Rails - Apr 2005 - has_one/belongs_to and rails modeling questions...

from the docs:

Both express a 1-1 relationship, the difference is mostly where to place 
the foreign key, which goes on the table for the class saying 
belongs_to. Example:

  class Post < ActiveRecord::Base
    has_one :author
  end

  class Author < ActiveRecord::Base
    belongs_to :post
  end

The tables for these classes could look something like:

  CREATE TABLE posts (
    id int(11) NOT NULL auto_increment,
    title varchar default NULL,
    PRIMARY KEY  (id)
  )

  CREATE TABLE authors (
    id int(11) NOT NULL auto_increment,
    post_id int(11) default NULL,
    name varchar default NULL,
    PRIMARY KEY  (id)
  )

so far i follow...

but what if i wanted to do something like...

a show occurs at a venue
a venue can have many shows...

so i have

shows
  venue_id
  etc.

venue
  etc.

so a show belongs_to venue
and what a venue has_many shows

again from the docs...

One-to-one associations

    * Assigning an object to a has_one association automatically saves 
that object, and the object being replaced (if there is one), in order 
to update their primary keys - except if the parent object is unsaved 
(new_record? == true).
    * If either of these saves fail (due to one of the objects being 
invalid) the assignment statement returns false and the assignment is 
cancelled.
    * If you wish to assign an object to a has_one association without 
saving it, use the association.build method (documented below).
    * Assigning an object to a belongs_to association does not save the 
object, since the foreign key field belongs on the parent. It does not 
save the parent either.

    * Adding an object to a collection (has_many
     
<http://api.rubyonrails.com/classes/ActiveRecord/Associations/ClassMethods.html#M000433>
      or has_and_belongs_to_many
     
<http://api.rubyonrails.com/classes/ActiveRecord/Associations/ClassMethods.html#M000436>)
      automatically saves that object, except if the parent object (the
      owner of the collection) is not yet stored in the database.
    * If saving any of the objects being added to a collection (via push
      or similar) fails, then push returns false.
    * You can add an object to a collection without automatically saving
      it by using the collection.build method (documented below).
    * All unsaved (new_record? == true) members of the collection are
      automatically saved when the parent is saved.


so if i did something like venue.shows[10] = show
then the show object gets saved correct?

but show.venue = venue
doesnt result in the venue object getting saved correct?

want to make sure i am reading everything right...


If i have that part right how then do you do something like the following

you have an entity which can have many contact information entries
( similarly a contact info belongs_to an entity )

an entity is either a company or a person so we have a type field to 
distinguish

if a customer in an oo sense is a person but in sql is:

CREATE TABLE customers
(
id
entity_id
... additional information above and beyond what defines an entity...
)

how with rails do you represent something as convoluted as this?








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Sean T Allen <sean-5W9FBhQXBOtBDgjK7y7TUQ@public.gmane.org> writes:
> you have an entity which can have many contact information entries
> ( similarly a contact info belongs_to an entity )
>
> an entity is either a company or a person so we have a type field to 
> distinguish
>
> if a customer in an oo sense is a person but in sql is:
>
> CREATE TABLE customers
> (
> id
> entity_id
> ... additional information above and beyond what defines an entity...
> )
>
> how with rails do you represent something as convoluted as this?
class Entity < ActiveRecord::Base; end

class Company < Entity; end

class Person < Entity; end

class Customer < Person; end

What your describing doesn''t sound like object relationships to me,
but rather object hierarchy.  I haven''t figured out how to allow the
Entity class above to be abstract; so you''d need an entity table with
nearly nothing in it.  Maybe you could go ahead and put the common
data in there between companies and people.  Depending on your data, I
might consider making companies and people separate tables; but it
sounds like customers and people could use STI.  I don''t really have
enough to go on though; maybe companies, people, and customers could
go in the same table with STI.
-- 
doug-jGAhs73c5XxeoWH0uzbU5w@public.gmane.org