如果结果是 MultiBulk，如何从 RedisResult 中检索值

Question

我可以通过执行以下命令来检索 Redis 数据库中的所有键：

RedisResult allRedisKeys = redisDatabase.Execute("KEYS", new List<object>
{
   "*"
})

但我不能使用变量 allRedisKeys，因为它的 _value 字段是私有的。如何从 RedisResult 中提取值？在我的例子中，_value 拥有一个 RedisResult[]，而 allRedisKeys 的 RedisType 为 RedisType.MultiBulk。

Answer 1

首先，根据the documentation，不要在生产环境中使用KEYS 命令。但是，您可以在每个服务器上使用 .Keys 方法，但这需要单独查询每个服务器（而且它是 O(N)，所以也不是最好的）。

如需更快（但更复杂）的解决方案，请查看 Marc Gravell 的 this answer。基本上，您将所有密钥存储在一个 SET 中，因此您有 O(1) 响应时间。

这是我对他建议的实施：

/// <summary>
/// Class that keeps track of cache keys and the expiration of said keys. 
/// Uses a LIST to store the keys because it's faster than using SCAN on the entire Redis database.
/// Expirations are stored as ticks.
/// </summary>
public static class KeyAndExpirationTracker
{
    private const string ALL_KEYS = "ALL_KEYS";
    private const string EXPIRATION_SUFFIX = "|EXPIRATION";

    public static void StoreKeyAndExpiration(IDatabase db, string key, TimeSpan? timeToLive, ITransaction transaction)
    {
        string expiryKey = $"{key}{EXPIRATION_SUFFIX}";
        // although Redis will automatically replace an existing key, 
        // we still have to remove this in case this we went from having an expiration to not expiring
        db.KeyDelete(expiryKey);

        // add the item key to the list of keys
        transaction.SetAddAsync(key);
        // add the separate cache item for expiration (if necessary)
        if (timeToLive.HasValue)
        {
            DateTime expiry;
            try
            {
                expiry = DateTime.UtcNow.Add(timeToLive.Value);
                transaction.StringSetAsync(expiryKey, expiry.Ticks.ToString());
            }
            catch (ArgumentOutOfRangeException)
            {
                // no expiration then
            }
        }
    }

    public static void StoreKeyAndExpiration(IDatabase db, string key, DateTime? expiration, ITransaction transaction)
    {
        string expiryKey = $"{key}{EXPIRATION_SUFFIX}";
        // although Redis will automatically replace an existing key, we still have to remove this in case this we went from having an expiration to not expiring
        db.KeyDelete(expiryKey);

        // add the item key to the list of keys for this client type
        transaction.SetAddAsync(cacheKey, key);
        // add the separate cache item for expiration (if necessary)
        if (expiration.HasValue)
        {
            transaction.StringSetAsync(expiryKey, expiration.Value.Ticks.ToString());
        }
    }

    public static IEnumerable<string> GetKeys(IDatabase db)
    {
        RedisValue[] keys = db.SetMembers(ALL_KEYS));
        if (keys.Length == 0)
            return new string[0];

        List<string> expiredKeys = new List<string>(keys.Count());
        List<string> ret = new List<string>(keys.Count());

        // get expiration values using SORT with GET: https://redis.io/commands/sort
        RedisValue[] results = db.Sort(
            ALL_KEYS, 
            sortType: SortType.Alphabetic, 
            by: "notarealkey", // a (hopefully) non-existent key which causes the list to actually not be sorted
            get: new RedisValue[] { $"*{EXPIRATION_SUFFIX}", "#" } // # = "get the list item itself" which means the key in our case
        ));

        // SORT results will be in the same order as the GET parameters: 
        // result[0] = expiration (= null if no matching expiration item found)
        // result[1] = key
        // (repeat)
        for (int i = 0; i < results.Length; i += 2)
        {
            string key = results[i + 1].Replace(EXPIRATION_SUFFIX, string.Empty);

            RedisValue expiryRedis = results[i];
            long ticks;
            if (long.TryParse(expiryRedis, out ticks))
            {
                DateTime expiry = new DateTime(ticks, DateTimeKind.Utc);
                if (expiry <= DateTime.UtcNow)
                    expiredKeys.Add(key); // expired: add to list for removal
                else
                    ret.Add(key);
            }
            else
                ret.Add(key);
        }

        // remove any expired keys from list
        if (expiredKeys.Count > 0)
        {
            IBatch batch = db.CreateBatch();
            batch.SetRemoveAsync(cacheKey, expiredKeys.ConvertAll(x => (RedisValue)x).ToArray());
            foreach (string expiredKey in expiredKeys)
            {
                batch.KeyDeleteAsync(expiredKey);
            }
            batch.Execute();
        }

        return ret;
   }

    public static void RemoveKeyAndExpiration(IDatabase db, string key, ITransaction transaction)
    {
        // remove the key from the list and its corresponding expiration value
        string expiryKey = $"{key}{EXPIRATION_SUFFIX}";
        transaction.SetRemoveAsync(ALL_KEYS, key);
        transaction.KeyDeleteAsync(expiryKey);
    }

}

注意：StoreKeyAndExpiration 和RemoveKeyAndExpiration 方法都采用ITransaction，因为我在执行这些操作时会同时添加或删除缓存中的项目，所以我想将它们全部打包到一个事务中。事务不会在此处执行，以防调用方法要向其添加更多操作。