阿超 > mybatis-plus随机查询工具类

mybatis-plus随机查询工具类

2021-05-17

java

作为一个人，对父母要尊敬，对子女要慈爱，对穷亲戚要慷慨，对一切人要有礼貌。——(美国)罗素

都封装好了

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/**
 * 随机取几条
 *
 * @param function 表名::列名
 * @return T
 * @author <achao1441470436@gmail.com>
 * @since 2021/5/17 0017 10:34
 */
@SuppressWarnings("unchecked")
public static <T, O> List<O> getAny(SFunction<O, T> function, Integer limit) {
    SerializedLambda lambda = Optional.ofNullable(function).map(LambdaUtils::resolve).orElseThrow(() -> ExceptionUtils.mpe("传入条件不能为空"));
    Class<O> entityClass = (Class<O>) lambda.getImplClass();
    TableInfo tableInfo = Optional.ofNullable(entityClass).map(TableInfoHelper::getTableInfo).orElseThrow(() -> ExceptionUtils.mpe("未找到该实体类对应BaseMapper，请注入对应mybatis-plus的BaseMapper"));
    String tableName = tableInfo.getTableName();
    String id = PropertyNamer.methodToProperty(lambda.getImplMethodName());
    List<HashMap<String, Object>> mapList = (List<HashMap<String, Object>>) USER_MAPPER.getAny(tableName, id, limit, entityClass);
    List<TableFieldInfo> fieldList = tableInfo.getFieldList();
    Reflector reflector = new Reflector(entityClass);
    Map<String, Invoker> columnSetterMap = fieldList.parallelStream().collect(Collectors.toMap(tbf -> Optional.ofNullable(tbf).map(TableFieldInfo::getField).map(field -> field.getAnnotation(TableField.class)).map(TableField::value).filter(StringUtils::isNotBlank).orElse(Objects.requireNonNull(tbf).getProperty()), f -> reflector.getSetInvoker(f.getProperty()), (v1, v2) -> v2));
    return mapList.stream().map(map -> {
        O bean = ClassUtils.newInstance(entityClass);
        map.forEach((key, value) -> Optional.ofNullable(key).map(columnSetterMap::get).ifPresent(i -> {
            try {
                i.invoke(bean, new Object[]{value});
            } catch (IllegalAccessException | InvocationTargetException e) {
                e.printStackTrace();
            }
        }));
        return bean;
    }).collect(Collectors.toList());
}

/**
 * 随机取一条
 *
 * @param function 表名::列名
 * @return O 随便取的
 * @author <achao1441470436@gmail.com>
 * @since 2021/5/17 0017 12:29
 */
public static <O> O getAnyOne(SFunction<O, ?> function) {
    return getAny(function, 1).parallelStream().findAny().orElse(null);
}

这里的USER_MAPPER我们可以使用任意一个mapper，我这里使用的是静态注入的方式

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private static final UserMapper USER_MAPPER = SpringContextHolder.getBean(UserMapper.class);

然后是mapper里的方法

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/**
 * 随机取一条
 *
 * @param tableName  表名
 * @param columnName 列名
 * @param limit      取几条
 * @return O
 * @author <achao1441470436@gmail.com>
 * @since 2021/5/17 0017 10:47
 */
<O> List<O> getAny(@Param("table_name") String tableName, @Param("id") String columnName, @Param("limit") Integer limit, Class<O> type);

以及对应的xml

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<!--  随机取一条  -->
<select id="getAny" resultType="java.util.Map">
    SELECT *
    FROM ${table_name} AS t1 JOIN (SELECT ROUND(RAND() *((SELECT MAX(${id}) FROM ${table_name}) - (SELECT MIN(${id}) FROM ${table_name})) +(SELECT MIN(${id}) FROM ${table_name})) AS tmp_id) AS t2
    WHERE t1.${id} >= t2.tmp_id
    ORDER BY t1.${id} LIMIT #{limit};
</select>

实际使用场景、方式

image-20210517222647624