Hi, I would like to make a relation using a different way then the classic belongs_to/has_many association. Instead of this, I would like to save the foreign key in the parent class as a list of ids. For instance, we can consider 2 models: File and Folder. Basically, we could add in File model this method: folder_id. But can we do the same with a list of file''s ids stored in this folder''s method: file_ids? Thanks -- 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 Fri, Mar 27, 2009 at 4:33 PM, Paul A. <rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:> > Hi, > > I would like to make a relation using a different way then the classic > belongs_to/has_many association. Instead of this, I would like to save > the foreign key in the parent class as a list of ids. > > For instance, we can consider 2 models: File and Folder. > Basically, we could add in File model this method: folder_id. > > But can we do the same with a list of file''s ids stored in this folder''s > method: file_ids?Once you do your has_many :files and belongs_to :folder relationships, you get folder.file_ids for free. -- Greg Donald http://destiney.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 -~----------~----~----~----~------~----~------~--~---
You could possibly do this, but why would you want to? You''ll probably want to look into the ActiveRecord docs related to virtual attributes, and possibly serialized fields. But again, WHY? The foreign key -> parent relation is practically as old as databases, and going against that current is only going to land you on TheDailyWTF... --Matt Jones On Mar 27, 5:33 pm, "Paul A." <rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:> Hi, > > I would like to make a relation using a different way then the classic > belongs_to/has_many association. Instead of this, I would like to save > the foreign key in the parent class as a list of ids. > > For instance, we can consider 2 models: File and Folder. > Basically, we could add in File model this method: folder_id. > > But can we do the same with a list of file''s ids stored in this folder''s > method: file_ids? >--~--~---------~--~----~------------~-------~--~----~ 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@googlegroups.com For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
Performance.
Lets, say you are listing a set of folders on a page and you want to
display the number of files in each folder. So you would use
something like
<%= folder.files.size() %>
With the classic foreign key relation then for every folder you will
get an SQL query like "select count(files.id) from files where
files.folder_id = ''#{folder.id}''" to determine the result
of the size
() method. This is no problem for 5 folders and a file table of a
couple of thousand records but if you are displaying 30 folders and
the file table contains 200 million records then its a performance
bottleneck. You could add an index on the files.folder_id to the
files table to speed up each search but it will still take a while.
If the ''folder.files'' element was an array of ids then there
would be
no subsequent database access to determine the size() value.
regards
damian
On Mar 29, 12:46 am, Matt Jones
<al2o...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> You could possibly do this, but why would you want to?
>
> You''ll probably want to look into the ActiveRecord docs related to
> virtual attributes, and possibly serialized fields.
>
> But again, WHY? The foreign key -> parent relation is practically as
> old as databases, and going against that current is only going to land
> you on TheDailyWTF...
>
> --Matt Jones
>
> On Mar 27, 5:33 pm, "Paul A."
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
> wrote:
>
> > Hi,
>
> > I would like to make a relation using a different way then the classic
> > belongs_to/has_many association. Instead of this, I would like to save
> > the foreign key in the parent class as a list of ids.
>
> > For instance, we can consider 2 models: File and Folder.
> > Basically, we could add in File model this method: folder_id.
>
> > But can we do the same with a list of file''s ids stored in
this folder''s
> > method: file_ids?
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damianham wrote: [...]> > If the ''folder.files'' element was an array of ids then there would be > no subsequent database access to determine the size() value.Not really true; it takes a query in either case. Your method still needs "SELECT file_ids FROM folders WHERE id = ?". That''s not really going to perform any better than "SELECT count(*) FROM files WHERE folder_id = ?", especially not if files.folder_id is indexed. If you''re really worried about performance, just cache Folder.file_ids so you don''t have to query it every time. Or you could use a nested-set tree model (there are several Rails plugins that make this easy). But storing the child keys in the parent DB record is just asking for trouble.> > regards > damianBest, -- Marnen Laibow-Koser marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org http://www.marnen.org -- 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 -~----------~----~----~----~------~----~------~--~---