Rails - May 2006 - Navigation between DB Items with active Record

Hi,

I am having troubles to figure out how to move from one record to the 
other without using <find_by_sql> or other ugly tricks. So far, I have 
managed to do a lot of stuff without it but I decided that I need to 
learn how it works this weekend! So I need your help to figure that 
out...

I have the following 4 models:

class Client < ActiveRecord::Base
  has_many :client_variations
  has_many :variations, :through => :client_variations
end

class ClientVariation < ActiveRecord::Base
  belongs_to :client
  belongs_to :variation
end

class Variation < ActiveRecord::Base
  belongs_to :concept
  has_many :client_variations, :dependent => :destroy
end

class Concept < ActiveRecord::Base
    has_many :variations, :order =>"id", :dependent => :destroy
end

How can I get one of the Concept record associated with a specific 
Client? So far I have this:

temp = clients(:air_canada).variations.concept.find(:all, limit  => 1)

But I get this error:
NoMethodError: undefined method `concept'' for Variation:Class

Any help would be great because I am tired to hacking AR by using SQL 
calls..

Thanks!

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

Alain Pilon wrote:
> Hi,
>
> I am having troubles to figure out how to move from one record to the 
> other without using <find_by_sql> or other ugly tricks. So far, I
have
> managed to do a lot of stuff without it but I decided that I need to 
> learn how it works this weekend! So I need your help to figure that 
> out...
>
> I have the following 4 models:
>
> class Client < ActiveRecord::Base
>   has_many :client_variations
>   has_many :variations, :through => :client_variations
> end
>
> class ClientVariation < ActiveRecord::Base
>   belongs_to :client
>   belongs_to :variation
> end
>
> class Variation < ActiveRecord::Base
>   belongs_to :concept
>   has_many :client_variations, :dependent => :destroy
> end
>
> class Concept < ActiveRecord::Base
>     has_many :variations, :order =>"id", :dependent =>
:destroy
> end
>
> How can I get one of the Concept record associated with a specific 
> Client? So far I have this:
>
> temp = clients(:air_canada).variations.concept.find(:all, limit  => 1)
>
> But I get this error:
> NoMethodError: undefined method `concept'' for Variation:Class
>
> Any help would be great because I am tired to hacking AR by using SQL 
> calls..
>
> Thanks!
>
>   
The above is failing (I think) because

clients(:air_canada).variations

has (or could have) more than one result and therefore returns an array of
Variation objects, and is equivalent to Variation.find(:all, :conditions =>
[#some condition]).concept

Are you trying to get all concepts that belong to variations owned by air_canada
clients? If so, I''m wondering if include might help here. Something
(untested, but the console is your friend on these sorts of things) like:

temp = clients(:air_canada).variations.find(:all, :include => :concept)

If you do this query in the console it''s dump the result on screen and
you should then be able to see how to extract the concepts.

HTH

Thanks Chris,

you were right, the problem was caused by an array. I figure it out last 
night before going to bed and forgot it during the night until I saw 
your post ;-) Thanks!

Since I was only interested in getting the first Variation, I put:

first_concept = clients(:air_canada).variations[0].concept

and do an assert_not_nil to make sure it exist.

Thanks again!

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

Alain Pilon wrote:
> Thanks Chris,
>
> you were right, the problem was caused by an array. I figure it out last 
> night before going to bed and forgot it during the night until I saw 
> your post ;-) Thanks!
>
> Since I was only interested in getting the first Variation, I put:
>
> first_concept = clients(:air_canada).variations[0].concept
>
> and do an assert_not_nil to make sure it exist.
>
> Thanks again!
>
>   
No prob. I had a similar thing earlier in the week where it became clear 
after a good night''s sleep