Rails - May 2006 - ActiveRecord::Associations ER diagram/macros

Hello,

I found an interesting ER diagram on the "Module:
ActiveRecord::Associations::ClassMethods" page of the Rails Framework
Documentation :
http://ar.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html

At the beginning we can read ? Associations are a set of macro-like 
class
methods for tying objects together through foreign keys. They express
relationships like "Project has one Project Manager" or "Project
belongs
to
a Portfolio". ?. I would like to learn more about that concept of 
expressing
relationships between objects. I only knew it as a design concept and 
can''t
remember seeing it applied "as this" in the source code using macros.
I
find
the idea interesting. Is it some kind of Ruby "Best Practices" or
design/development pattern ?

JM.

PS : Note that the diagram is not displayed on the "official" page :
http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html
I was only able to find it on that "mirror".

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Sorry for posting a "truncated" message but it was originally posted
on
Usenet and I forgot to rewrite it.

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Jean-Marc Molina wrote:
> At the beginning we can read ? Associations are a set of macro-like
> class methods for tying objects together through foreign keys. They
> express relationships like "Project has one Project Manager" or
> "Project belongs to a Portfolio". ?.
Reading the "Simplify Business Logic with PHP DataObjects" ONLamp.com 
article by Darryl Patterson I found an interesting comment about the 
Class::DBI [2] Perl module : ? The greatest part about it is that you 
can declare relationships between classes/tables by indicating that a 
certain column in your table either is a foreign key (has_a) or that 
your table''s primary key is referenced from another one (has_many). All
the joins will then happen behind the scenes and you can use simple 
accessors to navigate your relations. ?. The same terms as in the 
diagram are used : "has_one", "has_many"... I know these are
common
software design terms but I''m pretty sure it''s not a
co?ncidence. I''m
about to investigate on Perl communities, stay tuned...

JM.

Notes :
* [1] <http://www.onlamp.com/pub/a/php/2004/08/05/dataobjects.html>
* [2] <http://www.class-dbi.com>

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