Stal

Set algebra solver for Redis

Description

Stal receives an array with an s-expression composed of commands and key names and resolves the set operations in Redis.

Community

Meet us on IRC: #lesscode on freenode.net.

Getting started

Install Redis. On most platforms it's as easy as grabbing the sources, running make and then putting the redis-server binary in the PATH.

Once you have it installed, you can execute redis-server and it will run on localhost:6379 by default. Check the redis.conf file that comes with the sources if you want to change some settings.

Usage

Stal requires a Resp compatible client. To make things easier, resp is listed as a runtime dependency so the examples in this document will work.

require "stal"

# Connect the client to the default host
resp = Resp.new("redis://localhost:6379")

# Use the Redis client to populate some sets
resp.call("SADD", "foo", "a", "b", "c")
resp.call("SADD", "bar", "b", "c", "d")
resp.call("SADD", "baz", "c", "d", "e")
resp.call("SADD", "qux", "x", "y", "z")

Now we can perform some set operations with Stal:

expr = ["SUNION", "qux", ["SDIFF", ["SINTER", "foo", "bar"], "baz"]]

Stal.solve(resp, expr)
#=> ["b", "x", "y", "z"]

Stal translates the internal calls to "SUNION", "SDIFF" and "SINTER" into SDIFFSTORE, SINTERSTORE and SUNIONSTORE to perform the underlying operations, and it takes care of generating and deleting any temporary keys.

Note that the only valid names for the internal commands are "SUNION", "SDIFF" and "SINTER". Any other internal command will raise an error. The outmost command can be any set operation, for example:

expr = ["SCARD", ["SINTER", "foo", "bar"]]

Stal.solve(resp, expr)
#=> 2

If you want to preview the commands Stal will send to generate the results, you can use Stal.explain:

Stal.explain(["SINTER", ["SUNION", "foo", "bar"], "baz"])
#  [["SUNIONSTORE", "stal:0", "foo", "bar"],
#   ["SINTER", "stal:0", "baz"]]

All commands are pipelined and wrapped in a MULTI/EXEC transaction.

Installation

Add this to your application's shard.yml:

dependencies:
  stal:
    github: soveran/stal-crystal
    branch: master