MyBatisPlus之DQL编程控制

//方式一：按条件查询
    QueryWrapper qw = new QueryWrapper();
    //小于3
    qw.lt("id",3);
    List userList = userDao.selectList(qw);
    System.out.println(userList);

QueryWrapper qw = new QueryWrapper();
    //小于3大于1
    qw.lt("id",3).gt("id",1);
    List userList = userDao.selectList(qw);
    System.out.println(userList);

//方式三：lambda格式按条件查询
    LambdaQueryWrapper<User> lwq = new LambdaQueryWrapper<>();
    //id为1到3之间
    lwq.lt(User::getId,3);
    lwq.gt(User::getId,1);
    //id为小于2或者大于3
    //链式查询
    lwq.lt(User::getId,2).or().gt(User::getId,3);
    List userList = userDao.selectList(lwq);
    System.out.println(userList);

qw.lt("id",3).gt("id",1);

lwq.lt(User::getId,2).or().gt(User::getId,3);

UserQuery uq = new UserQuery();
    uq.setId(1);
    uq.setId2(3);
    //null判定
    LambdaQueryWrapper<User> lqw = new LambdaQueryWrapper<>();
    if(null != uq.getId()) {
      lqw.lt(User::getId,uq.getId2());
    }
    if(null != uq.getId2()) {
      lqw.gt(User::getId,uq.getId());
    }
    List<User> userList = userDao.selectList(lqw);
    System.out.println(userList);

//先判定第一个参数是否为true,如果为true,连接当前条件
    UserQuery uq = new UserQuery();
    uq.setId(1);
    uq.setId2(3);
    //null判定
    LambdaQueryWrapper<User> lqw = new LambdaQueryWrapper<>();
    lqw.gt(null!=uq.getId2(), User::getId, uq.getId())
    lqw.lt(null!= uq.getId(),User::getId,uq.getId2());
    List<User> userList = userDao.selectList(lqw);
    System.out.println(userList);

//先判定第一个参数是否为true,如果为true,连接当前条件
    UserQuery uq = new UserQuery();
    uq.setId(1);
    uq.setId2(3);
    //null判定
    LambdaQueryWrapper<User> lqw = new LambdaQueryWrapper<>();
    lqw.gt(null!=uq.getId2(), User::getId, uq.getId())
          .lt(null!= uq.getId(),User::getId,uq.getId2());
    List<User> userList = userDao.selectList(lqw);
    System.out.println(userList);

LambdaQueryWrapper<User> lqw = new LambdaQueryWrapper<>();
    lqw.select(User::getId,User::getAddr);
    List<User> userList = userDao.selectList(lqw);
    System.out.println(userList);

QueryWrapper<User> qw = new QueryWrapper<>();
    qw.select("count(*) as count");
    qw.groupBy("gender");
    List<Map<String, Object>> userList = userDao.selectMaps(qw);
    System.out.println(userList);