Rails - Feb 2007 - Viewing object associated via "has_many :through"?

This is my first question to the Forum. I’ve set up these associations:

class Playlist < ActiveRecord::Base
  …
  has_many :playlists_tracks, :dependent => :destroy
  has_many :track_ones, :through => :playlists_tracks, :source => :track
  has_many :track_twos, :through => :playlists_tracks, :source => :track
end

class Track < ActiveRecord::Base
  …
  has_many :playlists_tracks, :dependent => :destroy
  has_many :playlists, :through => :playlists_tracks
  has_many :playlists, :through => :playlists_tracks
end

class PlaylistsTrack < ActiveRecord::Base
  belongs_to :playlist
  belongs_to :track_one, :class_name => :track, :foreign_key =>
''track_one_id''
  belongs_to :track_two, :class_name => :track, :foreign_key =>
''track_two_id''
end

With them I’m able to save to the playlists_tracks table the following:
id, playlist_id, track_one_id, track_two_id. That all seems to work
fine.

But no matter what I put in my playlists/show view file, I get an error
message when I attempt to view the tracks associated with a playlist.
For example:

<% for track in @playlist.tracks %>

<tr>
<td><%= playlist.track_one.title %></td>
</tr>

<% end %>

gets me this:

undefined method `tracks'' for #<Playlist:0xeb4a380>

I think the problem revolves around the "class_name" and
"source"
options, as I have no problem displaying the name of the Playlistcreator
(who is also associated with Playlist through a "has many :through"
association, but without the “class_name” and “source” options) via the
playlists/show view.

Where am I going wrong? What do I need to do to fix this?

-- 
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@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---

You want to use @playlists.playlists_tracks in your view ...

On Feb 5, 1:05 pm, Christian Braun
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
> This is my first question to the Forum. I''ve set up these
associations:
>
> class Playlist < ActiveRecord::Base
>   ...
>   has_many :playlists_tracks, :dependent => :destroy
>   has_many :track_ones, :through => :playlists_tracks, :source =>
:track
>   has_many :track_twos, :through => :playlists_tracks, :source =>
:track
> end
>
> class Track < ActiveRecord::Base
>   ...
>   has_many :playlists_tracks, :dependent => :destroy
>   has_many :playlists, :through => :playlists_tracks
>   has_many :playlists, :through => :playlists_tracks
> end
>
> class PlaylistsTrack < ActiveRecord::Base
>   belongs_to :playlist
>   belongs_to :track_one, :class_name => :track, :foreign_key =>
> ''track_one_id''
>   belongs_to :track_two, :class_name => :track, :foreign_key =>
> ''track_two_id''
> end
>
> With them I''m able to save to the playlists_tracks table the
following:
> id, playlist_id, track_one_id, track_two_id. That all seems to work
> fine.
>
> But no matter what I put in my playlists/show view file, I get an error
> message when I attempt to view the tracks associated with a playlist.
> For example:
>
> <% for track in @playlist.tracks %>
>
> <tr>
> <td><%= playlist.track_one.title %></td>
> </tr>
>
> <% end %>
>
> gets me this:
>
> undefined method `tracks'' for #<Playlist:0xeb4a380>
>
> I think the problem revolves around the "class_name" and
"source"
> options, as I have no problem displaying the name of the Playlistcreator
> (who is also associated with Playlist through a "has many
:through"
> association, but without the "class_name" and "source"
options) via the
> playlists/show view.
>
> Where am I going wrong? What do I need to do to fix this?
>
> --
> Posted viahttp://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
-~----------~----~----~----~------~----~------~--~---

Bill Siggelkow wrote:
> You want to use @playlists.playlists_tracks in your view ...
Thank you Bill!

That has got me a step further. This in the view, for example:

<% for track_one in @playlist.playlists_tracks %>

<tr>
<td><%= track_one.id %></td>
</tr>

<% end %>

now displays the track_one.id, which is a good sign.

But I still can''t reach beyond the playlists_tracks join table to pull 
the title of the track from the tracks table itself. I need the
"title"
of the track where the "track.id" is the same as the
"track_one.id". I
think I need a trick to kind of weave through the ":source" and 
":class_name" options to get to the tracks table, but maybe
I''m missing
something obvious here. Any ideas?

Again, many thanks for your answer.


-- 
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
-~----------~----~----~----~------~----~------~--~---

I think what you need to do is leverage your has_many :through
relationship. Something like:

<% for track in @playlist.track_ones %>
  <tr>
  <td><%= track.title %></td>
 </tr>
<% end %>

or more idiomatically

<% @playlist.track_ones.each do |track| %>
  <tr>
  <td><%= track.title %></td>
 </tr>
<% end %>

I don''t know your data model, however, the "track_ones" thing
kind of
smells a bit of an incorrect data model. In general, if you have a
table
that enumerates a set of columns (track_1, track_2, ...) it may
indicate that you are not modeling a parent -> child relationship. It
was just a thought ... I am probably barking up the wrong tree ...


