Rails - Jul 2006 - Problems implementing a N:M table that contains actual data

Hi everyone,

I''m currently finishing the planning phase of a small project I want to
create.  I read a bunch of tutorials about ActiveRecord and the 
different way to link your "tables" with belongs_to, has_many, 
has_and_belong_..., etc...  However I''m stillnot sure if what
I''m trying
to do will work *well* with ActiveRecord.

So enough talk, here''s what i''m trying to do.




+-------+          +-------------+             +-----+
|clients|----------|clients_steps|-------------|steps|
+-------+          +-------------+             +-----+
                   |id           |
                   |client_id    |
                   |step_id      |
                   |completed_at |
                   +-------------+
                          |
                     +--------------+
                     |documents     |
                     +--------------+
                     |client_step_id|
                     | more         |
                     | fields       |
                     +--------------+

So we have clients, and we have steps.  Each client has a bunch of steps 
(many-to-many relationship).  The thing is each step is completed by a 
client at a certain date, which is logically stored in the clients_steps. 

Now I''ve never seen anything talking about using data from a N:M table,
I''ve only seen it used purely as associative (it''s main
purpose).  Is
there a way to easily access fields in a many to many table 
(has_and_belongs_to_many_thingy)???

Secondly, some steps require certain documents.  These documents are 
specific per step and per client.  So logically they should be attached 
to the clients_steps.  At this point I have absolutely no idea even 
where to start in Rails on how to do this.

I am new to Rails, so I need a bit of help to figure this out.  Any tip 
/ recommendation would be greatly appreciated.

Thanks,

Jd

P.S. If I have do, I''ll do pure SQL.  I''m just wondering if
there''s a
clean way to implement this in the "Rails way".

What you want is a "has_many through" association.  First, rename the 
join to something like "stepping" and create a model file for it.

class Client < ActiveRecord::Base
  has_many :steppings
  has_many :steps, :through => steppings
end

same thing for steps but wwith client instaed of steps in the has_many.

class Steppings < ActiveRecord::Base
  belongs_to :clients
  belongs_to :steps
  has_many :documents
end

Hope that helps!

-- 
Posted via http://www.ruby-forum.com/.

Thank you very much, this has helped me alot. 

Unfortunatley I''ve hit another snag.  I''ve manage to create
all my
tables through migration and now all my models seem to be working 
correctly when I play with my objects in the console.  But now, I want 
to associated all the steps to a client on creation of that client, and 
I can''t find a way to do that.

I''ve read the small many-to-many relationship tutorial at 
http://jrhicks.net/Projects/rails/has_many_and_belongs_to_many.pdf.  
Unfortunately I couldn''t get it to work properly.

Here''s what I tried (I have the models that are shown in the quoted
text
plus the Step one)
-----------------------------------------
class Step < ActiveRecord::Base
  has_many :steppings
  has_many :clients, :through => :steppings
end
-----------------------------------------
class ClientsController < ApplicationController
  <snip>...

  def new
    @client = Client.new
  end

  def create
    @client = Client.new(params[:client])

    @steps = Step.find_all  <------------------------ Here''s where
the magic
    @client.steps = @steps  <------------------------ doesn''t happen

    if @client.save
      flash[:notice] = ''Client was successfully created.''
      redirect_to :action => ''list''
    else
      render :action => ''new''
    end
  end

  <snip>...
end
-----------------------------------------------


This code would give be an error saying that Client did not have a step 
method, so I added one:
-------------------------------
class Client < ActiveRecord::Base
  <snip>...
  def steps=(new_steps)
    @steps = new_steps
  end
end
------------------------------

No more errors, but nothing in the database was added either.  I also 
tried changing the code in the controller:
@client.steps= @steps    becomes  @client.steppings = @steps

But that did not work either.  The error tells me: Expecting steppings, 
getting steps.

I am pretty lost at the moment, since I have no idea how to populate 
this association.

Any help would, once again, be greatly appreciated,

Thank you,

--
Jean-Daniel


Chris Carter wrote:
> What you want is a "has_many through" association.  First, rename
the
> join to something like "stepping" and create a model file for it.
>
> class Client < ActiveRecord::Base
>   has_many :steppings
>   has_many :steps, :through => steppings
> end
>
> same thing for steps but wwith client instaed of steps in the has_many.
>
> class Steppings < ActiveRecord::Base
>   belongs_to :clients
>   belongs_to :steps
>   has_many :documents
> end
>
> Hope that helps!
>
>