mybatis-plus自带QueryWrapper自定义sql实现复杂查询实例详解

2022-11-13 18:11:03 mybatis

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<xxxDO> queryWrapper = Wrappers.lambdaQuery();
    queryWrapper.select(xxxDO::getName, DO::getId);
    queryWrapper.eq(xxxDO::getDeleteFlag, 0);
    queryWrapper.eq(xxxDO::getStatus, 0);
    queryWrapper.groupBy(xxxDO::getName);
    List<xxxDO> 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<xxxDO> queryWrapper = new QueryWrapper<xxxDO>()
            .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<Map<String, Object>> mapList = getBaseMapper().selectMaps(queryWrapper);
    Map<String, String> reGISterNumMap = new HashMap<>(mapList.size());
    for (Map<String, Object> 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<Entity> buildPage = new Page<>(0, 200);
        // ServiceImpl的page调用的是baseMapper的selectPage, getBaseMapper().selectPage()
        IPage<Entity> page = page(buildPage, queryWrapper);

sql打印

补充：Mybatis-Plus QueryWrapper +sql自定义查询

一： 需要自定义的QueryWrapper查询工具类，定义查询规则

public static final String SQL_RULES_COLUMN = "SQL_RULES_COLUMN";

private static final String BEGIN = "_begin";  // 字段范围查询开始标识
private static final String END = "_end";  // 字段范围查询结束标识
private static final String STAR = "*";  // 字段模糊查询标识
private static final String COMMA = ",";
private static final String NOT_EQUAL = "!";

二： 正常的QueryWrapper查询，在mapper文件中使用 @Param(Constants.WRAPPER)

    List<Emdj> listAll(IPage<Emdj> page, @Param(Constants.WRAPPER) QueryWrapper<Emdj> queryWrapper);

        xml文件中使用ew.customSqlSegment，<where>标签可以不加

   <select id="listAll" resultType="net.zazn.modules.discipline.entity.Emdj">
       select id,lffh,xm,jsh,szrq,emlx,spzt,gjmj,flag,jlzt
       from emdj
       <where>${ew.customSqlSegment}</where>
   </select>

总结

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