ActiveRecord::Associations ER diagram/macros


#1

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 :


I was only able to find it on that “mirror”.


#2

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


#3

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 coïncidence. I’m
about to investigate on Perl communities, stay tuned…

JM.

Notes :