Rails - May 2010 - Getting class in /lib folder to see a model (const_missing)?

Hello,

I wrote a new class that I decided to put in the /app/lib folder. Part
way through one of the methods, I call #new on the model, update some of
the fields and then call #save (on the model).

When I do this though, I get a ''const_missing'' error coming
from Active
Support. Here''s the error:

"......./lib/active_support/dependencies.rb:105:in
`const_missing'':
uninitialized constant ClassA::ModelA (NameError)"

The ''ModelA'' is the model I''m trying to access, and
''ClassA'' is the
class in /app/lib/class_a.rb. I''m not sure why it seems to think that
ModelA is a part of ClassA, perhaps that''s the problem?

I would have probably just used "require ../models/model_a.rb", but I
found the following at StackOverflow:

"One way to solve this would be to explicitly require the model file
aircraft.rb. However, you will find this approach quickly leads to
insanity as it will break the Rails auto-loader in subtle and
astonishing ways. Rails is much easier if you work with the Rails class
loader, not against it."

Source:
http://stackoverflow.com/questions/326277/rails-calling-a-model-class-in-a-library

I then found an example at
http://www.strictlyuntyped.com/2008/06/rails-where-to-put-other-files.html
that suggests adding this to the file in the /app/lib folder:

  def self.included(base)
     base.extend(ClassMethods)
  end

And then creating a file in /config/initializers with the following:

  require ''rails_extensions/user_logger''

  ActionController::Base.class_eval do
    include ActionController::UserLogger
  end

Being new to Ruby/Rails, I''m really not sure what this supposed to do,
but I''m guessing it will work. That post was written in 2008 though, so
I''m thinking there may be a better way for this.

Does anyone have a suggestion as to the best way to get a class in the
/app/lib folder to see a model?

Thank you very much,
Mike
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On May 4, 2:57 am, "Mike P."
<li...-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
> I would have probably just used "require ../models/model_a.rb",
but I
> found the following at StackOverflow:
>
> "One way to solve this would be to explicitly require the model file
> aircraft.rb. However, you will find this approach quickly leads to
> insanity as it will break the Rails auto-loader in subtle and
> astonishing ways. Rails is much easier if you work with the Rails class
> loader, not against it."
That can indeed happen (the thing that breaks is usually the code
reloading in development mode).
Does the rest of your app pick up this model automatically. How/where
is this class in /lib being used ?

Fred

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Frederick Cheung wrote:
> On May 4, 2:57�am, "Mike P."
<li...-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
> 
>> I would have probably just used "require
../models/model_a.rb", but I
>> found the following at StackOverflow:
>>
>> "One way to solve this would be to explicitly require the model
file
>> aircraft.rb. However, you will find this approach quickly leads to
>> insanity as it will break the Rails auto-loader in subtle and
>> astonishing ways. Rails is much easier if you work with the Rails class
>> loader, not against it."
> 
> That can indeed happen (the thing that breaks is usually the code
> reloading in development mode).
> Does the rest of your app pick up this model automatically. How/where
> is this class in /lib being used ?
> 
> Fred
Hi Fred,

Thanks for your response. The other parts of the app (i.e. the 
controllers) do seem to pick up this model. The class in the /lib folder 
is being used separately. I''m currently running it manually, but
I''m
looking into running it automatically using  a cron job or something 
similar later on.

So, it''s not included by another file at the moment, as it''s
meant to
run as a standalone script. (I''m guessing that may have fixed the 
problem if that file already had access to the model.)

Thanks,
Mike


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On May 4, 3:35 pm, "Mike P."
<li...-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
> Thanks for your response. The other parts of the app (i.e. the
> controllers) do seem to pick up this model. The class in the /lib folder
> is being used separately. I''m currently running it manually, but
I''m
> looking into running it automatically using  a cron job or something
> similar later on.
>
> So, it''s not included by another file at the moment, as
it''s meant to
> run as a standalone script. (I''m guessing that may have fixed the
> problem if that file already had access to the model.)
What does running it manually mean - is the rails environment loaded ?
If it isn''t then you have your answer (since one of the things that
gets you is rails'' magic file loader)

Fred
>
> Thanks,
> Mike
>
> --
> Posted viahttp://www.ruby-forum.com/.
>
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On Mon, May 3, 2010 at 9:57 PM, Mike P.
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> When I do this though, I get a ''const_missing'' error
coming from Active
> Support. Here''s the error:
>
> "......./lib/active_support/dependencies.rb:105:in
`const_missing'':
> uninitialized constant ClassA::ModelA (NameError)"
>
> The ''ModelA'' is the model I''m trying to access,
and ''ClassA'' is the
> class in /app/lib/class_a.rb. I''m not sure why it seems to think
that
> ModelA is a part of ClassA, perhaps that''s the problem?
Shouldn''t it be in

{Rails.root}/lib/class_a.rb

rather than

{Rails.root}/app/lib/class_a.rb

????

-- 
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Frederick Cheung wrote:
> On May 4, 3:35�pm, "Mike P."
<li...-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
> 
>> Thanks for your response. The other parts of the app (i.e. the
>> controllers) do seem to pick up this model. The class in the /lib
folder
>> is being used separately. I''m currently running it manually,
but I''m
>> looking into running it automatically using �a cron job or something
>> similar later on.
>>
>> So, it''s not included by another file at the moment, as
it''s meant to
>> run as a standalone script. (I''m guessing that may have fixed
the
>> problem if that file already had access to the model.)
> 
> What does running it manually mean - is the rails environment loaded ?
> If it isn''t then you have your answer (since one of the things
that
> gets you is rails'' magic file loader)
> 
> Fred
Ah! That was the problem, thank you! I''ve been running it using:

$ ruby app/lib/class_a.rb

(The file has a call to "run()" outside of the class methods, which 
calls ClassA::run.)

But by running the script using the line below, the Rails environment is 
loaded properly and the script works fine. :)

$ script/runner app/lib/class_a.rb

I''m still kinda new to Rails, so I didn''t know that
I''d need to do that,
but it makes total sense!
> Shouldn''t it be in
> 
> {Rails.root}/lib/class_a.rb
> 
> rather than
> 
> {Rails.root}/app/lib/class_a.rb
> 
> ????
> 
> --
> Rick DeNatale
By ''{Rails.root}'', do you mean the app''s root
directory, or the Rails
root directory?

Anyway, I put it in {AppRoot}/app/lib because, for some reason, I 
thought that the {AppRoot}/lib folder was for external libraries (i.e. 
the ones I didn''t write). I like it this way anyway because things are 
separated better, in my opinion. I know that the stuff in the /app 
directory are the things that I made, and I don''t really need to visit 
the {AppRoot}/lib folder unless there''s something in there that I want 
to modify.

Or is this against Rails'' best practices?

Thanks again,
Mike

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