Rails - Oct 2008 - has_many :through selections based on attributes of the :through table.

Hi all,

I''d like to get your feedback on the easiest way to find records that
are related via has_many :through based on options in the :through
table.  Suppose an Author has_many Books :through a table called
Authorships.  The Authorships table is defined as:

  create_table "authorships", :force => true do |t|
    t.belongs_to :author
    t.belongs_to :book
    t.string   "role"
  end

The "role" can either be "contributor" or "primary
author".  The model
definitions are:

class Author < Active Record::Base
  has_many :books, :through => :authorships
end

class Book < ActiveRecord::Base
  has_many :authors, :through => :authorships
end

class Authorship < ActiveRecord::Base
  belongs_to :author
  belongs_to :book
end


So supposing I have a Book, how can I find all of the authors whose
role is defined in the :through table as "contributor"?

Similarly, if I have an author, how can I find all of the books that
the author is the "primary author" of?

Thanks!
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Neal L wrote:
> Hi all,
> 
> I''d like to get your feedback on the easiest way to find records
that
> are related via has_many :through based on options in the :through
> table.  Suppose an Author has_many Books :through a table called
> Authorships.  The Authorships table is defined as:
> 
>   create_table "authorships", :force => true do |t|
>     t.belongs_to :author
>     t.belongs_to :book
>     t.string   "role"
>   end
> 
> The "role" can either be "contributor" or "primary
author".  The model
> definitions are:
> 
> class Author < Active Record::Base
>   has_many :books, :through => :authorships
> end
> 
> class Book < ActiveRecord::Base
>   has_many :authors, :through => :authorships
> end
> 
> class Authorship < ActiveRecord::Base
>   belongs_to :author
>   belongs_to :book
> end
> 
> 
> So supposing I have a Book, how can I find all of the authors whose
> role is defined in the :through table as "contributor"?
book.authors.find :all,
   :conditions => {''authorships.role'' =>
''contributor''}
> Similarly, if I have an author, how can I find all of the books that
> the author is the "primary author" of?
author.books.find :all,
   :conditions => {''authorships.role'' =>
''primary author''}


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