Servicestack.Redis how to use GetRange feature

Question

I need to use the redis command GETRANGE. I use it this retrieve the hash I store along with the string content, to evaluate if this latter has been changed while using side in memory cache.

Using (RedisClient.cs) I am unable to access get range function as it is not available

How can GETRANGE command be used when working with RedisClient?

Answer 1

The UTF-8 string APIs for GetRange() and SetRange() have now been added to IRedisClient:

public interface IRedisClient
{
    string Slice(string key, int fromIndex, int toIndex);
    long InsertAt(string key, int offset, string value);
    //...
}

and Async versions to:

public interface IRedisClientAsync
{
    ValueTask<string> SliceAsync(string key, int fromIndex, int toIndex, CancellationToken token = default);
    ValueTask<long> InsertAtAsync(string key, int offset, string value, CancellationToken token = default);
    //...
}

This change is available from v6.0.3 that's now available on MyGet.

Answer 2

Update: From version 6.0.3 (ServiceStack.Redis) the feature will be directly accessible from RedisClient. Thanks to mythz for the info.

Exploring GitHub source code you can see that RedisClient extends RedisClientNative, this latter do have the GetRange method available, so the first solution is as follow:

var nativeClient = redisClient as RedisNativeClient;
var prefix = nativeClient?.GetRange(key, from, to)?.FromUtf8Bytes();

This solution is nice and simple and possibly will always work, but we are relying on ServiceStack to always implement RedisClient extending RedisNativeClient, but we can't be 100% sure about it.

The alternative solution is to leverage the LUA script execution feature, where you can:

var prefix = redisClient.ExecLuaAsString("return redis.call('GETRANGE', ARGV[1], ARGV[2], ARGV[3])", key, from, to);

Performance wise the Native approach is slightly faster and uses less memory.