This is not an ORM. People that are wrapping ORM’s around Redis are missing the point.
The killer feature of Redis is that it allows you to perform atomic operations on individual data structures, like counters, lists, and sets. The atomic part is HUGE. Using an ORM wrapper that retrieves a "record", updates values, then sends those values back, removes the atomicity, cutting the nuts off the major advantage of Redis. Just use MySQL, k?
This gem provides a Rubyish interface to Redis, by mapping Redis data types
to Ruby objects, via a thin layer over the redis gem. It offers several advantages
over the lower-level redis-rb API:
- Easy to integrate directly with existing ORMs - ActiveRecord, DataMapper, etc. Add counters to your model!
- Complex data structures are automatically Marshaled (if you set :marshal => true)
- Integers are returned as integers, rather than '17'
- Higher-level types are provided, such as Locks, that wrap multiple calls
This gem originally arose out of a need for high-concurrency atomic operations; for a fun rant on the topic, see An Atomic Rant, or scroll down to Atomic Counters and Locks in this README.
There are two ways to use Redis::Objects, either as an include in a model class (to
tightly integrate with ORMs or other classes), or standalone by using classes such
as Redis::List and Redis::SortedSet.
Add it to your Gemfile as:
gem 'redis-objects'Redis::Objects needs a handle created by Redis.new or a ConnectionPool:
The recommended approach is to use a ConnectionPool since this guarantees that most timeouts in the redis client
do not pollute your existing connection. However, you need to make sure that both :timeout and :size are set appropriately
in a multithreaded environment.
require 'connection_pool'
Redis::Objects.redis = ConnectionPool.new(size: 5, timeout: 5) { Redis.new(:host => '127.0.0.1', :port => 6379) }Redis::Objects can also default to Redis.current if Redis::Objects.redis is not set.
Redis.current = Redis.new(:host => '127.0.0.1', :port => 6379)(If you're on Rails, config/initializers/redis.rb is a good place for this.)
Remember you can use Redis::Objects in any Ruby code. There are no dependencies
on Rails. Standalone, Sinatra, Resque - no problem.
Alternatively, you can set the redis handle directly:
Redis::Objects.redis = Redis.new(...)Finally, you can even set different handles for different classes:
class User
include Redis::Objects
end
class Post
include Redis::Objects
end
# you can also use a ConnectionPool here as well
User.redis = Redis.new(:host => '1.2.3.4')
Post.redis = Redis.new(:host => '5.6.7.8')As of 0.7.0, redis-objects now autoloads the appropriate Redis::Whatever
classes on demand. Previous strategies of individually requiring redis/list
or redis/set are no longer required.
Including Redis::Objects in a model class makes it trivial to integrate Redis types
with an existing ActiveRecord, DataMapper, Mongoid, or similar class. Redis::Objects
will work with any class that provides an id method that returns a unique value.
Redis::Objects automatically creates keys that are unique to each object, in the format:
model_name:id:field_name
For illustration purposes, consider this stub class:
class User
include Redis::Objects
counter :my_posts
def id
1
end
end
user = User.new
user.id # 1
user.my_posts.increment
user.my_posts.increment
user.my_posts.increment
puts user.my_posts.value # 3
user.my_posts.reset
puts user.my_posts.value # 0
user.my_posts.reset 5
puts user.my_posts.value # 5Here's an example that integrates several data types with an ActiveRecord model:
class Team < ActiveRecord::Base
include Redis::Objects
lock :trade_players, :expiration => 15 # sec
value :at_bat
counter :hits
counter :runs
counter :outs
counter :inning, :start => 1
list :on_base
list :coaches, :marshal => true
set :outfielders
hash_key :pitchers_faced # "hash" is taken by Ruby
sorted_set :rank, :global => true
endFamiliar Ruby array operations Just Work (TM):
@team = Team.find_by_name('New York Yankees')
@team.on_base << 'player1'
@team.on_base << 'player2'
@team.on_base << 'player3'
@team.on_base # ['player1', 'player2', 'player3']
@team.on_base.pop
@team.on_base.shift
@team.on_base.length # 1
@team.on_base.delete('player2')Sets work too:
@team.outfielders << 'outfielder1'
@team.outfielders << 'outfielder2'
@team.outfielders << 'outfielder1' # dup ignored
@team.outfielders # ['outfielder1', 'outfielder2']
@team.outfielders.each do |player|
puts player
end
player = @team.outfielders.detect{|of| of == 'outfielder2'}And you can do unions and intersections between objects (kinda cool):
@team1.outfielders | @team2.outfielders # outfielders on both teams
@team1.outfielders & @team2.outfielders # in baseball, should be empty :-)Counters can be atomically incremented/decremented (but not assigned):
@team.hits.increment # or incr
@team.hits.decrement # or decr
@team.hits.incr(3) # add 3
@team.runs = 4 # exceptionDefining a different method as the id field is easy
class User
include Redis::Objects
redis_id_field :uid
counter :my_posts
end
user.uid # 195137a1bdea4473
user.my_posts.increment # 1Finally, for free, you get a redis method that points directly to a Redis connection:
Team.redis.get('somekey')
@team = Team.new
@team.redis.get('somekey')
@team.redis.smembers('someset')You can use the redis handle to directly call any Redis API command.
