Rails 3 ActiveRecord::Relation random associations behavior - associations

Question

I am currently having a strange issue with an application migrated from rails 2.3.8 to rails 3 (3.0.1, 3.0.2, 3.0.3).
At random moments associations behave strangely. In some cases, an associated object will return the Relation object, instead of the corresponding model. This seems to happen mostly on polymorphic associations. For example:
class A
belongs_to :b, :polymorphic => true
end
class B
has_many :a, :as => :source
end
When invoking "a.b" this will "sometimes" return the Relation object (causing a "undefined method ... for ActiveRecord::Relation" error to raise) and some other times it will return the correct B object.
When the relation object is returned, it may sometimes be "fixed" temporarily by restarting the server, but it will eventually show up again.
Another issue i get is that when "getting" associated objects, sometimes the required filters are not automatically applied (where element id = ...). this causes the query to return the first object in the table and not the correct associated object.
This is becoming a very frustrating issue, specially since i don't seem to find anyone else with this or similar issues.
All finder methods in the application have been migrated to the new rails form, but this strange behavior remains.
The current configuration being used is:
Ubuntu 10
nginx server
passenger (3.0.2)
rails (3.0.3)
ruby 1.9.2p0 (2010-08-18 revision 29036)

Answer 1

After digging a bit deeper into the Active Record code, my co-worker and I found that the belongs_to_association.rb and belongs_to_polymorphic_association.rb were still using the old finder methods in the "find_target" method.
We ran a couple tests by logging the resulting objects of this method from different queries and discovered the old finders were returning the ActiveRecord::Relation at random moments (loading the same object it would sometimes return the object and other times the Relation object).
We overrode the find_target method for these 2 classes in initializer files, changing the finders used there to the new rails3 format (klass.select(...).where(...), etc). This seems to have solved the issue.
The "has_many" association files are already using the new format, so these haven't caused any issues.
We applied these "fixes" to the rails 3.0.3 and hope that they will be resolved in future releases.
Here are our initializer files in case someone else bumps into this problem:
belongs_to_polymorphic_association.rb:
#initializers/belongs_to_polymorphic_association.rb
module ActiveRecord
# = Active Record Belongs To Polymorphic Association
module Associations
class BelongsToPolymorphicAssociation < AssociationProxy #:nodoc:
private
def find_target
return nil if association_class.nil?
target =
if #reflection.options[:conditions]
association_class.select(#reflection.options[:select]).where(conditions).where(:id => #owner[#reflection.primary_key_name]).includes(#reflection.options[:include]).first
else
association_class.select(#reflection.options[:select]).where(:id => #owner[#reflection.primary_key_name]).includes(#reflection.options[:include]).first
end
set_inverse_instance(target, #owner)
target
end
end
end
end
belongs_to_association.rb:
#initializers/belongs_to_association.rb
module ActiveRecord
# = Active Record Belongs To Associations
module Associations
class BelongsToAssociation < AssociationProxy #:nodoc:
private
def find_target
key_column = (#reflection.options[:primary_key]) ? #reflection.options[:primary_key].to_sym : :id
options = #reflection.options.dup
(options.keys - [:select, :include, :readonly]).each do |key|
options.delete key
end
options[:conditions] = conditions
the_target= #reflection.klass.select(options[:select]).where(key_column => #owner[#reflection.primary_key_name]).where(options[:conditions]).includes(options[:include]).readonly(options[:readonly]).order(options[:order]).first if #owner[#reflection.primary_key_name]
set_inverse_instance(the_target, #owner)
the_target
end
end
end
end
Hope this is useful for someome

Answer 2

Thanks for sharing this. The problem with associations gone. But I still had this issue even with straight "find" method.
#post = Post.find(params[:id)
#post.update_attributes...
will fail with ActiveRecord::Relation error. However
#post = Post.find_by_id(params[:id])
#post.update_attributes...
will work
Seems like strange lazy loading behaviour