On Feb 5, 3:26 pm, Christian Braun
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
> Bill Siggelkow wrote:
> > You want to use @playlists.playlists_tracks in your view ...
>
> Thank you Bill!
>
> That has got me a step further. This in the view, for example:
>
> <% for track_one in @playlist.playlists_tracks %>
>
> <tr>
> <td><%= track_one.id %></td>
> </tr>
>
> <% end %>
>
> now displays the track_one.id, which is a good sign.
>
> But I still can''t reach beyond the playlists_tracks join table to
pull
> the title of the track from the tracks table itself. I need the
"title"
> of the track where the "track.id" is the same as the
"track_one.id". I
> think I need a trick to kind of weave through the ":source" and
> ":class_name" options to get to the tracks table, but maybe
I''m missing
> something obvious here. Any ideas?
>
> Again, many thanks for your answer.
>
> --
> Posted viahttp://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
-~----------~----~----~----~------~----~------~--~---

Bill Siggelkow wrote:
> I think what you need to do is leverage your has_many :through
> relationship. Something like:
> 
> <% for track in @playlist.track_ones %>
>   <tr>
>   <td><%= track.title %></td>
>  </tr>
> <% end %>
Thanks again. I''d already tried that and got this error message:

Could not find the source association(s) :track in model PlaylistsTrack. 
Try ''has_many :track_ones, :through => :playlists_tracks, :source
=>
<name>''.  Is it one of :track_two, :playlist, or :track_one?

I''ve been through all the different variants I can think of (like the 
odd one in my original example), but they all throw up an error message. 
I tried acting on the error message I just listed, but didn''t get 
anywhere with it. Can you or anyone see any wisdom in it that''ll help 
me?
> I don''t know your data model, however, the "track_ones"
thing kind of
> smells a bit of an incorrect data model. 
Bad choice of name, I agree. It just refers to which position in the 
form the track was selected at, and that''s arbitrary, non-essential 
information. I''ll have a think about that, though, as people
don''t tend
to give their kids ordinals as names, and you may be right. But even if 
my model is a bit skewed, I think I''d be having the same problem with 
"jazz_tracks" and "rock_tracks", etc.

Can you or anyone else think what the problem might be? I''m pretty sure
it relates to the ":source" and ":class_name" options.
Again, I have no
problem saving all the relevant data to the playlists_tracks join table, 
but then can''t access the tracks table afterward to grab the track
name.

-- 
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
-~----------~----~----~----~------~----~------~--~---

I believe that Rails uses the :source to identify the foreign key in
the join table for the :through relationship. Try this ...

class Playlist < ActiveRecord::Base
  ...
  has_many :playlists_tracks, :dependent => :destroy
  has_many :track_ones, :through => :playlists_tracks, :source
=> :track_one
  has_many :track_twos, :through => :playlists_tracks, :source
=> :track_two
end

Then use the your :through relationships in the view as before ..


On Feb 5, 4:55 pm, Christian Braun
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
> Bill Siggelkow wrote:
> > I think what you need to do is leverage your has_many :through
> > relationship. Something like:
>
> > <% for track in @playlist.track_ones %>
> >   <tr>
> >   <td><%= track.title %></td>
> >  </tr>
> > <% end %>
>
> Thanks again. I''d already tried that and got this error message:
>
> Could not find the source association(s) :track in model PlaylistsTrack.
> Try ''has_many :track_ones, :through => :playlists_tracks,
:source =>
> <name>''.  Is it one of :track_two, :playlist, or :track_one?
>
> I''ve been through all the different variants I can think of (like
the
> odd one in my original example), but they all throw up an error message.
> I tried acting on the error message I just listed, but didn''t get
> anywhere with it. Can you or anyone see any wisdom in it that''ll
help
> me?
>
> > I don''t know your data model, however, the
"track_ones" thing kind of
> > smells a bit of an incorrect data model.
>
> Bad choice of name, I agree. It just refers to which position in the
> form the track was selected at, and that''s arbitrary,
non-essential
> information. I''ll have a think about that, though, as people
don''t tend
> to give their kids ordinals as names, and you may be right. But even if
> my model is a bit skewed, I think I''d be having the same problem
with
> "jazz_tracks" and "rock_tracks", etc.
>
> Can you or anyone else think what the problem might be? I''m pretty
sure
> it relates to the ":source" and ":class_name" options.
Again, I have no
> problem saving all the relevant data to the playlists_tracks join table,
> but then can''t access the tracks table afterward to grab the track
name.
>
> --
> Posted viahttp://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
-~----------~----~----~----~------~----~------~--~---

Yes, you''re right!

With this model (like you said):

class Playlist < ActiveRecord::Base
  ...
  has_many :playlists_tracks, :dependent => :destroy
  has_many :track_ones, :through => :playlists_tracks, :source
=> :track_one
  has_many :track_twos, :through => :playlists_tracks, :source
=> :track_two
end

And this in the playlists/show view:

<% for track_one in @playlist.track_ones %>

<tr>
<td><%= track_one.title %></td>
</tr>

<% end %>

I can display the track''s name.

Bill, Thank you so much! I really appreciate your walking me and my
noobishness through this. I can now link the last pieces of my
application together, and that''s a great relief. Cheers!




--~--~---------~--~----~------------~-------~--~----~
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
-~----------~----~----~----~------~----~------~--~---