mybatisplus之Wrappers.ne踩坑记录解决

Classroom classroom = this.getOne(  
Wrappers.<Classroom>lambdaQuery()  
.select(Classroom::getId, Classroom::getJoinType)  
.eq(Classroom::getClassId, signupSubmitVO.getClassId())  
.eq(Classroom::getUserId, userId)  
);  
if (joinType == null && classroom != null) {  
joinType = classroom.getJoinType();  
}  
List<Classroom> hasClassroomList = this.list(  
Wrappers.<Classroom>lambdaQuery()  
.select(Classroom::getId, Classroom::getProvinceId, Classroom::getCityId, Classroom::getAreaId)  
.eq(Classroom::getClassId, signupSubmitVO.getClassId())  
.ne(classroom != null, Classroom::getId, classroom.getId())  //空指针
);

default Children ne(R column, Object val) {
    return this.ne(true, column, val);
}

Classroom classroom = this.getOne(
      Wrappers.<Classroom>lambdaQuery()
            .select(Classroom::getId, Classroom::getJoinType)
            .eq(Classroom::getClassId, signupSubmitVO.getClassId())
            .eq(Classroom::getUserId, userId)
);
if (joinType == null && classroom != null) {
   joinType = classroom.getJoinType();
}
LambdaQueryWrapper<Classroom> query = Wrappers.<Classroom>lambdaQuery()
      .select(Classroom::getId, Classroom::getProvinceId, Classroom::getCityId, Classroom::getAreaId)
      .eq(Classroom::getClassId, signupSubmitVO.getClassId())
if (classroom != null) {
   query.ne(Classroom::getId, classroom.getId());
}