How does ActiveRecord do it?

[Ralph Shnelvar]

I know it sounds like a Rails question ... but it isn't.

Consider
irb(main):001:0> class X
irb(main):002:1> puts "Hi"
irb(main):003:1> end
Hi
=> nil
irb(main):004:0> x = X.new
=> #<X:0x42458ac>

The "Hi" is sent to stdout as the class X is parsed. (Well, after the
end statement.) Right?

"Hi" is not generated when a new instance of X is created ... right?



So now consider
# in .\app\models\user.rb
class X < ActiveRecord::Base
puts "Hi 2"
end


"Hi 2" gets displayed by webrick every time I generate a form.

How does this happen? Is webrick(?) reloading .\app\models\user.rb every
time a form is generated?



(And now a Rails question ...)

Assuming it is reloading .\app\models\user.rb in development mode ...
will it do this in production mode?

 

[Matt H]

Is webrick(?) reloading .\app\models\user.rb every
time a form is generated?

Yes, well it's not webrick doing the reloading, it is Rails, Rails
will reload all your models before each request in development mode.
Rails configuration API is found here:

http://api.rubyonrails.org/classes/Rails/Configuration.html

In particular the 'cache_classes', attribute which is configured in
the RAILS_ROOT/config/environments/*.rb filles. You can also review
the following files for descriptions of the various options:

* RAILS_ROOT/config/environment.rb
* RAILS_ROOT/config/environments/development.rb
* RAILS_ROOT/config/environments/production.rb
* RAILS_ROOT/config/environments/test.rb

Assuming it is reloading .\app\models\user.rb in development mode ...
will it do this in production mode?

'cache_classes' is set to true by default in
RAILS_ROOT/config/environments/production.rb. This disables reloading
in production mode.

Also, when you're in the rails console, you can manually reload
classes by calling 'reload!'.

The rails mailing list will be able to provide much more satisfactory
answers regarding such items in the future. You should post rails
related questions there.

 

[Ralph Shnelvar]

MH> Yes, well it's not webrick doing the reloading, it is Rails, Rails
MH> will reload all your models before each request in development mode.
MH> Rails configuration API is found here:

MH> http://api.rubyonrails.org/classes/Rails/Configuration.html

MH> In particular the 'cache_classes', attribute which is configured in
MH> the RAILS_ROOT/config/environments/*.rb filles. You can also review
MH> the following files for descriptions of the various options:

MH> * RAILS_ROOT/config/environment.rb
MH> * RAILS_ROOT/config/environments/development.rb
MH> * RAILS_ROOT/config/environments/production.rb
MH> * RAILS_ROOT/config/environments/test.rb

MH> 'cache_classes' is set to true by default in
MH> RAILS_ROOT/config/environments/production.rb. This disables reloading
MH> in production mode.

MH> Also, when you're in the rails console, you can manually reload
MH> classes by calling 'reload!'.

MH> The rails mailing list will be able to provide much more satisfactory
MH> answers regarding such items in the future. You should post rails
MH> related questions there.

The question I was trying to ask was ...

What _Ruby_ facility does Rails use to reload the class?

 

[Markus Roberts]

The question I was trying to ask was ...

What _Ruby_ facility does Rails use to reload the class?

As a rough answer, Kernel#load and the various const-introspection
methods (to remove the old class first).

The great thing about open source is that if you'd like a more
detailed answer you can just go look at the code and see for yourself.

-- Markus

 

[Ryan Davis]

What _Ruby_ facility does Rails use to reload the class?

#load will always load a file (contrasted to #require). Rails does a few =
other things during reload, but that's the main mechanism for it.