Rails - Mar 2005 - ActiveRecord help needed

Hello, my name is Magnus and I am a RoR-newbie. I am trying to get the 
grip of ActiveRecord but I am having trouble to find good examples.

I have been looking at this:

http://wiki.rubyonrails.com/rails/show/AccessControlListExample

Where you can find this Model code:

require ''active_record''

class Permission < ActiveRecord::Base
   has_and_belongs_to_many :roles
end

class Role < ActiveRecord::Base
   has_and_belongs_to_many :permissions
   has_and_belongs_to_many :users
end

class User < ActiveRecord::Base
   has_and_belongs_to_many :roles
end

As the example says I can use:

user = User.find(1)
roles = user.roles

To get all roles for user with id 1

BUT what if I want to get all the users with all their roles and show 
them in my view. Is it possible without writing a SQL-statement?

I would like to avoid looping all the users and ask for their roles.

Br Magnus

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Magnus Hjelm wrote:
> I would like to avoid looping all the users and ask for their roles.
Then you have to write your own SQL. ActiveRecord doesn''t try to be 
overly smart - instead it gives you a nice shortcut for 90% of database 
operations and doesn''t get in the way for the remaining 10%.

Ask yourself whether or not this would be a premature optimisation though.

-- 
Best regards,

Alexey Verkhovsky

Ruby Forum: http://ruby-forum.org        (moderator)
RForum:     http://rforum.andreas-s.net  (co-author)
Instiki:    http://instiki.org           (maintainer)

> BUT what if I want to get all the users with all their roles and show
> them in my view. Is it possible without writing a SQL-statement?
> 
> I would like to avoid looping all the users and ask for their roles.
Personally, I prefer not to bang too hard on the database if I can help it.  

1) Implement caching.  Caching in Rails is very slick.  Though, it
only caches the generated HTML.  If you''ll be using the user/role data
in multiple pages, Tobi''s SimpleCache model
(http://typo.leetsoft.com/trac.cgi/file/trunk/app/models/simple_cache.rb)
works great if you''re not using CGI.

2) There''s another method that I got from EliteJournal that I explain
in a blog posting
(http://techno-weenie.net/blog/code/184/rails-best-practices).  It
would involve selecting all the roles, throwing it into a hash using
the user_id as the key, and an array of roles as the value.  Then
while looping through users, you''d access the roles like:

roles[@user.id]

I actually implemented this, but went to caching anyway.

3) There''s also the piggy backing method
(http://www.loudthinking.com/arc/000235.html), but I don''t think it
would work well for many-to-many joins.  I use this a lot in my app.

-- 
rick
http://techno-weenie.net