#424 √ invalid
Dennis Krupenik

named_scope does not respect eager loading

Reported by Dennis Krupenik | June 15th, 2008 @ 12:42 PM 


class Person
  has_many :messages
end

class Message
  belongs_to :person
  named_scope :unread, :conditions => { :is_read => false }
end

@person = Person.first(:include => :messages) # performs an sql query
@person.messages.unread # performs another sql query. should it?
@person.messages.find_all { |msg| !msg.is_read } # does not perform sql query.
@person.messages.unread.find_all { true } # completely ignores '.unread'. should it?

i'm not sure whether it is a bug or a feature.

is there a way to utilize existing named_scopes to perform filtering on already loaded associations without additional queries?

Comments and changes to this ticket

  • elDub

    elDub July 17th, 2008 @ 03:24 PM

    • → Tag changed from “” to “eager_loading named_scope”

    I have been battling with this issue as well. I think the problem is more related to 'has_one' relationships though. 

    class Document < ActiveRecord::Base
  has_one :revision, :class_name => 'Document', :foreign_key => 'prior_revision_id'
  belongs_to :prior_revision, :class_name => 'Document', :foreign_key => 'prior_revision_id'
  
  named_scope :active, :conditions => { :active => true }
  named_scope :inactive, :conditions => { :active => false }
end

    And then in script/console: 

    Loading development environment (Rails 2.1.0)
>> d1 = Document.create(:active => false, :title => 'd1', :body => 'text')
=> #<Document id: 1, prior_revision_id: nil, title: "d1", body: "text", active: false, created_at: "2008-07-17 14:18:36", updated_at: "2008-07-17 14:18:36">
>> d2 = d1.create_revision(:active => true, :title => 'd2', :body => 'new text')
=> #<Document id: 2, prior_revision_id: 1, title: "d2", body: "new text", active: true, created_at: "2008-07-17 14:19:14", updated_at: "2008-07-17 14:19:14">

>> doc = Document.find(1, :include => :revision)
=> #<Document id: 1, prior_revision_id: nil, title: "d1", body: "text", active: false, created_at: "2008-07-17 14:18:36", updated_at: "2008-07-17 14:18:36">
>> doc.revision
=> #<Document id: 2, prior_revision_id: 1, title: "d2", body: "new text", active: true, created_at: "2008-07-17 14:19:14", updated_at: "2008-07-17 14:19:14">

>> ns_doc = Document.inactive.find(:all, :include => :revision)[0]
=> #<Document id: 1, prior_revision_id: nil, title: "d1", body: "text", active: false, created_at: "2008-07-17 14:18:36", updated_at: "2008-07-17 14:18:36">
>> ns_doc.revision
=> nil

    Note how the attempt to use eager loading within a named scope request causes the same document (id: 1) to NOT be able to access it's revision.

  • elDub

    elDub July 17th, 2008 @ 03:37 PM

    Please forgive/ignore my prior post. After re-thinking it, it is a different issue which I will create a new post for.

  • Tarmo Tänav

    Tarmo Tänav September 18th, 2008 @ 06:51 AM

    • → Tag changed from “eager_loading named_scope” to “eager_loading named_scope”
    • → State changed from “new” to “invalid”

    Since conditions on named_scope's can be arbitrarily complex SQL snippets it is impossible to filter the association by the named scope in AR alone, making an exception for simple hash based conditions does not seem likely to happen.

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