A simple key/value store model for Rails using the database and memcache

README.md

Rails Setting model

This is a semi-quick key/value store I put together for a quick way to store temporary data related to what's in my database, in a reliable way. For example, I'm using it to keep track of where a hourly and a daily crontask that processes statistics left off, so it can resume only processing and summarizing new data on the next run.

Code quality most likely is not great, but it works. And I will update this gist as I update my project.

How It Works

The settings table has two columns, a key and a value column. The value column is serialized, so you can technically store almost anything in there. Memcache is also used as a caching layer to minimize database calls.

Example usage

# fetching a value
>> Setting.hello
=> nil

# setting a value, writes it to memcache, and saves or updates a database
# record is the form of {:key => "hello", :value => serialize(["world"])}
>> Setting.hello = ["world"]
=> ["hello"]

# fetching the value again, which will only read from memcache
>> Setting.hello
=> ["hello"]

# force fetch from database and update memcache
>> Setting.hello!
=> ["hello"]

# remove the hello key from memcache and the database
>> Setting.hello = nil
=> nil

# default memcache expire_in option is 6.hours, you can change it...
>> Setting.__cache_expires_in = 1.hour
=> 3600 seconds

create_settings.rb

class CreateSettings < ActiveRecord::Migration
  def self.up
    create_table :settings, :options => "ENGINE=InnoDB DEFAULT CHARSET=utf8" do |t|
      t.string :key
      t.text :value
    end
    
    add_index :settings, :key, :unique => true
  end

  def self.down
    drop_table :settings
  end
end

setting.rb

class Setting < ActiveRecord::Base
  
  serialize :value
  
  class << self
    attr_accessor :__cache
    attr_accessor :__cache_expires_in
  end
  
  def self.method_missing(method, *args)
    
    # init memcache if needed
    @__cache = ActiveSupport::Cache::MemCacheStore.new if @__cache.nil?
    @__cache_expires_in = 6.hours if @__cache_expires_in.nil?
    
    method = method.to_s
    
    # set mode
    if method[-1,1] == "="
      
      if args.size > 0
        # key/value setup
        method = method.chop
        method = method.chop if method[-1,1] == "!"
        value = {:value => args[0]}
        @__cache.write(method, value, :expires_in => @__cache_expires_in)
        setting = self.find(:first, :conditions => {:key => method})
        if value[:value].nil?
          setting.destroy if setting
          @__cache.write(method, nil, :expires_in => 0.seconds)
        else
          setting = self.new if !setting
          setting.key = method.to_s if setting.key.blank?
          setting.value = value
          if setting.save
            return value[:value]
          end
        end
      end
      
    # get mode
    else
      
      # skip memcache?
      if method[-1,1] == "!"
        method = method.chop
        skip_cache = true
      end
      
      if skip_cache.nil? && (result = @__cache.read(method.to_s))
        return result[:value]
      else
        result = self.find(:first, :conditions => {:key => method})
        if result
          @__cache.write(method, result.value, :expires_in => @__cache_expires_in)
          return result.value[:value]
        end
      end
      
    end
    return nil
    
  end
  
end

Very nice, thank you for sharing.

Awesome, thank you.

My version (a little cleaner and without the cache):
` def self.method_missing(method, *args)

method = method.to_s

# set mode
if method[-1, 1] == "=" && args.size > 0

  method    = method.chop
  value     = args[0]
  system_parameter = self.find_by key: method

  if value.empty?
    return system_parameter.destroy if system_parameter
  else
    system_parameter       = self.new unless system_parameter
    system_parameter.key   = method.to_s if system_parameter.key.blank?
    system_parameter.value = value

    return self if system_parameter.save
  end

  # get mode
else
  result = self.find_by key: method
  if result
    return result.value
  end
end

nil

end`