Rails - Dec 2005 - How to use arbitrary relationships in Activerecord

How can I ask ActiveRecord to make it''s "has_many" code to
work on some
arbitrary relationship between two tables? ie neither field is a primary key

The situation is that I am writing a Postfix management application and 
one of the tables to manage is the "alias" table.  My primary key in
the
"mailbox" table is "id", but the alias table is just a
mapping between
two text email address fields.  It needs to stay like this for 
performance reasons and also because applications querying the DB are 
not able to do table joins, finally it''s also because you can setup 
aliases for things which aren''t in your database

So I would like to be able to navigate to my "mailbox" object and then
navigate down into the "aliases" collection from that object and find 
any related aliases and also have all the nice methods that come as a 
result of using the "has_many" macro

Any suggestions?  (Or am I misunderstanding exactly what has_many 
actually does?)

Thanks

Ed W

Yeah, you could use a find_sql in the parent class and one in the child 
class.  Here is some example code.  Maybe not perfect, but the basic 
idea.  Or you could probably link the two tables together with some 
definitions in the models, but I''m not real good at that.

class Mailbox < ActiveRecord::Base
    has_many :aliases, :class_name => "Alias", :finder_sql =>
       ''SELECT * FROM aliases a, mailboxes, m WHERE a.email_address = 
m.email_address''
end

mymailbox =
Mailbox.find_by_email("railsrocks-Ijf5AnXplyJl57MIdRCFDg@public.gmane.org")
mymailbox.aliases.each do |myalias|
    puts myalias.name
end

---------------


class View < ActiveRecord::Base
    has_and_belongs_to_many :sessions
    has_many :resulting_hosts, :class_name => "Result", :finder_sql
=>
        ''SELECT DISTINCT r.host FROM results r '' +
          ''WHERE r.session_id IN '' +
             ''(SELECT s.session_id FROM sessions_views s '' +
      ''WHERE s.view_id = #{id} )''
end



Overriding Defaults

class Call < ActiveRecord::Base
    set_table_name "[HeatAdmin].[CallLog]"
    set_primary_key "CallID"
    has_many :assignments
end

Ed W wrote:
> How can I ask ActiveRecord to make it''s "has_many" code
to work on
> some arbitrary relationship between two tables? ie neither field is a 
> primary key
>
> The situation is that I am writing a Postfix management application 
> and one of the tables to manage is the "alias" table.  My primary
key
> in the "mailbox" table is "id", but the alias table is
just a mapping
> between two text email address fields.  It needs to stay like this for 
> performance reasons and also because applications querying the DB are 
> not able to do table joins, finally it''s also because you can
setup
> aliases for things which aren''t in your database
>
> So I would like to be able to navigate to my "mailbox" object and
then
> navigate down into the "aliases" collection from that object and
find
> any related aliases and also have all the nice methods that come as a 
> result of using the "has_many" macro
>
> Any suggestions?  (Or am I misunderstanding exactly what has_many 
> actually does?)
>
> Thanks
>
> Ed W
> _______________________________________________
> Rails mailing list
> Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>
>
>

Charles Leeds wrote:
> Yeah, you could use a find_sql in the parent class and one in the 
> child class.  Here is some example code.  Maybe not perfect, but the 
> basic idea.  Or you could probably link the two tables together with 
> some definitions in the models, but I''m not real good at that.
>
> class Mailbox < ActiveRecord::Base
>    has_many :aliases, :class_name => "Alias", :finder_sql
=>
>       ''SELECT * FROM aliases a, mailboxes, m WHERE a.email_address
=
> m.email_address''
> end
>
> mymailbox =
Mailbox.find_by_email("railsrocks-Ijf5AnXplyJl57MIdRCFDg@public.gmane.org")
> mymailbox.aliases.each do |myalias|
>    puts myalias.name
> end
>
This is excellent (and obvious now it''s written down).  Thanks

What happens during "saving" though?  Is it possible to append new 
objects to mymailbox.aliases and then save them back to the database 
correctly?  This was one thing I wasn''t sure about when deviating from 
the standard relationships?

Thanks very much for taking the time to respond

Ed W