Rails - Nov 2006 - Add dynamic instance methods in a controller class

Hello All,

I have a problem while developping an application using rails.
I''d like to add some methods to my controller depending upon some
parameters read from an xml file during initialisation (I hope I am
quite clear :-) )
Below is the code I am using:

----------------
require ''rexml/Document''
include REXML

class MyController < ApplicationController

       def index
               # Xsd is a model (not ActiveRecord that is used to get
values from an XML file
               xsd = Xsd.new("myfile.xsd")

               # Get main section
               @main_sections = xsd.get_main_sections

               # Get item for first section
               @item xsd.get_items_per_section(@main_sections[0].to_s)

               # Dynamically create method for to retrieve list of
fields for each
main sections
               # THIS PART IS NOT WORKING
               @main_sections.each do |section|
                       self.instance_eval{
define_method("get_item_for_#{section}") {"toto"}}
               end
       end
end
-----------------


While testing this, I have an error message saying that the
define_method does not exist !!!!
Why is this method not found ???
I am still not sure about the instance_eval, class_eval, define_method
I need to use.
Do you have any clues regarding this problem ?

Thanks a lot,

Luc


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Hello All,

(I first tried to post this message directly from googlegroup but it
did not show up, do you know why ?)

I have a problem while developping an application using rails.
I''d like to add some methods to my controller depending upon some
parameters read from an xml file during initialisation (I hope I am
quite clear :-) )
Below is the code I am using:

----------------
require ''rexml/Document''
include REXML

class MyController < ApplicationController

        def index
                # Xsd is a model (not ActiveRecord that is used to get
values from an XML file
                xsd = Xsd.new("myfile.xsd")

                # Get main section
                @main_sections = xsd.get_main_sections

                # Get item for first section
                @item = xsd.get_items_per_section(@main_sections[0].to_s)

                # Dynamically create method for to retrieve list of
fields for each
main sections
                # THIS PART IS NOT WORKING
                @main_sections.each do |section|
                        self.instance_eval{
define_method("get_item_for_#{section}") {"toto"}}
                end
        end
end
-----------------


While testing this, I have an error message saying that the
define_method does not exist !!!!
Why is this method not found ???
I am still not sure about the instance_eval, class_eval, define_method
I need to use.
Do you have any clues regarding this problem ?

Thanks a lot,

Luc

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Hi --

On Sun, 5 Nov 2006, Luc Juggery wrote:
>
> Hello All,
>
> (I first tried to post this message directly from googlegroup but it
> did not show up, do you know why ?)
>
> I have a problem while developping an application using rails.
> I''d like to add some methods to my controller depending upon some
> parameters read from an xml file during initialisation (I hope I am
> quite clear :-) )
> Below is the code I am using:
>
> ----------------
> require ''rexml/Document''
> include REXML
>
> class MyController < ApplicationController
>
>        def index
>                # Xsd is a model (not ActiveRecord that is used to get
> values from an XML file
>                xsd = Xsd.new("myfile.xsd")
>
>                # Get main section
>                @main_sections = xsd.get_main_sections
>
>                # Get item for first section
>                @item = xsd.get_items_per_section(@main_sections[0].to_s)
>
>                # Dynamically create method for to retrieve list of
> fields for each
> main sections
>                # THIS PART IS NOT WORKING
>                @main_sections.each do |section|
>                        self.instance_eval{
instance_eval just sets "self" temporarily to a new value.  In this
case, you''re setting self to self :-)
> define_method("get_item_for_#{section}") {"toto"}}
>                end
>        end
> end
>
>
> While testing this, I have an error message saying that the
> define_method does not exist !!!!
> Why is this method not found ???
Because it''s not a method of the object to which you''re
sending the
message -- namely, your controller object.  It''s a method of the
controller *class*.  So you''d want to do:

   self.class.class_eval { define_method .... }


David

-- 
                   David A. Black |
dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org
Author of "Ruby for Rails"   [1] | Ruby/Rails training &
consultancy [3]
DABlog (DAB''s Weblog)        [2] | Co-director, Ruby Central, Inc.  
[4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org

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Great, thanks a lot David,
I will try this !!!!
Luc

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Helo David,

I tried the following code but this is not working:

@main_sections.each do |section|
	puts "defining get_item_for_#{section} method"
       	self.class.class_eval do
		puts "before defining method"
               	define_method("get_item_for_#{section}") do
			puts "inside defining method"
		end
		puts "after defining method"
	end
end

several methods should be created (get_item_for_header,
get_item_for_competencies, ...)

