Jun 25, 2009

A better Rails.cache.increment

I started working with Rails.cache.increment and Rails.cache.decrement today but quickly found that it didn’t work as I planned. For example, it seemed that when calling these methods they would return the previous value rather than the newly incremented value. Additionally, if you decided to read directly using Rails.cache.read and the same key, it would always return nil despite being able to call Rails.cache.increment again. Another annoying thing is that if you tried to increment a value that wasn’t in memcached, instead of defaulting to 1, it returned nil. Just all sorts of wacky stuff going on. I decided to just write my own.

# app/models/util/cache.rb

class Util::Cache
  def self.increment(key, amount = 1)
    if (value = Rails.cache.read(key)).nil?
      Rails.cache.write(key, (value = amount))
    else
      Rails.cache.write(key, (value = value + amount))
    end

    return value
  end

  def self.decrement(key, amount = 1)
    if (value = Rails.cache.read(key)).nil?
      value = 0
    else
      Rails.cache.write(key, (value = value - amount))
    end

    return value
  end
end