Let''s say we have two models with a plain has_many/belongs_to
relationship.
class Driver
has_one :car
end
class Car
belongs_to :driver
end
The question is this: Why isn''t the car''s parent driver cached
when
we
eager load it? So the following snippet (as impractical as it is,
it''s
just an example) would just result in one hit (as opposed to
ActiveRecord''s current behavior, which hits the db each time that
#driver is called).
@driver = Driver.find(:first, :include => :car)
@driver.car.driver.car.driver.car.driver.car
Is there a reason for the current behavior?
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---
Pat Nakajima wrote:> Let''s say we have two models with a plain has_many/belongs_to > relationship. > > class Driver > has_one :car > end > class Car > belongs_to :driver > end > > The question is this: Why isn''t the car''s parent driver cached when > we > eager load it? So the following snippet (as impractical as it is, > it''s > just an example) would just result in one hit (as opposed to > ActiveRecord''s current behavior, which hits the db each time that > #driver is called). > > @driver = Driver.find(:first, :include => :car) > @driver.car.driver.car.driver.car.driver.car > > Is there a reason for the current behavior?Yep, you''re correct, this is silly, and a known deficiency in ActiveRecord. Usually, this comes up in situations where you are calling a method on car from a method in driver. The method in Car in turn needs some information about Driver. The quick fix for this is to send a reference to Driver to the method in Car instead of having the car rely on it''s one #driver method: class Driver < ActiveRecord::Base has_one :car def some_driver_method self.car.some_car_method(args,self) end end class Car <ActiveRecord::Base belongs_to :driver def some_car_method(args,dvr=self.driver) dvr.some_attribute end end If this seems like a hack, it is. You might also checkout DataMapper (http://datamapper.org/) which solves this problem, but is not really mature enough, IMHO. (see http://blog.antarestrader.com/?p=33 for My Humble Opinion) -- Posted via http://www.ruby-forum.com/. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
On 7 Feb 2008, at 19:05, Starr Trader wrote:> > Pat Nakajima wrote: >> Let''s say we have two models with a plain has_many/belongs_to >> relationship. >> >> class Driver >> has_one :car >> end >> class Car >> belongs_to :driver >> end >> >> The question is this: Why isn''t the car''s parent driver cached when >> we >> eager load it? So the following snippet (as impractical as it is, >> it''s >> just an example) would just result in one hit (as opposed to >> ActiveRecord''s current behavior, which hits the db each time that >> #driver is called). >> >> @driver = Driver.find(:first, :include => :car) >> @driver.car.driver.car.driver.car.driver.car >> >> Is there a reason for the current behavior? > > Yep, you''re correct, this is silly, and a known deficiency in > ActiveRecord. Usually, this comes up in situations where you are > calling a method on car from a method in driver. The method in Car in > turn needs some information about Driver. The quick fix for this is > to > send a reference to Driver to the method in Car instead of having the > car rely on it''s one #driver method: >You could also manaually set the association target. I suppose that in general it is non trivial to figure out which association (or even associations) is the reverse association (especially with more complication associations using conditions etc...). Fred> class Driver < ActiveRecord::Base > has_one :car > def some_driver_method > self.car.some_car_method(args,self) > end > end > > class Car <ActiveRecord::Base > belongs_to :driver > def some_car_method(args,dvr=self.driver) > dvr.some_attribute > end > end > > If this seems like a hack, it is. You might also checkout DataMapper > (http://datamapper.org/) which solves this problem, but is not really > mature enough, IMHO. (see http://blog.antarestrader.com/?p=33 for My > Humble Opinion) > -- > Posted via http://www.ruby-forum.com/. > > >--~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---