Forum: Ruby on Rails activerecord :include

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hiddenhippo (Guest)
on 2008-10-17 14:27
(Received via mailing list)
basically I've got a design which has a model describing, say a
folder, and within each folder I associate some notes.  I've built my
models so that a folder can have many notes, and that a note belongs
to a folder.  Now, a folder can belongs to a person, and a person
therefore has many folders.  what I'm attempting to do is display all
the folders for a given user, which is pretty simple as I can simply
so

folders = Person.find(1,:include=>[:folders])

however, what I also want to do is display the most recent note
against each folder.  Although I can do this by simply adding the
notes into my include,

folders = Person.find(1,:include=>[:folders=>:notes])

 I'd really perfer not to load each and every note assigned to each
and every folder.  I've been playing about for a while now trying to
get active record to load my assoicates but only include the first
note for each folder.  can anybody help?  maybe it's not even
possible?  Perhaps I need to change my approach?  Any help/advice
would be greatly appreciated/welcome.

thanks
Frederick C. (Guest)
on 2008-10-17 14:42
(Received via mailing list)
On 17 Oct 2008, at 11:27, hiddenhippo wrote:
> get active record to load my assoicates but only include the first
> note for each folder.  can anybody help?  maybe it's not even
> possible?  Perhaps I need to change my approach?  Any help/advice
> would be greatly appreciated/welcome.
>
:include can't do that - it's fundamentally hard from it's point of
view to only fetch the first record of some collection

Fred
Mark J. (Guest)
on 2008-10-18 03:33
(Received via mailing list)
hiddenhippo wrote:
> however, what I also want to do is display the most recent note
> would be greatly appreciated/welcome.
This may work:

class Folder < ActiveRecord::Base
   has_one :most_recent_note, :class_name => 'Note',
           :foreign_key => :note_id, :conditions =>
           'notes.created_at = (select max(created_at) from notes)'
end

folders = Person.find(1, :include => {:folders => :most_recent_note})

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Mark J. (Guest)
on 2008-10-18 03:57
(Received via mailing list)
Mark J. wrote:
> This may work:
>
> class Folder < ActiveRecord::Base
>    has_one :most_recent_note, :class_name => 'Note',
>            :foreign_key => :note_id, :conditions =>
>            'notes.created_at = (select max(created_at) from notes)'
> end
>
> folders = Person.find(1, :include => {:folders => :most_recent_note})

Sorry, didn't think that one through properly. How about:

has_one :most_recent_note, :class_name => 'Note', :conditions => <<END
notes.id = (select max(id) from notes where notes.folder_id =
folders.id)
END

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