Rails - Nov 2013 - add class variable to all models using concern to extend AR?

Hi All,

I''ve previously used concerns to extend my models without problems. 
I''m
now trying to extend all my models in one swell-foop by extending AR
with a concern. In brief, I want to add a class variable to each
individual model using a concern that extends AR.   Specifically - I
need to find the where (and how) to define a class variable scoped to a
specific model in my AR extending concern. Is this sane?  Possible?

Thanks,

Matt

-- 
Posted via http://www.ruby-forum.com/.

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To view this discussion on the web visit
https://groups.google.com/d/msgid/rubyonrails-talk/7142832fd8a1f54f445b9bcaa0e22ae4%40ruby-forum.com.
For more options, visit https://groups.google.com/groups/opt_out.

On Nov 20, 2013, at 9:34 AM, Matt Yoder
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
> Hi All,
> 
> I''ve previously used concerns to extend my models without
problems.  I''m
> now trying to extend all my models in one swell-foop by extending AR
> with a concern. In brief, I want to add a class variable to each
> individual model using a concern that extends AR.   Specifically - I
> need to find the where (and how) to define a class variable scoped to a
> specific model in my AR extending concern. Is this sane?  Possible?
> 
> Thanks,
> 
> Matt
> 
> — 
Maybe? This seems like requiring the children to know a specific implementation
detail of a parent class via the concern mixin. Instead, I’d provide accessor
methods.

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To view this discussion on the web visit
https://groups.google.com/d/msgid/rubyonrails-talk/54E853DE-5F8D-492F-9D9A-9041393128D4%40gmail.com.
For more options, visit https://groups.google.com/groups/opt_out.

On Wednesday, 20 November 2013 12:34:37 UTC-5, Ruby-Forum.com User
wrote:
>
> Hi All, 
>
> I''ve previously used concerns to extend my models without
problems.  I''m
> now trying to extend all my models in one swell-foop by extending AR 
> with a concern. In brief, I want to add a class variable to each 
> individual model using a concern that extends AR.   Specifically - I 
> need to find the where (and how) to define a class variable scoped to a 
> specific model in my AR extending concern. Is this sane?  Possible? 
>
>
You don''t want a class variable for this - they are shared between all
the
subclasses. A sample IRB trace:

irb: class Foo
>>     end
===> nil
irb: module Bar
>>     def wat=(value)
>>       @@wat = value
>>     end
>>
>>     def wat
>>       @@wat
>>       end
>>   end
===> nil
irb: Foo.send(:include, Bar)
===> Foo
irb: f = Foo.new
===> #<Foo:0x00000100b5a008>
irb: f.wat = ''huh''
===> "huh"
irb: f.wat
===> "huh"
irb: class Baz < Foo
>>     end
===> nil
irb: class Baz2 < Foo
>>     end
===> nil
irb: b = Baz.new
===> #<Baz:0x00000100b7ac68>
irb: b.wat
===> "huh"
irb: b2 = Baz2.new
===> #<Baz2:0x00000100b82580>
irb: b2.wat = ''nope''
===> "nope"
irb: f.wat
===> "nope" 

You likely want a class instance variable instead, to avoid the sharing. 
More details here:

http://www.railstips.org/blog/archives/2006/11/18/class-and-instance-variables-in-ruby/

--Matt Jones

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To view this discussion on the web visit
https://groups.google.com/d/msgid/rubyonrails-talk/e451922c-9f53-4aeb-802f-e5dadcb2676b%40googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.

Thanks Matt,

Your observations are exactly what I was running into.  Good to know I
should focus on class instance variables.  Inheritance is a bit of mixed
bag- I want it for all subclasses of my models whose superclass is not
AR::Base.

The link is very helpful, wish I would have seen it earlier.  A couple
followups- can you comment on whether some of the approach therein has
been replaced with the use of ''class_attribute''?  Also, do you
forsee
any issues with using a Concern rather than the extend approach
described there?

At present I''ve fallen back to just extending individual models (this
in
retrospect might be safer in the long run, albeit not as magikal).

Thanks again for your help,
Matt

-- 
Posted via http://www.ruby-forum.com/.

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To view this discussion on the web visit
https://groups.google.com/d/msgid/rubyonrails-talk/b9cd7c2110a1acb6fd2b3739834f14d2%40ruby-forum.com.
For more options, visit https://groups.google.com/groups/opt_out.