Rails - Oct 2004 - ActiveRecord and options_from_collection_for_select

I''m using ActiveRecord to spit out a list with find_all.  In my 
template, I''m using the options_form_collection_for_select with that 
collection and when the template loads, it''s performing a select for 
every object in the collection.  Needless to say, that''s not the most 
desirable behaviour.

So I decided I''d give caching the results a go (it''s static
data), so I
created a class variable on the ActiveRecord and wrote a method to 
lazily load the list.  It still does all the selects, and I''m guessing 
it''s because ActiveRecord grabs the data each time to make sure
it''s
not stale.

Any ideas how to a) get options_from_collection_for_select to grab all 
the rows at once or b) cache ActiveRecord results?

I''m absolutely floored by how fast I''m developing with Rails. 
Stuff
that would have taken me over a week in Java + WebWork2 + Velocity + 
Hibernate has taken me a little over a day with Rails.  I''m not even 
going to try to compare it to my current client''s project which 
requires Struts

Anoop

> Any ideas how to a) get options_from_collection_for_select to grab all 
> the rows at once or b) cache ActiveRecord results?
Depending on what data you need, it''s very likely that you can use the 
piggy-back technique: 
http://activerecord.rubyonrails.org/show/Performance

Also, do make sure that it''s actually a problem that you''re
fetching
many rows. I''ve seen people go into optimization mode on rarely used 
pages that perhaps executes 5-10 queries "too many".

That''s a waste of time! You should optimize because you need to, not 
because you don''t like the look of a few extra queries in the log. 
Optimization is excess baggage, only bring it along if you''re positive 
you''re going to need it.
> I''m absolutely floored by how fast I''m developing with
Rails.  Stuff
> that would have taken me over a week in Java + WebWork2 + Velocity + 
> Hibernate has taken me a little over a day with Rails.  I''m not
even
> going to try to compare it to my current client''s project which 
> requires Struts
That''s an awesome quote, Anoop. Thank you for saying that!
--
David Heinemeier Hansson,
http://www.basecamphq.com/   -- Web-based Project Management
http://www.rubyonrails.org/  -- Web-application framework for Ruby
http://macromates.com/       -- TextMate: Code and markup editor (OS X)
http://www.loudthinking.com/ -- Broadcasting Brain

>> Any ideas how to a) get options_from_collection_for_select to grab 
>> all the rows at once or b) cache ActiveRecord results?
>
> Depending on what data you need, it''s very likely that you can use
the
> piggy-back technique: 
> http://activerecord.rubyonrails.org/show/Performance
>
> Also, do make sure that it''s actually a problem that
you''re fetching
> many rows. I''ve seen people go into optimization mode on rarely
used
> pages that perhaps executes 5-10 queries "too many".
No doubt!  Make it work, make it work right, make it work fast.  In 
this case, though, it''s making over 100 database queries to fetch this 
select list, causing a very noticeable decrease in load time.  The 
piggy-back method isn''t really applicable since they''re all in
one
table.  I''ll try reducing it down to one find_by_sql query.  Honestly, 
the use of a select in this case is a design flaw, but I can''t think of
an alternative yet.

Another unrelated question.  Is there anything that corresponds to the 
application scope in Servlets?  Where can I toss things that I want 
everyone to have access to?  It''s stuff that really doesn''t
belong in
the database.

Also, do you know about how many users the largest rails app in 
production supports?

Anoop

> The piggy-back method isn''t really applicable since
they''re all in one
> table.  I''ll try reducing it down to one find_by_sql query. 
Honestly,
> the use of a select in this case is a design flaw, but I can''t
think
> of an alternative yet.
Interesting. Yearh, it sounds like find_by_sql is the way to go then. 
Lots of intricate relationships are best queried by straight sql.
> Another unrelated question.  Is there anything that corresponds to the 
> application scope in Servlets?  Where can I toss things that I want 
> everyone to have access to?  It''s stuff that really
doesn''t belong in
> the database.
No. Rails follows the lead of PHP in its "share nothing" policy. This 
makes Rails much easier to scale as you can push everything down to the 
database, or another service, that can then handle the concurrency 
issues.

If you really need it, I''d look into DRb. With DRb you can setup a 
separate service that can be queried from your Rails app using a 
RMI-like interface. Be sure to make that DRb service thread-safe, 
though!
> Also, do you know about how many users the largest rails app in 
> production supports?
Basecamp is the poster child for Rails. It services "tens of thousands 
of users in 40+ countries". We haven''t released any data on 
concurrency, though. So that''s more of a marketing statement than a 
technical one.
--
David Heinemeier Hansson,
http://www.basecamphq.com/   -- Web-based Project Management
http://www.rubyonrails.org/  -- Web-application framework for Ruby
http://macromates.com/       -- TextMate: Code and markup editor (OS X)
http://www.loudthinking.com/ -- Broadcasting Brain