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How can I do this without eval...

J2M

9/1/2006 11:14:00 PM

def load_default_attributes(model_name, options = {})
fixture = options[:fixture] || :default
attributes = temp_attributes = model = {}
instance_eval <<-FIN
temp_attributes = #{model_name.to_s.pluralize}("#{fixture}")
model = #{model_name.to_s.capitalize}
FIN
.
.
.
end

I know there must be a neater way to get hold of a class (or in this
case a Rails model) and with the temp_attributes to get hold of a
fixture, can anybody shed some metaprogramming light?

Thanks.
5 Answers

e

9/1/2006 11:30:00 PM

0

James Mccarthy wrote:
> def load_default_attributes(model_name, options = {})
> fixture = options[:fixture] || :default
> attributes = temp_attributes = model = {}
> instance_eval <<-FIN
> temp_attributes = #{model_name.to_s.pluralize}("#{fixture}")

send model_name.to_s.pluralize, fixture

> model = #{model_name.to_s.capitalize}

self.class.const_get model_name.to_s.capitalize

> FIN
> .
> .
> .
> end
>
> I know there must be a neater way to get hold of a class (or in this
> case a Rails model) and with the temp_attributes to get hold of a
> fixture, can anybody shed some metaprogramming light?

The above should work in principle; however, take a
look at ri Object#send and Module#const_get in case
you run into any problems.

(Disclaimer: respondent is not proficient with Rails.)

> Thanks.


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

Jano Svitok

9/1/2006 11:43:00 PM

0

On 9/2/06, J2M <james2mccarthy@gmail.com> wrote:
> def load_default_attributes(model_name, options = {})
> fixture = options[:fixture] || :default
> attributes = temp_attributes = model = {}
> instance_eval <<-FIN
> temp_attributes = #{model_name.to_s.pluralize}("#{fixture}")
> model = #{model_name.to_s.capitalize}
> FIN

Hi,

model = const_get(model_name.to_s.capitalize)

Classes are constants. So you can get them by name (string or symbol)
with Module#const_get

temp_attributes... I don't know what fixtures are, I'll just say that you can
- call a method with Object#send(name, arg1, arg2) or send(name, *args)
- get/set instance variable with
instance_variable_get/instance_variable_set (don't forget the @!
my_object.instance_variable_get('@name') )
- class variables with Module#class_variable_get/.._set

and generally, look into Module, Class, Object and Kernel for other
useful methods ;-)

finally http://www.rubycentral.com/book/o... can be helpful.

J2M

9/2/2006 1:35:00 AM

0


Jan Svitok wrote:

> model = const_get(model_name.to_s.capitalize)

Excellent, thank you.

Paul Duncan

9/2/2006 8:19:00 PM

0

* J2M (james2mccarthy@gmail.com) wrote:
>
> Jan Svitok wrote:
>
> > model = const_get(model_name.to_s.capitalize)

This might be more appropriate:

model_class = const_get(model_name.to_s.classify)

Classify will take care of things that capitalize misses, like
underscores and extraneous plurals. Take a look at the following
output:

# test strings and test methods
strings = %w{blog_post layers magazine_subscribers}
methods = %w{capitalize classify}.map { |m| m.intern }

# iterate over test strings and handle each one
puts strings.map { |str|
"'#{str}'\n" << methods.map { |meth|
" #{meth}:\t'#{str.send(meth)}'"
}.join("\n")
}

Produces the following:

'blog_post'
capitalize: 'Blog_post'
classify: 'BlogPost'
'layers'
capitalize: 'Layers'
classify: 'Layer'
'magazine_subscribers'
capitalize: 'Magazine_subscribers'
classify: 'MagazineSubscriber'

Hope that helps...

--
Paul Duncan <pabs@pablotron.org> pabs in #ruby-lang (OPN IRC)
http://www.pabl... OpenPGP Key ID: 0x82C29562

Ezra Zygmuntowicz

9/2/2006 8:46:00 PM

0


On Sep 2, 2006, at 1:19 PM, Paul Duncan wrote:

> * J2M (james2mccarthy@gmail.com) wrote:
>>
>> Jan Svitok wrote:
>>
>>> model = const_get(model_name.to_s.capitalize)
>
> This might be more appropriate:
>
> model_class = const_get(model_name.to_s.classify)

Also if you are already within rails you may as well use #constantize

model_class = model_name.to_s.classify.constantize

-Ezra

>
> Classify will take care of things that capitalize misses, like
> underscores and extraneous plurals. Take a look at the following
> output:
>
> # test strings and test methods
> strings = %w{blog_post layers magazine_subscribers}
> methods = %w{capitalize classify}.map { |m| m.intern }
>
> # iterate over test strings and handle each one
> puts strings.map { |str|
> "'#{str}'\n" << methods.map { |meth|
> " #{meth}:\t'#{str.send(meth)}'"
> }.join("\n")
> }
>
> Produces the following:
>
> 'blog_post'
> capitalize: 'Blog_post'
> classify: 'BlogPost'
> 'layers'
> capitalize: 'Layers'
> classify: 'Layer'
> 'magazine_subscribers'
> capitalize: 'Magazine_subscribers'
> classify: 'MagazineSubscriber'
>
> Hope that helps...
>
> --
> Paul Duncan <pabs@pablotron.org> pabs in #ruby-lang (OPN IRC)
> http://www.pabl... OpenPGP Key ID: 0x82C29562