Rails - Oct 2006 - Two-way eager loading?

My problem is that I have two classes where the eager loading isn''t
working as well as I would hope...

Here are my two classes:

class Daynote < ActiveRecord::Base
  belongs_to :userplace

class Userplace < ActiveRecord::Base
    has_many :daynote, :dependent => true

When I show my userplaces, I want to get the associated daynotes with
them, so I am doing:

    @userplace = Userplace.find(params[:id],:include => :daynote)

What I''m seeing is that @userplace.daynote uses the array of objects
from the eager load.  That''s what I want, since it cuts out a lot of
queries.  But then if I pass the daynote object to another function or
partial, and then use daynote.userplace (the inverse), it has to do a
query to look up the userplace, again.  I would think I''ve already
loaded that association, so it would use the cached version, but it
doesn''t.

Now, if I switch the load to:

    @userplace = Userplace.find(params[:id],:include =>
{:daynote=>:userplace))

then it works, but that''s an ugly hack since now it includes the
userplace columns twice in the SQL. OTOH, it saves a lot of query time.

Any ideas?  It''s very possible I''m missing something
fundamental here
but I''m pretty frustrated.

Thanks,
Smackfu


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Smackfu-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org wrote:
> My problem is that I have two classes where the eager loading
isn''t
> working as well as I would hope...
> 
> Here are my two classes:
> 
> class Daynote < ActiveRecord::Base
>   belongs_to :userplace
> 
> class Userplace < ActiveRecord::Base
>     has_many :daynote, :dependent => true
> 
> When I show my userplaces, I want to get the associated daynotes with
> them, so I am doing:
> 
>     @userplace = Userplace.find(params[:id],:include => :daynote)
> 
> What I''m seeing is that @userplace.daynote uses the array of
objects
> from the eager load.  That''s what I want, since it cuts out a lot
of
> queries.  But then if I pass the daynote object to another function or
> partial, and then use daynote.userplace (the inverse), it has to do a
> query to look up the userplace, again.  I would think I''ve already
> loaded that association, so it would use the cached version, but it
> doesn''t.
Yes, at present eager loading does not set the back-link to the
parent object if a reciprocal belongs_to exists in the eagerly-loaded
model.  To implement this the construct_association method in
class JoinDependency would have to be modified to first find such a
reciprocal association, and then set this to the parent object.

Until then, you''ll have to manually fix-up your back pointers, perhaps
in an after_find method:

class Userplace < ActiveRecord::Base
   def after_find
     daynotes.each { |dn| dn.userplace = self } if daynotes.loaded?
   end
end

-- 
We develop, watch us RoR, in numbers too big to ignore.


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