Implement transparent key prefixing

[dguo]

Hi, I noticed that you have this feature on the roadmap, and I'd like to help implement it. Do you have any ideas about how it will work?

[luin]

That will be great. We can give user an option to specify a key prefix:

var redis = new Redis({ keyPrefix: 'app1:' });

and then the keys of every command sent by this instance should get a prefix of 'app1:'. For instance:

1. redis.set('foo', 'bar') will actually send SET app1:foo bar;
2. redis.blpop('key1', 'key2', 'key3', 0) will actually send BLPOP app1:key1 app1:key2 app1:key3 0;

[luin]

We already have a method Command#getKeys for getting keys in a command(https://github.com/luin/ioredis/blob/master/lib/command.js#L85).

[dguo]

Sounds good. What's your opinion on giving the user flexibility for commands that have multiple keys? So something like:

var redis = new Redis({keyPrefix: ['app1:', 'app2:', 'app3:']});
redis.blpop('key1', 'key2', 'key3', 0);  // BLPOP app1:key1 app2:key2 app3:key3 0

Or maybe even allow the user to dynamically set the prefix?

var redis = new Redis({keyPrefix: 'foo:'});
redis.blpop({keyPrefix: ['app1:', 'app2:', 'app3:']}, 'key1', 'key2', 'key3', 0);

I'm not sure how useful this would be.

[luin]

I prefer to keeping this option simple. My intention to add keyPrefix option is to allow multiple apps using one Redis server.keyPrefix is used as a namespace, so a single string is enough.

[dguo]

Ok, that's reasonable. I'll start working on it.

[Delagen]

scanstream match option does not use this prefix

[luin]

@Delagen This has already been discussed. Refer to #239 for more information.