Rails - Jan 2006 - categories/recipes & books/descriptions - has_many vs has_one => id question

People,

In the cookbook eg, categories has_many recipes but in a book eg, book
has_one description - doesn''t that mean that the id of the description
should be the same as the id of the book (instead of having it''s own
"description_id" in the book table?

Thanks,

Phil.
-- 
Philip Rhoades

Pricom Pty Limited  (ACN 003 252 275  ABN 91 003 252 275)
GPO Box 3411
Sydney NSW      2001
Australia
Mobile:  +61:(0)411-185-652
Fax:     +61:(0)2-8221-9599
E-mail:  phil@pricom.com.au

On 1/18/06, Philip Rhoades <phil@pricom.com.au>
wrote:
> People,
>
> In the cookbook eg, categories has_many recipes but in a book eg, book
> has_one description - doesn''t that mean that the id of the
description
> should be the same as the id of the book (instead of having it''s
own
> "description_id" in the book table?
>
The category -> recipes tables look like this:
categories
-id
-other_stuff

recipes
-id
-category_id
-other_stuff

The book -> description relationship implies this kind of setup:
books
-id
-title
-other_stuff

descriptions
-id
-book_id
-description_text

class Book
has_one :description #Note the singular, rather than plural.
end

class Description
belongs_to :book
end

@book = Book.find(:first)

@book.description returns the instance of Description that was
associated with that book.

In a typical setup, every ActiveRecord class (Book, Description, etc)
maps to a database table, and that table has an ''id'' column
for the
primary key.  Descriptions each have a unique id independent of their
Book.

Wilson,

Thanks for that - but I am still unclear - if there is _only_ one
description per book, isn''t it unnecessary to have a field
"book_id" for
descriptions? (ie book id = description id).  This is what I would do if
I were managing this manually.  I guess it is keep the automatic
scaffolding stuff consistent?

Regards,

Phil.


On Wed, 2006-01-18 at 13:56 -0500, Wilson Bilkovich
wrote:
> On 1/18/06, Philip Rhoades <phil@pricom.com.au> wrote:
> > People,
> >
> > In the cookbook eg, categories has_many recipes but in a book eg, book
> > has_one description - doesn''t that mean that the id of the
description
> > should be the same as the id of the book (instead of having
it''s own
> > "description_id" in the book table?
> >
> 
> The category -> recipes tables look like this:
> categories
> -id
> -other_stuff
> 
> recipes
> -id
> -category_id
> -other_stuff
> 
> The book -> description relationship implies this kind of setup:
> books
> -id
> -title
> -other_stuff
> 
> descriptions
> -id
> -book_id
> -description_text
> 
> class Book
> has_one :description #Note the singular, rather than plural.
> end
> 
> class Description
> belongs_to :book
> end
> 
> @book = Book.find(:first)
> 
> @book.description returns the instance of Description that was
> associated with that book.
> 
> In a typical setup, every ActiveRecord class (Book, Description, etc)
> maps to a database table, and that table has an ''id''
column for the
> primary key.  Descriptions each have a unique id independent of their
> Book.
> 
-- 
Philip Rhoades

Pricom Pty Limited  (ACN 003 252 275  ABN 91 003 252 275)
GPO Box 3411
Sydney NSW      2001
Australia
Mobile:  +61:(0)411-185-652
Fax:     +61:(0)2-8221-9599
E-mail:  phil@pricom.com.au