selectList(userEntityLambdaQueryWrapper);return list;}

使用exists查询

查询有所属部门的人员

  public List<TrainUserEntity> getUserInfo() {LambdaQueryWrapper<TrainUserEntity> wrapper = new LambdaQueryWrapper<>();wrapper.exists("SELECT 1 FROM DEPT WHERE DEPT.DID = USER.DEPTID");List<TrainUserEntity> userVOList = trainMapper.selectList(wrapper);return userVOList;}

生成的SQL：

SELECT id,name,age,address,deptid FROM user WHERE (EXISTS (SELECT 1 FROM DEPT WHERE DEPT.DID = USER.DEPTID))

使用xml查询

新增

    /*** 新增** @param trainUserEntity 需要插入的数据* @return 是否成功*/@PostMapping("/saveUser")public boolean saveUser(@RequestBody TrainUserEntity trainUserEntity) {return trainService.save(trainUserEntity);}

   /*** 新增数据*/@Overridepublic boolean add(TrainUserEntity trainUserEntity) {return trainMapper.add(trainUserEntity);}

删除

    /*** 根据主键id删除一条数据** @param id 主键id* @return 是否成功*/@PostMapping("/removeById")public boolean deleteById(@RequestParam String id) {return trainService.removeById(id);}

  /*** 根据主键id删除一条数据** @param id 主键id* @return 删除数据的条数*/@Overridepublic int deleteById(String id) {LambdaQueryWrapper<TrainUserEntity> userEntityLambdaQueryWrapper = new LambdaQueryWrapper<>();userEntityLambdaQueryWrapper.eq(TrainUserEntity::getId, id);int result = trainMapper.delete(userEntityLambdaQueryWrapper);return result;}

修改

   /*** id修改一条数据** @param trainUserEntity 需要修改的数据* @return 修改结果*/@PostMapping("/updateUser")public boolean updateUser(@RequestBody TrainUserEntity trainUserEntity) {return trainService.updateById(trainUserEntity);}

    /*** 根据id更新实体数据*/@Overridepublic int modifyById(TrainUserEntity trainUserEntity) {LambdaUpdateWrapper<TrainUserEntity> updateWrapper = new LambdaUpdateWrapper<>();updateWrapper.eq(TrainUserEntity::getId, trainUserEntity.getId()).set(TrainUserEntity::getName, trainUserEntity.getName()).set(TrainUserEntity::getAddress, trainUserEntity.getAddress());int result = trainMapper.update(null, updateWrapper);return result;}