mybatis-plus 自带QueryWrapper自定义sql实现复杂查询

目录

常用写法

自定义sql

补充: 查询条件中使用函数apply

补充: 末尾sql追加last

补充:排序

补充:or查询


常用写法

xxxDO=实体类, 相当于:

select name, id from xxx group by name where delete_flag = 0 and status = 0

    LambdaQueryWrapper queryWrapper = Wrappers.lambdaQuery();
    queryWrapper.select(xxxDO::getName, DO::getId);
    queryWrapper.eq(xxxDO::getDeleteFlag, 0);
    queryWrapper.eq(xxxDO::getStatus, 0);
    queryWrapper.groupBy(xxxDO::getName);
    List list = getBaseMapper().selectList(queryWrapper);

自定义sql

xxxDO=实体类,相当于:

select sex, ifnull(count(id), 0) AS num, CASE WHEN sex = 1 THEN '男' WHEN sex = 0 THEN '女' ELSE '未知' END AS sexStr from xxx group by sex where status = 0

    LambdaQueryWrapper queryWrapper = new QueryWrapper()
            .select("sex, ifnull(count(id), 0) AS num, CASE WHEN sex = 1 THEN '男' WHEN sex = 0 THEN '女' ELSE '未知' END AS sexStr").lambda();
    queryWrapper.eq(xxxDO::getStatus, 0);
    queryWrapper.groupBy(xxxDO::getSex);
    List> mapList = getBaseMapper().selectMaps(queryWrapper);
    Map registerNumMap = new HashMap<>(mapList.size());
    for (Map map : mapList) {
        String key = String.valueOf(map.get("sexStr"));
        String num = String.valueOf(map.get("num"));
        registerNumMap.put(key, num);
    }

返回结果是一个list, 里面的map key是查询的属性名, value是参数值。伪代码示意:

list[0]

        map[0] (sex=1)

        map[1] (num=5)

        map[2] (sexStr=男)

list[1]

        map[0] (sex=1)

        map[1] (num=5)

        map[2] (sexStr=男)

偶然而发, 记录一下

补充: 查询条件中使用函数apply

    queryWrapper.apply("INET_ATON(qsip) <= INET_ATON({0})", ipQuery);
    queryWrapper.apply("INET_ATON(zzip) >= INET_ATON({0})", ipQuery);

补充: 末尾sql追加last

        queryWrapper.last(" order by id asc");
        queryWrapper.last("limit 1");

补充:排序

        // last也可以追加limit 这里用page接口

        IPage buildPage = new Page<>(0, 200);
        // ServiceImpl的page调用的是baseMapper的selectPage, getBaseMapper().selectPage()
        IPage page = page(buildPage, queryWrapper);

sql打印

补充:or查询

        LambdaQueryWrapper queryWrapper = Wrappers.lambdaQuery();
        queryWrapper.select(Entity::getCode);
        queryWrapper.eq(Entity::getAge, 10);
        queryWrapper.and(w -> w.eq(Entity::getName, "张三").or().eq(Entity::getName2, "张三"));
        List list = service.list(queryWrapper);


打印sql如下
SELECT code FROM table WHERE (age = ? AND (name = ? OR name2 = ? ))
==> Parameters: 10(Integer), 张三(String), 张三(String)

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