Question

Say I have a system table ‘categories’ with 2 fixed records. The user will not be allowed to delete these 2 but may wish to add their own to extend their list. I need to be able to pull out the ‘garden’ category at certain times, e.g when creating a garden project.

A class attribute reader that returns the garden instance would do the job, but I would like to know how this can be improved with caching?

I believe memoization would only work per process which is almost pointless here. I would like it to be set once (perhaps the first time it’s accessed or on app start-up) and just remain in cache for future use.

Example setup:

class Project < ActiveRecord::Base
  belongs_to :category
end

class Category < SystemTable
  cattr_reader :garden
  def self.garden
    @@garden ||= self.find_by_name('garden')
  end  
end

Answer 1

How about the approach shown below, which will retrieve the garden instance once when the Category class is loaded:

class Category < SystemTable 
  GARDEN = self.find_by_name('garden')
end

Now whenever you need the garden category you can use Category::GARDEN.