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has_one through doesn't work when going through a collection association

#2912

When using alias_method to override a setter method for a has_one :through association, an undefined method error occurs when the alias method is called:

undefined method update_attributes' for #&lt;Class:0x3e4f298&gt;</code>
</pre>



This bug was introduced between Rails v2.2.1 and v2.2.2 in commit [a5609cd3cf3921cbd17b6314498318da7d522395] in the file has_one_through_association.rb.



This code sets the stage:


class Foo < ActiveRecord::Base
  has_many :foobars
  has_one :bar, :through => :foobars







  alias_method :orig_bar=, :bar=
  def bar=(value)











Now just run this in your console to replicate the problem:


Foo.new.bar = Bar.new



self.orig_bar = value





  end
end



class Foobar < ActiveRecord::Base
  belongs_to :foo
  belongs_to :bar
end



class Bar < ActiveRecord::Base
end

Reported by Thomas Watson · July 15th, 2009 @ 10:43 PM

State: resolved
Milestone: 3.x
Assigned to: Aaron Patterson Aaron Patterson
Importance: none

Activity

  1. Jeremy Kemper
    Jeremy Kemper
    • Milestone changed from 2.x to 3.x

    May 4th, 2010 @ 06:48 PM

  2. Dan Pickett
    Dan Pickett
    • Tag changed from 2.2.2, activerecord, alias_method, associations, has_one_through, update_attributes to 2.2.2, activerecord, alias_method, associations, bugmash, has_one_through, update_attributes

    can a bugmasher review this against master?

    May 9th, 2010 @ 07:20 PM

  3. Lake
    Lake
    • Tag changed from 2.2.2, activerecord, alias_method, associations, bugmash, has_one_through, update_attributes to 2.2.2, 3.0.0.beta, activerecord, alias_method, associations, bugmash, has_one_through, update_attributes

    It appears that this happens even if we don't use alias_method...

    I have posted some code on github to try and help identify the issue. Check the readme for a quick overview.

    http://github.com/ldenman/rails-bm-ticket-2912

    May 14th, 2010 @ 10:49 PM

  4. Jeff Kreeftmeijer
    Jeff Kreeftmeijer
    • Tag changed from 2.2.2, 3.0.0.beta, activerecord, alias_method, associations, bugmash, has_one_through, update_attributes to 2.2.2, 3.0.0.beta, activerecord, alias_method, associations, bugmash, has_one_through, update_attributes, verified

    Verified with Thomas' code snippet against master and Lake's github repo (also, master).

    And here's a cleaned up version of Thomas' code:

    class Foo < ActiveRecord::Base
  has_many :foobars
  has_one :bar, :through => :foobars

  alias_method :orig_bar=, :bar=
  
  def bar=(value)
    self.orig_bar = value
  end
end

class Foobar < ActiveRecord::Base
  belongs_to :foo
  belongs_to :bar
end

class Bar < ActiveRecord::Base
end

    And run this in the console:

    Foo.new.bar = Bar.new

    May 15th, 2010 @ 04:56 PM

  5. Jon Leighton
    Jon Leighton
    • Assigned user set to Aaron Patterson
    • Title changed from has_one through fails when setter is overridden using alias_method to has_one through doesn't work when going through a collection association
    • Tag changed from 2.2.2, 3.0.0.beta, activerecord, alias_method, associations, bugmash, has_one_through, update_attributes, verified to 2.2.2, 3.0.0.beta, activerecord, alias_method, associations, bugmash, has_one_through, patch, update_attributes

    This is not actually a problem with aliases at all.

    The problem is with putting a has_one association :through a collection (i.e. has_many). HasOneThroughAssociation#create_through_record looks up the through association, and expects it to be a single record. On this assumption it uses update_attributes, which obviously isn't defined on a collection. Hence the problem.

    My preferred solution is to make it invalid to put a has_one through a collection. If the user really wants to go through an association that could have many different records, they can explicitly add a has_one in place of the has_many, and use a combination of :order, :conditions etc to be specific about which record they want.

    I've attached a tested patch which prohibits has_one associations going through collections.

    December 19th, 2010 @ 02:19 PM

  6. blatyo
    blatyo

    +1 @ Jon

    December 19th, 2010 @ 02:39 PM

  7. Jon Leighton
    Jon Leighton
    • State changed from new to resolved

    December 23rd, 2010 @ 11:53 PM