having helpers refer to the object theyre called on

Rails 3.0.2
Ruby 1.9.3

Im currently trying to have a view's instance variable respond to the
call 'holiday?' with a boolean. i cant put it in a model's class
definition, since i use several classes that contain dates.
it works if I add the following definition to environment.rb:

class String
  def holiday? # on timestamp as string
    if Holiday.where(date: Date.parse(self)).any?
      true
    else
      false
    end
  end
end

now i can do this in my view:
<% if raw.timestamp.holiday? %>

thats nice and all, but its really seems to be the wrong way to do this,
not least because i have to restart the rails server to see changes to
the method. i tried it with the following definition, but it didnt work:

module ApplicationHelper
  def holiday? # on timestamp as string
    if Holiday.where(date: Date.parse(self)).any?
      true
    else
      false
    end
  end
end

(i also tried it with self.holiday?)

Does anyone have a tip on how to go about this?

Rails 3.0.2
Ruby 1.9.3

Im currently trying to have a view's instance variable respond to the
call 'holiday?' with a boolean. i cant put it in a model's class
definition, since i use several classes that contain dates.
it works if I add the following definition to environment.rb:

class String
def holiday? # on timestamp as string
   if Holiday.where(date: Date.parse(self)).any?
     true
   else
     false
   end
end
end

now i can do this in my view:
<% if raw.timestamp.holiday? %>

thats nice and all, but its really seems to be the wrong way to do this,
not least because i have to restart the rails server to see changes to
the method. i tried it with the following definition, but it didnt work:

module ApplicationHelper
def holiday? # on timestamp as string
   if Holiday.where(date: Date.parse(self)).any?
     true
   else
     false
   end
end
end

(i also tried it with self.holiday?)

Does anyone have a tip on how to go about this?

Adding an instance method like this is pretty much reserved for the model (or as you have noted, a monkey-patch on String). If you pass a variable into the helper, then you can do it, and the syntax isn't too much different -- it's a matter of something.holiday? vs holiday?( something.attribute ). While I agree the former is nicer, it does bind you into using the model as the source of this.

If you need to add it to more than one model, you could package it in a Concern, and then you could just include that in a number of different models, and be able to call the method there.

Walter