Rails - Feb 2005 - cant map foreign key in list view

Hi

I have been struggling to get a foreign key in a list map to a readable
value in a lookup table

 

I have a list of projects and each project has a project_manager. 

 

Project.rb

class Project < ActiveRecord::Base

    has_one :project_manager, :class_name => "Users", :foreign_key
=>
"manager_id"

end

 

The association above sais that a project_manager is in fact just a
User. BTW what is the technical term for the project_manager object?

 

The Project DB table has a foreign key column called manager_id and the
Users table has a id column. Based on this Rails should be able to put
project.manager_id = users.id in the SQL where clause (I hope)

 

Rails should now allow me to do something like:-

 

Projects_controller.rb

def list

    @projects = Project.find_all

end

  

list.rhtml

<% @projects.each do |project| %>

  <tr>

   <td><%= project.project_manager.firstname %></td>

  </tr>

 <% end %>

 

But I get an error:-

Showing /projects/list.rhtml where line #35 raised
c:/ruby/lib/ruby/gems/1.8/gems/actionpack-1.4.0/lib/action_controller/su
pport/dependencies.rb:59:in `const_missing'': uninitialized constant
Users 

32: 
33:  <% @projects.each do |project| %>
34:   <tr>
35:    <td><%= project.project_manager.firstname %></td>
36:   </tr>
37:  <% end %>
38: 

 

What am I doing wrong? BTW why is there no @ in front of project but
there is for @projects?

 

Also if the above concept can be made to work then I suppose it could be
quite heavy since it must be doing a single select for each project to
get the manager info. Or is this done relationally in the controller
based on the Model definitions.

 

Thanks

Peter <http://127.0.0.1:3000/projects/list> 



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Hi Peter,
> Project.rb
>
> class Project < ActiveRecord::Base
>
>     has_one :project_manager, :class_name => "Users",
:foreign_key =>
> "manager_id"
>
> end
I think you are talking about a one-to-many relationship here. One  
project has one project manager but one user can be a project manager  
in many projects (old and new).

In that case, you need to add ''has_many :project_in_leads, :class_name
=> "Project", :foreign_key => "manager_id" ''
to your User class.

Actually, that isn''t necessary if you never want to approach projects  
from the user perspective ("Which projects has this guy lead?").

But anyway, you need to use belongs_to instead of has_one in your  
Project class. If you use has_one, it means that the foreign key field  
is on the other side of the relationship (i.e. in users table), which  
isn''t the case here.

So consider changing the line to ''belongs_to :project_manager,  
:class_name => "User", :foreign_key => "manager_id"
'' .

> But I get an error:-
>
> Showing /projects/list.rhtml where line #35 raised  
> c:/ruby/lib/ruby/gems/1.8/gems/actionpack-1.4.0/lib/action_controller/ 
> support/dependencies.rb:59:in `const_missing'': uninitialized
constant
> Users
This is because you have ":class_name => "Users"" in
Project class
(should be "User"). But you also need to do the changes above to make
it work right.
> Also if the above concept can be made to work then I suppose it could  
> be quite heavy since it must be doing a single select for each project  
> to get the manager info. Or is this done relationally in the  
> controller based on the Model definitions.
I think it will be repeated for every row. You can inspect the queries  
by looking at the development.log (assuming you''re in dev state) in  
your application''s log folder.

//jarkko

--
Jarkko Laine
http://jlaine.net
http://odesign.fi



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