DbCharmer custom shard method allow you to shard with mod of integer

mod.rb

# DbCharmer custom sharding method.
# :method => :mod

module DbCharmer
  module Sharding
    module Method
      class Mod 
        attr_accessor :mods
        attr_accessor :all

        def initialize(config)
          @mods = config[:mods] ? config[:mods].clone : raise(ArgumentError, "No :mods defined!")
          @all  = 0 
          config[:mods].keys.each do |m| 
            next if m == :default
            @all += 1
          end 
        end 

        def shard_for_key(key)
          return mods[:default] if key == :default
          key_mod = key.to_i % all 
          if mods["mod_#{key_mod.to_s}".to_sym]
            return mods["mod_#{key_mod.to_s}".to_sym]
          elsif mods[:default]
            return mods[:default]
          else
            raise ArgumentError, "Invalid key value, no shards found for this key!"
          end 
        end 

        def support_default_shard?
          mods.has_key?(:default)
        end 
      end 
    end 
  end 
end

shard_initializer.rb

MOD_SHARDING = { 
  :mod_0   => :shard_one,
  :mod_1   => :shard_two,
  :default => :shard_one
}

DbCharmer::Sharding.register_connection(
  :name   => :sharded_texts,
  :method => :mod,
  :mods   => MOD_SHARDING
)

text.rb

class Text < ActiveRecord::Base
  db_magic :sharded => { 
    :key                => :id,
    :sharded_connection => :sharded_texts
  }
end