There is a Ruby class that maps to each Redis type, with methods for each
Redis API command.
Note that calling new does not imply it's actually a "new" value - it just
creates a mapping between that Ruby object and the corresponding Redis data
structure, which may already exist on the redis-server.
The counter_name is the key stored in Redis.
@counter = Redis::Counter.new('counter_name')
@counter.increment # or incr
@counter.decrement # or decr
@counter.increment(3)
puts @counter.valueThis gem provides a clean way to do atomic blocks as well:
@counter.increment do |val|
raise "Full" if val > MAX_VAL # rewind counter
endSee the section on Atomic Counters and Locks for cool uses of atomic counter blocks.
A convenience class that wraps the pattern of using setnx to perform locking.
@lock = Redis::Lock.new('serialize_stuff', :expiration => 15, :timeout => 0.1)
@lock.lock do
# do work
endThis can be especially useful if you're running batch jobs spread across multiple hosts.
Simple values are easy as well:
@value = Redis::Value.new('value_name')
@value.value = 'a'
@value.deleteComplex data is no problem with :marshal => true:
@account = Account.create!(params[:account])
@newest = Redis::Value.new('newest_account', :marshal => true)
@newest.value = @account.attributes
puts @newest.value['username']Lists work just like Ruby arrays:
@list = Redis::List.new('list_name')
@list << 'a'
@list << 'b'
@list.include? 'c' # false
@list.values # ['a','b']
@list << 'c'
@list.delete('c')
@list[0]
@list[0,1]
@list[0..1]
@list.shift
@list.pop
@list.clear
# etcYou can bound the size of the list to only hold N elements like so:
# Only holds 10 elements, throws out old ones when you reach :maxlength.
@list = Redis::List.new('list_name', :maxlength => 10)Complex data types are serialized with :marshal => true:
@list = Redis::List.new('list_name', :marshal => true)
@list << {:name => "Nate", :city => "San Diego"}
@list << {:name => "Peter", :city => "Oceanside"}
@list.each do |el|
puts "#{el[:name]} lives in #{el[:city]}"
endNote: If you run into issues, with Marshal errors, refer to the fix in Issue #176.
Hashes work like a Ruby Hash, with a few Redis-specific additions. (The class name is "HashKey" not just "Hash", due to conflicts with the Ruby core Hash class in other gems.)
@hash = Redis::HashKey.new('hash_name')
@hash['a'] = 1
@hash['b'] = 2
@hash.each do |k,v|
puts "#{k} = #{v}"
end
@hash['c'] = 3
puts @hash.all # {"a"=>"1","b"=>"2","c"=>"3"}
@hash.clearRedis also adds incrementing and bulk operations:
@hash.incr('c', 6) # 9
@hash.bulk_set('d' => 5, 'e' => 6)
@hash.bulk_get('d','e') # "5", "6"Remember that numbers become strings in Redis. Unlike with other Redis data types,
redis-objects can't guess at your data type in this situation, since you may
actually mean to store "1.5".
Sets work like the Ruby Set class. They are unordered, but guarantee uniqueness of members.
