Lazy-load model class variable hash

rubyonrails-talk
1

Hi,

I have a number of models which contain almost static data. I don't
want to hit to db when accessing a row, nor do I want to hit memcached.

I am hoping to use a lazy-loaded model class variable hash. This will ensure that the db is hit only once for the life of a mongrel process.

Are there any drawbacks to this solution? Can the code be simplified?

well it's very minor, but you can write @@hash_by_name = Status.find(:all).index_by(&:name)

I've used a similar pattern quite a lot and as far as I can tell it
works fine. If you are going to be using it in a lot of methods, then
you can wrap it up a little, i've got something like

module Caches    module ClassMethod      def caches(name, &block)        define_method(name) do          ivar_name = "cache_#{name}_value"          unless value = instance_variable_get ivar_name            value = instance_eval(&block)            instance_variable_set ivar_name, value          end          value        end      end    end    def self.included(base)      base.extend ClassMethods    end end (written off the top of my head in mail, expect typos).

You can then do something like

class Status ...    class << self      include Caches      caches('all') {Status.find(:all).index_by(&:name)}      caches('something_else') { ...code to compute something else...}    end end

Fred

2

Thanks Frederick, with your help I've reduced the code to:

class Status < ActiveRecord::Base   def self.hash_by_name     @@hash_by_name ||= self.find(:all).index_by(&:name)   end end

I'll use the helper method if I use this a lot in the future.

Thanks!