Remove/Delete all/one item from StackExchange.Redis cache

Question

I am using StackExchange.Redis client with Azure Redis Cache Service. Here is my class,

public class RedisCacheService : ICacheService
{
    private readonly ISettings _settings;
    private readonly IDatabase _cache;

    public RedisCacheService(ISettings settings)
    {
        _settings = settings;
        var connectionMultiplexer = ConnectionMultiplexer.Connect(settings.RedisConnection);
        _cache = connectionMultiplexer.GetDatabase();
    }

    public bool Exists(string key)
    {
        return _cache.KeyExists(key);
    }

    public void Save(string key, string value)
    {
        var ts = TimeSpan.FromMinutes(_settings.CacheTimeout);
        _cache.StringSet(key, value, ts);
    }

    public string Get(string key)
    {
        return _cache.StringGet(key);
    }

    public void Remove(string key)
    {
        // How to remove one
    }

    public void Clear()
    {
        // How to remove all
    }
}

Update: From the help of Marc, Here is my final class

public class RedisCacheService : ICacheService
{
    private readonly ISettings _settings;
    private readonly IDatabase _cache;
    private static ConnectionMultiplexer _connectionMultiplexer;

    static RedisCacheService()
    {
        var connection = ConfigurationManager.AppSettings["RedisConnection"];
        _connectionMultiplexer = ConnectionMultiplexer.Connect(connection);
    }

    public RedisCacheService(ISettings settings)
    {
        _settings = settings;
        _cache = _connectionMultiplexer.GetDatabase();
    }

    public bool Exists(string key)
    {
        return _cache.KeyExists(key);
    }

    public void Save(string key, string value)
    {
        var ts = TimeSpan.FromMinutes(_settings.CacheTimeout);
        _cache.StringSet(key, value, ts);
    }

    public string Get(string key)
    {
        return _cache.StringGet(key);
    }

    public void Remove(string key)
    {
        _cache.KeyDelete(key);
    }

    public void Clear()
    {
        var endpoints = _connectionMultiplexer.GetEndPoints(true);
        foreach (var endpoint in endpoints)
        {
            var server = _connectionMultiplexer.GetServer(endpoint);
            server.FlushAllDatabases();    
        }
    }
}

Now I don't know how to remove all items or single item from redis cache.

Answer 1

To remove a single item:

_cache.KeyDelete(key);

To remove all involves the FLUSHDB or FLUSHALL redis command; both are available in StackExchange.Redis; but, for reasons discussed here, they are not on the IDatabase API (because: they affect servers, not logical databases).

As per the "So how do I use them?" on that page:

server.FlushDatabase(); // to wipe a single database, 0 by default
server.FlushAllDatabases(); // to wipe all databases

(quite possibly after using GetEndpoints() on the multiplexer)

Answer 2

I could not able to flush database in Azure Redis Cache, got this error:

This operation is not available unless admin mode is enabled: FLUSHDB

Instead iterate through all keys to delete:

var endpoints = connectionMultiplexer.GetEndPoints();
var server = connectionMultiplexer.GetServer(endpoints.First());
//FlushDatabase didn't work for me: got error admin mode not enabled error
//server.FlushDatabase();
var keys = server.Keys();
foreach (var key in keys)
{
  Console.WriteLine("Removing Key {0} from cache", key.ToString());
  _cache.KeyDelete(key);
}

Answer 3

Both answers by @Rasi and @Marc Gravell contain pieces of code needed. Based on above, here is working snippet assuming there is just 1 server:

You need to connect to redis with allowAdmin=true, one way to obtain such options is to assign AllowAdmin to already parsed string:

var options = ConfigurationOptions.Parse("server:6379");
options.AllowAdmin = true;
var redis = ConnectionMultiplexer.Connect(options);

Then to flush all databases:

var endpoints = redis.GetEndPoints();
var server = redis.GetServer(endpoints[0]);
server.FlushAllDatabases();

Above will work on any redis deployment, not just Azure.

Answer 4

You can delete hash as well ie if you want to clear specific value from any cached list. For example, we have an emp list and inside with different department as cached.

public static void DeleteHash(string key, string cacheSubKey)
        {
            if (string.IsNullOrEmpty(key))
                throw new ArgumentNullException("key");

            Cache.HashDelete(key, cacheSubKey);
        }

so you can pass Key name and cache subkey as well.

Answer 5

To Remove an item from List in Distributed cache use ListRemoveAsync() function supported by Distributed cache library and can be accessed through IDistributedCache interface

 public async Task RemoveListByIndexAsync(string key, string cacheValue)
 {
   RedisValue redisValue = cacheValue // value of item in the list to be removed;
   await _cache.ListRemoveAsync(key, redisValue);
 }

• key - cacahe key redisValue
• item - item in the list to be removed.

Note - Make sure that the Redis value which has to be removed should exactly the item of the list in the existing in the cache.