Help for newbie please! I have two tables: controls and programs. controls has_many :programs Programs belongs_to :control Controls has id, controlname Programs has, apart from it''s own id, two fields ctl1_id and ctl2_id. These represent two controls that the program relates to. Foreign keys are set on program table columns ctl1_id and ctl2_id back to the id field on the control table. So when I list the program table using <% @programs.each do |array| %> <tr> <td><%= array.ctl1_id%></td> <td><%= array.ctl2_id %></td> </tr> <% end %> ...everything is fine. But when I list the programs row I want to actually show the controlname from controls table rather than the ctl1_id and ctl2_id values from the programs row. For this I use the following code:- <% @programs.each do |array| %> <tr> <td><%= array.control.controlname %></td> <td><%= array.control.controlname %></td> </tr> <% end %> I expect the link via the foreign keys and the models relationships to give me what I need but I am obviously missing something because I get this:-. You have a nil object when you didn''t expect it! The error occured while evaluating nil.control Extracted source (around line #56): 53: </tr> 54: <tr> 55: 56: <%= array.control.controlname %></td> I have checked out the cookbook application code and cant see where I am misunderstanding. Any help gratefully received. Thanks I can see that -- 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 May 25, 2007, at 11:24 AM, Martyn Elmy-liddiard wrote:> Help for newbie please! > > I have two tables: controls and programs. > > controls has_many :programs > Programs belongs_to :control > > Controls has id, controlname > Programs has, apart from it''s own id, two fields ctl1_id and ctl2_id. > > These represent two controls that the program relates to. > > Foreign keys are set on program table columns ctl1_id and ctl2_id back > to the id field on the control table.Let''s make this more explicit: class Control < ActiveRecord::Base has_many :programs end class Program < ActiveRecord::Base belongs_to :ctl1, :class_name => ''Control'', :foreign_key => ''ctl1_id'' belongs_to :ctl2, :class_name => ''Control'', :foreign_key => ''ctl2_id'' end> So when I list the program table using > > <% @programs.each do |array| %> > <tr> > <td><%= array.ctl1_id%></td> > <td><%= array.ctl2_id %></td> > </tr> > <% end %> > > ...everything is fine.Any of these: <% @programs.each do |program| %> <% @programs.each do |p| %> <% for program in @programs %> is probably better than "array" for the block variable. (But this is a personal choice as long as you avoid keywords like "class" or "begin".)> But when I list the programs row I want to actually show the > controlname > from controls table rather than the ctl1_id and ctl2_id values from > the > programs row. For this I use the following code:- > > <% @programs.each do |array| %> > <tr> > <td><%= array.control.controlname %></td> > <td><%= array.control.controlname %></td> > </tr> > <% end %> > > I expect the link via the foreign keys and the models relationships to > give me what I need but I am obviously missing something because I get > this:-. > > You have a nil object when you didn''t expect it! > The error occured while evaluating nil.control > > Extracted source (around line #56): > > 53: </tr> > 54: <tr> > 55: > 56: <%= array.control.controlname %></td> > > I have checked out the cookbook application code and cant see where > I am > misunderstanding. > > Any help gratefully received. > > Thanks > > > I can see that > > --<% @programs.each do |program| %> <tr> <td><%= program.ctl1.controlname %></td> <td><%= program.ctl2.controlname %></td> </tr> <% end %> But personally, I''d rename "controlname" to just "name" since it''s a column in the Control model anyway. From this little example, it seems like you have a program with many (ok, 2) controls, but does each control really associate to more than one program? I''m just wondering whether there''s another join model linking programs and controls in a many-to-many relationship. Anyway, I suspect that you are under the mistaken assumption that the existence of foreign keys in the database have some influence on the behavior of your ActiveRecord models. Other than potentially causing inserts or deletes to fail if performed in the wrong order, your Models won''t care. -Rob Rob Biedenharn http://agileconsultingllc.com Rob-xa9cJyRlE0mWcWVYNo9pwxS2lgjeYSpx@public.gmane.org --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
Rob,
Thanks very much for bothering to help a newbie.
I was indeed under the mistaken assumption that the existence of foreign
keys in the database influence the behavior of your ActiveRecord models.
I now see it''s the model.
I have taken your suggestion and it now works! - many thanks but I do
have a follow-up, if I may:-
To further explain my structure:
The control table actually has say 10 rows (i.e. there are 10 potential
controls.)
The program table has columns ctl1_id, ctl2_id....through ctl10_id.)
So a program can have upto 10 controls that are relevant to it.
