Rails - Jan 2006 - has_many - when are child objects created?

I has several model objects that flow down like a tree:

Class1 has_many Class2
Class2 has_many Class3

and so on.

when are the child records actually created?

If I do:

c1 = Class1.find(:all)

are the child objects (C2s below) created then or not until i do something like:

c2s = c1.C2s while iterating through the c1s?


If the form, that''s cool, no problem, but If I''ve got say 1000
recs in
each of the tables corresponding to the has many relationship, that
could be quite a problem, right? And I''m aware I can append columns to
an object to prevent it, but I may not want to do it that way.  When I
actually do something like c2 = c1.C2s, I will want of that attributes
of those child objects. So my question is is there a way to prevent
the relationship when you want to, even if it''s defined in the class?

thanks!


rb

Rich Brant wrote:
> I has several model objects that flow down like a tree:
> 
> Class1 has_many Class2
> Class2 has_many Class3
> 
> and so on.
> 
> when are the child records actually created?
> 
> If I do:
> 
> c1 = Class1.find(:all)
> 
> are the child objects (C2s below) created then or not until i do something
like:
> 
> c2s = c1.C2s while iterating through the c1s?
> 
> 
> If the form, that''s cool, no problem, but If I''ve got say
1000 recs in
> each of the tables corresponding to the has many relationship, that
> could be quite a problem, right? And I''m aware I can append
columns to
> an object to prevent it, but I may not want to do it that way.  When I
> actually do something like c2 = c1.C2s, I will want of that attributes
> of those child objects. So my question is is there a way to prevent
> the relationship when you want to, even if it''s defined in the
class?
By default, it''s the latter behaviour - children are loaded
''lazily'',
when referenced.

You can get eager loading of one level of children using the :include 
option in your find, e.g.

posts = Post.find(:all, :include => [ :author, :comments ])

See the section on Eager Loading in
http://ar.rubyonrails.com/classes/ActiveRecord/Associations/ClassMethods.html

regards

   Justin

> From: Rich Brant <rbrant@gmail.com>
>
> when are the child records actually created?
>
> If I do:
>
> c1 = Class1.find(:all)
>
> are the child objects (C2s below) created then or not until i do  
> something like:
>
> c2s = c1.C2s while iterating through the c1s?
>
> If the form, that''s cool, no problem, but If I''ve got say
1000 recs in
> each of the tables corresponding to the has many relationship, that
> could be quite a problem, right?
Are you observing a performance problem at the moment ?

Have you run some load testing which is indicating a performance  
problem for some future expect load ?

I realise I''m being a little facetious,  but I learned a while ago  
with Rails that everything I thought I knew about performance and  
"obvious scalability problems" was wrong.

My advice, either test/measure it and optimise, or don''t worry about  
it at all.  Guessing in advance won''t help....that way lies madness :-)

A.
--
mailto:alancfrancis@gmail.com
http://blog.alancfrancis.com/