Nest

Object Oriented Keys for Redis.

Description

If you are familiar with databases like Redis and libraries like Ohm you already know how important it is to craft the keys that will hold the data.

>> redis = Redic.new
>> redis.call("HSET", "Event:3", "name", "Redis Meetup")
>> redis.call("HGET", "Event:3", "name")
=> ["Redis Meetup"]

It is a design pattern in key-value databases to use the key to simulate structure, and you can read more about this in the case study for a Twitter clone.

Nest helps you generate those keys by providing chainable namespaces that are already connected to Redis:

>> event = Nest.new("Event")
>> event[3].call("HSET", "name", "Redis Meetup")
>> event[3].call("HGET", "name")
=> ["Redis Meetup"]

Alternatively, you can send the Redis commands as messages to Nest, and if the method definition is missing it will forward the command to Redis:

>> event = Nest.new("Event")
>> event[3].hset("name", "Redis Meetup")
>> event[3].hget("name")
=> ["Redis Meetup"]

Usage

To create a new namespace:

>> ns = Nest.new("foo")
=> "foo"

>> ns["bar"]
=> "foo:bar"

>> ns["bar"]["baz"]["qux"]
=> "foo:bar:baz:qux"

And you can use any object as a key, not only strings:

>> ns[:bar][42]
=> "foo:bar:42"

In a more realistic tone, lets assume you are working with Redis and dealing with events:

>> event = Nest.new("Event")
=> "Event"

>> id = event[:id].incr
=> 1

>> event[id].hset("name", "Redis Meetup")
=> 1

>> meetup = event[id]
=> "Event:1"

>> meetup.hget("name")
=> ["Redis Meetup"]

API

call: Receives a Redis command and its arguments, and returns the reply from the Redis server. If the reply from Redis is an error, an instance of RuntimeError is returned.

call!: Similar to call, but instead of returning an instance of RuntimeError when the command fails, the error is raised.

queue: Receives the same kind of arguments as call, but enqueues the command in a transaction.

commit: Commits the transaction and returns the reply from Redis.

Any call to a missing method will result in Nest converting the method name to a Redis command and applying the arguments in an invocation to call.

For example:

ns = Nest.new("foo")
ns.append("hello,")
ns.append(" world")
ns.get

Is equivalent to:

ns = Nest.new("foo")
ns.call("APPEND", "hello,")
ns.call("APPEND", " world")
ns.call("GET")

Supplying your existing Redis instance

You can supply a Redic instance as a second parameter. If you don't, a default instance is created for you:

>> redis = Redic.new("redis://localhost:6379")
=> #<Redic:0x007fa640845f10 ...>

>> event = Nest.new("Event", redis)
=> "Event"

>> event[:id].call("TYPE")
=> "string"

Nest objects respond to redis and return a Redic instance. It is automatically reused when you create a new namespace, and you can reuse it when creating a new instance of Nest:

>> event = Nest.new("Event", meetup.redis)
=> "Event"

Nest allows you to execute all the Redis commands that expect a key as the first parameter. If you use any other command, the result can be unexpected.

Differences with redis-namespace

redis-namespace wraps Redis and translates the keys back and forth transparently.

Use redis-namespace when you want all your application keys to live in a different scope.

Use Nest when you want to use the keys to represent structure.

Tip: instead of using redis-namespace, it is recommended that you run a different instance of redis-server. Translating keys back and forth is not only delicate, but unnecessary and counterproductive.

Differences with Ohm

Ohm lets you map Ruby objects to Redis with little effort. It not only alleviates you from the pain of generating keys for each object, but also helps you when dealing with references between objects.

Use Ohm when you want to use Redis as your database.

Use Nest when mapping objects with Ohm is not possible or overkill.

Tip: Ohm uses Nest internally to deal with keys. Having a good knowledge of Nest will let you extend Ohm to suit your needs.

Installation

$ gem install nest