Taking your help I now have:-
class Program < ActiveRecord::Base
belongs_to :ctl1, :class_name => ''Control'',
:foreign_key => ''ctl1''
belongs_to :ctl2, :class_name => ''Control'',
:foreign_key => ''ctl2''
belongs_to :ctl3, :class_name => ''Control'',
:foreign_key => ''ctl3''
belongs_to :ctl4, :class_name => ''Control'',
:foreign_key => ''ctl4''
belongs_to :ctl5, :class_name => ''Control'',
:foreign_key => ''ctl5''
belongs_to :ctl6, :class_name => ''Control'',
:foreign_key => ''ctl6''
belongs_to :ctl7, :class_name => ''Control'',
:foreign_key => ''ctl7''
belongs_to :ctl8, :class_name => ''Control'',
:foreign_key => ''ctl8''
belongs_to :ctl9, :class_name => ''Control'',
:foreign_key => ''ctl9''
belongs_to :ctl10, :class_name => ''Control'',
:foreign_key => ''ctl10''
end
and.....
<% @programs.each do |program| %>
<table>
<tr>
<td><%= program.ctl1.control %></td>
<td><%= program.ctl2.control %></td>
<td><%= program.ctl3.control %></td>
<td><%= program.ctl4.control %></td>
<td><%= program.ctl5.control %></td>
<td><%= program.ctl6.control %></td>
<td><%= program.ctl7.control %></td>
<td><%= program.ctl8.control %></td>
<td><%= program.ctl9.control %></td>
<td><%= program.ctl10.control %></td>
</tr>
<%end>
...this is great but I now have a related issue in that if I list the
controls related to a program with all 10 nominated it fine but if I
list the controls related to a program with say 7 controls nominated
then the code falls over on the first ''empty'' reference.
i.e. <%= program.ctl8.control %> returns an error:-
You have a nil object when you didn''t expect it!
The error occured while evaluating nil.control
Is there a way to code round this ''empty'' reference?
Much appreciated!
Martyn
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this is clearly an example of a many-to-many relationship, an not a
one-to-many relationship as you tried to do with has_many and
belongs_to
A Control can have one or more Programs, and a Program can belong to
one or more controls.
use has_many :through or has_and_belong_to_many
#Tables:
controls:
id, controlname
programs
id, name
controls_programs
control_id, program_id
the last table maps the many-to-many relationship between Controls and
Programs
#Models:
Control < ActiveRecord::Base
has_and_belongs_to_many :programs
end
Control < ActiveRecord::Base
has_and_belongs_to_many :controls
end
#controller:
@programs = Program.find :all, :include => "controls"
#view
<% @programs.each do |program| %>
<% program.controls.each do |control| %>
<tr>
<%= control.controlname %>
</tr>
<% end %>
<% end %>
On 29 Mai, 13:57, Martyn Elmy-liddiard <rails-mailing-l...@andreas-
s.net> wrote:> Rob,
>
> Thanks very much for bothering to help a newbie.
>
> I was indeed under the mistaken assumption that the existence of foreign
> keys in the database influence the behavior of your ActiveRecord models.
> I now see it''s the model.
>
> I have taken your suggestion and it now works! - many thanks but I do
> have a follow-up, if I may:-
>
> To further explain my structure:
>
> The control table actually has say 10 rows (i.e. there are 10 potential
> controls.)
> The program table has columns ctl1_id, ctl2_id....through ctl10_id.)
>
> So a program can have upto 10 controls that are relevant to it.
>
> Taking your help I now have:-
> class Program < ActiveRecord::Base
> belongs_to :ctl1, :class_name => ''Control'',
:foreign_key => ''ctl1''
> belongs_to :ctl2, :class_name => ''Control'',
:foreign_key => ''ctl2''
> belongs_to :ctl3, :class_name => ''Control'',
:foreign_key => ''ctl3''
> belongs_to :ctl4, :class_name => ''Control'',
:foreign_key => ''ctl4''
> belongs_to :ctl5, :class_name => ''Control'',
:foreign_key => ''ctl5''
> belongs_to :ctl6, :class_name => ''Control'',
:foreign_key => ''ctl6''
> belongs_to :ctl7, :class_name => ''Control'',
:foreign_key => ''ctl7''
> belongs_to :ctl8, :class_name => ''Control'',
:foreign_key => ''ctl8''
> belongs_to :ctl9, :class_name => ''Control'',
:foreign_key => ''ctl9''
> belongs_to :ctl10, :class_name => ''Control'',
:foreign_key => ''ctl10''
> end
>
> and.....
