Rails Ruby on Rails → 2.x

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  cainlevy July 9th, 2008 @ 12:09 AM

  After some discussion in #rails-contrib, I came to see this new option as completing a triad:

  • :include names associations that should be eager loaded but may also be needed for sql references (e.g. in conditions, orders, etc.)
  • :joins names associations that are needed for sql references but should not be loaded
  • :load names associations that should be loaded but are not needed for sql references

  API bloat is something to be taken seriously. In this case I feel like the new option rounds out the use cases, and is not bloat.

  Thoughts?

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  hiroshi August 17th, 2008 @ 01:36 PM

  I express approval about the :load option.

  cainlevy suggested capabilities against optimization, moreover, I point out that a problem of 'join' eager loading has_many association with group option.

  For example, Ticket has_many :tags, and I would like to find tickets which has tags, 'foo' and 'bar', also I prefer eager loading because search result will show tags for each ticket. The code can be like that:

  
  #
  Ticket.find(:all,
    :include => :tags,
    :joins => "INNER JOIN tags AS t ON t.ticket_id = tickets.id",
    :conditions => ["t.name IN (:tags)", {:tags => ['foo', 'bar']}],
    :group => "t.ticket_id HAVING COUNT(t.ticket_id) >= 2")
  

  This call of find() internally uses find_with_associations (join eager loading) instead of preload_associations. Any of the resulted ticket included only one tag (because ticket is grouped by own id), but they may have two or more tags.

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  hiroshi August 17th, 2008 @ 01:49 PM

  I also found a quick option (a hack?) for explicit association preloading.

  
  tickets = Ticket.find(:all,
  # :include => :tags,
    :joins => "INNER JOIN tags AS t ON t.ticket_id = tickets.id",
    :conditions => ["t.name IN (:tags)", {:tags => ['foo', 'bar']}],
    :group => "t.ticket_id HAVING COUNT(t.ticket_id) >= 2")
  Ticket.send(:preload_associations, tickets, :tags)
  

  It worked (for me).

• 

  Pratik August 18th, 2008 @ 04:30 PM

  Please discuss in the core mailing list. Meanwhile, you could write a simple plugin with hiroshi's suggestion.

• 

  Pratik August 18th, 2008 @ 04:31 PM

  • State changed from “new” to “wontfix”

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  cainlevy August 18th, 2008 @ 10:38 PM

  I use the following patch in my own project:

  
  class ActiveRecord::Base
    class << self
      private
      def find_every_with_explicit_preloading(options)
        returning find_every_without_explicit_preloading(options) do |records|
          to_load = merge_includes(scope(:find, :load), options[:load])
          preload_associations(records, to_load) if to_load
        end
      end
      alias_method_chain :find_every, :explicit_preloading
  
      VALID_FIND_OPTIONS << :load
    end
  end