@set = Redis::Set.new('set_name')
@set << 'a'
@set << 'b'
@set << 'a' # dup ignored
@set.member? 'c' # false
@set.members # ['a','b']
@set.members.reverse # ['b','a']
@set.each do |member|
puts member
end
@set.clear
# etcYou can perform Redis intersections/unions/diffs easily:
@set1 = Redis::Set.new('set1')
@set2 = Redis::Set.new('set2')
@set3 = Redis::Set.new('set3')
members = @set1 & @set2 # intersection
members = @set1 | @set2 # union
members = @set1 + @set2 # union
members = @set1 ^ @set2 # difference
members = @set1 - @set2 # difference
members = @set1.intersection(@set2, @set3) # multiple
members = @set1.union(@set2, @set3) # multiple
members = @set1.difference(@set2, @set3) # multipleOr store them in Redis:
@set1.interstore('intername', @set2, @set3)
members = @set1.redis.get('intername')
@set1.unionstore('unionname', @set2, @set3)
members = @set1.redis.get('unionname')
@set1.diffstore('diffname', @set2, @set3)
members = @set1.redis.get('diffname')And use complex data types too, with :marshal => true:
@set1 = Redis::Set.new('set1', :marshal => true)
@set2 = Redis::Set.new('set2', :marshal => true)
@set1 << {:name => "Nate", :city => "San Diego"}
@set1 << {:name => "Peter", :city => "Oceanside"}
@set2 << {:name => "Nate", :city => "San Diego"}
@set2 << {:name => "Jeff", :city => "Del Mar"}
@set1 & @set2 # Nate
@set1 - @set2 # Peter
@set1 | @set2 # all 3 peopleDue to their unique properties, Sorted Sets work like a hybrid between a Hash and an Array. You assign like a Hash, but retrieve like an Array:
@sorted_set = Redis::SortedSet.new('number_of_posts')
@sorted_set['Nate'] = 15
@sorted_set['Peter'] = 75
@sorted_set['Jeff'] = 24
# Array access to get sorted order
@sorted_set[0..2] # => ["Nate", "Jeff", "Peter"]
@sorted_set[0,2] # => ["Nate", "Jeff"]
@sorted_set['Peter'] # => 75
@sorted_set['Jeff'] # => 24
@sorted_set.score('Jeff') # same thing (24)
@sorted_set.rank('Peter') # => 2
@sorted_set.rank('Jeff') # => 1
@sorted_set.first # => "Nate"
@sorted_set.last # => "Peter"
@sorted_set.revrange(0,2) # => ["Peter", "Jeff", "Nate"]
@sorted_set['Newbie'] = 1
@sorted_set.members # => ["Newbie", "Nate", "Jeff", "Peter"]
@sorted_set.members.reverse # => ["Peter", "Jeff", "Nate", "Newbie"]
@sorted_set.rangebyscore(10, 100, :limit => 2) # => ["Nate", "Jeff"]
@sorted_set.members(:with_scores => true) # => [["Newbie", 1], ["Nate", 16], ["Jeff", 28], ["Peter", 76]]
# atomic increment
@sorted_set.increment('Nate')
@sorted_set.incr('Peter') # shorthand
@sorted_set.incr('Jeff', 4)The other Redis Sorted Set commands are supported as well; see Sorted Sets API.
You are probably not handling atomicity correctly in your app. For a fun rant on the topic, see An Atomic Rant.
Atomic counters are a good way to handle concurrency:
@team = Team.find(1)
if @team.drafted_players.increment <= @team.max_players
# do stuff
@team.team_players.create!(:player_id => 221)
@team.active_players.increment
else
# reset counter state
@team.drafted_players.decrement
endAn atomic block gives you a cleaner way to do the above. Exceptions or returning nil will rewind the counter back to its previous state:
@team.drafted_players.increment do |val|
raise Team::TeamFullError if val > @team.max_players # rewind
@team.team_players.create!(:player_id => 221)
@team.active_players.increment
endHere's a similar approach, using an if block (failure rewinds counter):
@team.drafted_players.increment do |val|
if val <= @team.max_players
@team.team_players.create!(:player_id => 221)
@team.active_players.increment
end
endClass methods work too, using the familiar ActiveRecord counter syntax:
Team.increment_counter :drafted_players, team_id
Team.decrement_counter :drafted_players, team_id, 2
Team.increment_counter :total_online_players # no ID on global counterClass-level atomic blocks can also be used. This may save a DB fetch, if you have a record ID and don't need any other attributes from the DB table:
Team.increment_counter(:drafted_players, team_id) do |val|
TeamPitcher.create!(:team_id => team_id, :pitcher_id => 181)
Team.increment_counter(:active_players, team_id)
endLocks work similarly. On completion or exception the lock is released:
class Team < ActiveRecord::Base
lock :reorder # declare a lock
end
@team.reorder_lock.lock do
@team.reorder_all_players
endClass-level lock (same concept)
Team.obtain_lock(:reorder, team_id) do
Team.reorder_all_players(team_id)
endLock expiration. Sometimes you want to make sure your locks are cleaned up should the unthinkable happen (server failure). You can set lock expirations to handle this. Expired locks are released by the next process to attempt lock. Just make sure you expiration value is sufficiently large compared to your expected lock time.
class Team < ActiveRecord::Base
lock :reorder, :expiration => 15.minutes
endKeep in mind that true locks serialize your entire application at that point. As such, atomic counters are strongly preferred.
Use :expiration and :expireat options to set default expiration.
value :value_with_expiration, :expiration => 1.hour
value :value_with_expireat, :expireat => Time.now + 1.hourCopyright (c) 2009-2013 Nate Wiger. All Rights Reserved. Released under the Artistic License.