In the log file (in the server console), they seems to be defined:
---
defining get_item_for_header method
before defining method
after defining method
defining get_item_for_competencies method
before defining method
after defining method
...
---

bug when I try http://localhost:3000/cv/get_item_for_header I got the
following error:

Unknown action
No action responded to get_item_for_header

if I open a console and list all the CvController methods, the new
methods do not show up.

Do you have any idea?

Thanks a lot,

Luc


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Hello All,

Does everybody have a clue for this problem?
I guess this is more ruby related but as a controller is in the
place... :-)

Thanks a lot,

Luc

Luc wrote:
> Helo David,
>
> I tried the following code but this is not working:
>
> @main_sections.each do |section|
> 	puts "defining get_item_for_#{section} method"
>        	self.class.class_eval do
> 		puts "before defining method"
>                	define_method("get_item_for_#{section}") do
> 			puts "inside defining method"
> 		end
> 		puts "after defining method"
> 	end
> end
>
> several methods should be created (get_item_for_header,
> get_item_for_competencies, ...)
>
> In the log file (in the server console), they seems to be defined:
> ---
> defining get_item_for_header method
> before defining method
> after defining method
> defining get_item_for_competencies method
> before defining method
> after defining method
> ...
> ---
>
> bug when I try http://localhost:3000/cv/get_item_for_header I got the
> following error:
>
> Unknown action
> No action responded to get_item_for_header
>
> if I open a console and list all the CvController methods, the new
> methods do not show up.
> 
> Do you have any idea?
> 
> Thanks a lot,
> 
> Luc

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Hi --

On Sun, 5 Nov 2006, Luc wrote:
>
> Helo David,
>
> I tried the following code but this is not working:
>
> @main_sections.each do |section|
> 	puts "defining get_item_for_#{section} method"
>       	self.class.class_eval do
> 		puts "before defining method"
>               	define_method("get_item_for_#{section}") do
> 			puts "inside defining method"
> 		end
> 		puts "after defining method"
> 	end
> end
>
> several methods should be created (get_item_for_header,
> get_item_for_competencies, ...)
Is this at the top level of the class (rather than in an instance
method)?  If so, lose the "self.class." part :-)


David

-- 
                   David A. Black |
dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org
Author of "Ruby for Rails"   [1] | Ruby/Rails training &
consultancy [3]
DABlog (DAB''s Weblog)        [2] | Co-director, Ruby Central, Inc.  
[4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org

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Hi again --

On Sun, 5 Nov 2006, Luc wrote:
> In the log file (in the server console), they seems to be defined:
> ---
> defining get_item_for_header method
> before defining method
> after defining method
> defining get_item_for_competencies method
> before defining method
> after defining method
> ...
> ---
>
> bug when I try http://localhost:3000/cv/get_item_for_header I got the
> following error:
>
> Unknown action
> No action responded to get_item_for_header
I think I (finally) spot the issue.  The new methods are not going to
persist from one action to another.  You might need to define them in
a before_filter, so that they''ll get defined each time, or find some
other way to persist or cache them.


David

-- 
                   David A. Black |
dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org
Author of "Ruby for Rails"   [1] | Ruby/Rails training &
consultancy [3]
DABlog (DAB''s Weblog)        [2] | Co-director, Ruby Central, Inc.  
[4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org

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Hi David,

So you think the class definition is not keep from one action to the
other one? Then the problem I have make some sense. But, isn''t strange
to have to redefine those methods each time ? I think I will then need
to find a way to store the sections array to be able to reconstruct the
methd for each action.
What is the best way to keep variable to one action to another, can I
use a session variable ?

Thanks a lot David (those problem are good for me as I can learn rails
then :-) )
Cheers,
Luc


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Hello David,

I got your point and set a before_filter in which I create those
methods, that seems to work fine that way.
But, because there is a but :-), I do not really understand why after
having added some instance method to a given class, those methods are
not available to all instances created afterwards !!!! This seems
really strange and that make me think that maybe I am not using the
correct syntax to define my methods within the index method !!!!
What do you think ?

Sorry for bothering you with this,

Thanks a lot,

Luc


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