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User Likes

Use one Set of user IDs per article so repeat likes from the same user do not increase the count.

Data Structure​

Key demo:likes:article:a1001 contains Set members such as u1001 and u1002.

Mapping​

Read members directly as List<String>, without an entity. Sets are unordered; SISMEMBER returns RESULT as 0 or 1.

Mapper​

ArticleLikeMapper.java
package com.example.redis;

import java.util.List;
import net.hasor.dbvisitor.mapper.Delete;
import net.hasor.dbvisitor.mapper.Insert;
import net.hasor.dbvisitor.mapper.Param;
import net.hasor.dbvisitor.mapper.Query;
import net.hasor.dbvisitor.mapper.SimpleMapper;

@SimpleMapper
public interface ArticleLikeMapper {
    @Insert("SADD #{key} #{userId}")
    int like(@Param("key") String key, @Param("userId") String userId);

    @Delete("SREM #{key} #{userId}")
    int unlike(@Param("key") String key, @Param("userId") String userId);

    @Query("SISMEMBER #{key} #{userId}")
    long contains(@Param("key") String key, @Param("userId") String userId);

    @Query("SCARD #{key}")
    long count(@Param("key") String key);

    @Query("SMEMBERS #{key}")
    List<String> users(@Param("key") String key);
}

Calling the Mapper​

Run inside the Session created above:

ArticleLikeMapper mapper = session.createMapper(ArticleLikeMapper.class);
String key = "demo:likes:article:a1001";

int first = mapper.like(key, "u1001");
int repeated = mapper.like(key, "u1001");
mapper.like(key, "u1002");
long count = mapper.count(key);
long liked = mapper.contains(key, "u1001");
List<String> users = mapper.users(key);
int removed = mapper.unlike(key, "u1001");

Starting with an empty set, first = 1, repeated = 0, count = 2, liked = 1 and removed = 1. users contains u1001 and u1002 in no guaranteed order.

Notes​

  • A repeat like returns 0, not an error; removing an absent like also returns 0.
  • Use count for the number of likes instead of fetching every member of a large set.