>
> <% @programs.each do |program| %>
> <table>
> <tr>
> <td><%= program.ctl1.control %></td>
> <td><%= program.ctl2.control %></td>
> <td><%= program.ctl3.control %></td>
> <td><%= program.ctl4.control %></td>
> <td><%= program.ctl5.control %></td>
> <td><%= program.ctl6.control %></td>
> <td><%= program.ctl7.control %></td>
> <td><%= program.ctl8.control %></td>
> <td><%= program.ctl9.control %></td>
> <td><%= program.ctl10.control %></td>
> </tr>
> <%end>
>
> ...this is great but I now have a related issue in that if I list the
> controls related to a program with all 10 nominated it fine but if I
> list the controls related to a program with say 7 controls nominated
> then the code falls over on the first ''empty'' reference.
>
> i.e. <%= program.ctl8.control %> returns an error:-
>
> You have a nil object when you didn''t expect it!
> The error occured while evaluating nil.control
>
> Is there a way to code round this ''empty'' reference?
>
> Much appreciated!
>
> Martyn
>
> --
> Posted viahttp://www.ruby-forum.com/.
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Thorsten Thanks for your detailed coding help. Unfortunately I am still failing to get this to work - probably missing a key point....soooo frustrating! I have, as advised, create the controls_programs table, changed the models as advised, changed the controller code and added the view code.> > #controller: > @programs = Program.find :all, :include => "controls" > > #view > <% @programs.each do |program| %> > <% program.controls.each do |control| %> > <tr> > <%= control.controlname %> > </tr> > <% end %> > <% end %> >I get the program rows returned as before but still get no control rows returned. I know helping newbies can be hard-work but if you have any ideas do please let me know. In the meantime I''ll keep plugging away...I might just get it! Thanks Martyn -- 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 -~----------~----~----~----~------~----~------~--~---
Well, just changing the code doesn''t do the trick ... do you have associated the programs with the controls? tables: #programs #controls_programs #controls id 1 program_id 1 id 2 name TestProg control_id 2 controlname TestControl now controls_programs has an entry that reraltes Program 1 with Control 2 You achive that like this in your controller: class Program < ActionController::Base def add_control @program = Program.find(1) @control = Control.find(1) @program.controls << @control end The your programs and controls are really associated and the view code should work You can read more about that here: http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html http://wiki.rubyonrails.org/rails/pages/has_and_belongs_to_many also have a look at "has_many :through =>" (google will help) which is a "better" has_and_belongs_to_many ... Hope that helps On 30 Mai, 17:00, Martyn Elmy-liddiard <rails-mailing-l...@andreas- s.net> wrote:> Thorsten > > Thanks for your detailed coding help. > > Unfortunately I am still failing to get this to work - probably missing > a key point....soooo frustrating! > > I have, as advised, create the controls_programs table, changed the > models as advised, changed the controller code and added the view code. > > > #controller: > > @programs = Program.find :all, :include => "controls" > > > #view > > <% @programs.each do |program| %> > > <% program.controls.each do |control| %> > > <tr> > > <%= control.controlname %> > > </tr> > > <% end %> > > <% end %> > > I get the program rows returned as before but still get no control rows > returned. I know helping newbies can be hard-work but if you have any > ideas do please let me know. In the meantime I''ll keep plugging away...I > might just get it! > > Thanks > > Martyn > > -- > 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 -~----------~----~----~----~------~----~------~--~---
Thorsten Thnaks very much for bothering to help once again. Hurrah! I now get it and it''s all working fine. V.Much appreciated. One final question please; I had to manually load the data into the controls_programs table; Should the rails framework do this automatically based on adding a record to the programs table and specifying the controls it relates to? Martyn -- 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 already gave you an example in my previous post about how to add a relationship between a program and a control: #controller def add_control_to_program @program = Program.find(params[:program_id]) @control = Control.find(params[:control_id]) @program.controls << @control @program.save end Rails then adds the corrept mapping line into the controls_programs table You can also do it vice versa, like: @control.porgrams << @porgram the result is the same because of the nature of the many-to-many relationship for more info read the API Docs about associations please, i already gave you the links in my previous post. On 31 Mai, 17:46, Martyn Elmy-liddiard <rails-mailing-l...@andreas- s.net> wrote:> Thorsten > > Thnaks very much for bothering to help once again. > > Hurrah! I now get it and it''s all working fine. > > V.Much appreciated. > > One final question please; I had to manually load the data into the > controls_programs table; Should the rails framework do this > automatically based on adding a record to the programs table and > specifying the controls it relates to? > > Martyn > > -- > 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 -~----------~----~----~----~------~----~------~--~---