Rails - Oct 2009 - How to DRY up these methods?

I''ve clearly go a lot of repetition in the following methods:

  def name=(value)
    write_attribute(:name, if [0,"0","","
"].include? value then nil
else value end)
  end
  def address=(value)
    write_attribute(:address, if [0,"0","","
"].include? value then nil
else value end)
  end
  def city=(value)
    write_attribute(:city, if [0,"0","","
"].include? value then nil
else value end)
  end

Can someone tell me the convention to DRY this code?  I''m wondering if
I
use a lambda but am not quite sure that''s the right path or how to do
that.

Thanks,
Bill
-- 
Posted via http://www.ruby-forum.com/.

Hi --

On Sat, 17 Oct 2009, Bill Devaul wrote:
>
> I''ve clearly go a lot of repetition in the following methods:
>
>  def name=(value)
>    write_attribute(:name, if [0,"0","","
"].include? value then nil
> else value end)
>  end
>  def address=(value)
>    write_attribute(:address, if [0,"0","","
"].include? value then nil
> else value end)
>  end
>  def city=(value)
>    write_attribute(:city, if [0,"0","","
"].include? value then nil
> else value end)
>  end
>
> Can someone tell me the convention to DRY this code?  I''m
wondering if I
> use a lambda but am not quite sure that''s the right path or how to
do
> that.
One idea is simply to parameterize the process:

   def generic_writer(attr, value)
     @blanks ||= [0, "0", "", " "]
     write_attribute(attr, @blanks.include?(value) ? nil : value)
   end

   def name=(value)
     generic_writer(:name, value)
   end

etc.

If you want, you can automate the creation of the methods instead:

   %w{ name address city }.each do |attr|
     define_method("#{attr}=") do |value|
       @blanks ||= [0, "0", "", " "]
       write_attribute(attr, @blanks.include?(value) ? nil : value)
     end
   end


David

-- 
The          Ruby training with D. Black, G. Brown, J.McAnally
Compleat     Jan 22-23, 2010, Tampa, FL
Rubyist      http://www.thecompleatrubyist.com

David A. Black/Ruby Power and Light, LLC (http://www.rubypal.com)

Thanks for the help.  I used the latter to come up with:

  @fields_to_normalize = %w{ address city country_id email_general fax 
name phone phone_local state_id vacation_end_on vacation_notice 
vacation_start_on zip_code }

  @fields_to_normalize.each do |attr|
    define_method("#{attr}=") do |value|
      @blanks ||= [0, "0", "", " "]
      write_attribute(attr, @blanks.include?(value) ? nil : value)
    end
  end

Is it possible to do something more Rails-ish so it reads:

normalize_fields :address, :city, :country_id

This additional re-factoring would allow re-use across models.

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

Hi --

On Sat, 17 Oct 2009, Bill Devaul wrote:
>
> Thanks for the help.  I used the latter to come up with:
>
>  @fields_to_normalize = %w{ address city country_id email_general fax
> name phone phone_local state_id vacation_end_on vacation_notice
> vacation_start_on zip_code }
>
>  @fields_to_normalize.each do |attr|
>    define_method("#{attr}=") do |value|
>      @blanks ||= [0, "0", "", " "]
>      write_attribute(attr, @blanks.include?(value) ? nil : value)
>    end
>  end
>
> Is it possible to do something more Rails-ish so it reads:
>
> normalize_fields :address, :city, :country_id
Sure -- just write the method :-) I would consider putting the blanks
in a constant.

   class Whatever

     BLANKS = [0, "0", "", " "]

     def self.normalize_fields(*syms)
       syms.each do |attr|
         define_method("#{attr}=") do |value|
           write_attribute(attr, BLANKS.include?(value) ? nil : value)
         end
       end
     end

     normalize_fields :address, :city, :country_id
   end


David

-- 
The          Ruby training with D. Black, G. Brown, J.McAnally
Compleat     Jan 22-23, 2010, Tampa, FL
Rubyist      http://www.thecompleatrubyist.com

David A. Black/Ruby Power and Light, LLC (http://www.rubypal.com)

Thanks to your help David I now have:

# lib/normalizer.rb
module Normalizer

  BLANKS = [0, "0", "", " "]

  def self.included(base)
    base.class_eval do
      def self.normalize(*syms)
        syms.each do |attr|
          define_method("#{attr}=") do |value|
            write_attribute(attr, BLANKS.include?(value) ? nil : value)
          end
        end
      end
    end
  end

end

(I struggled with the above until I read that class_eval is needed to 
make the inclusion happen.  I wonder if a change to class_eval to yield 
the included module would feel more natural.)

and

# models/model.rb
include Normalizer
normalize :name, :address, :city, :country_id

Looks great and tests pass!

Thanks,
Bill
-- 
Posted via http://www.ruby-forum.com/.

Hi --

On Sun, 18 Oct 2009, Bill Devaul wrote:
>
> Thanks to your help David I now have:
>
> # lib/normalizer.rb
> module Normalizer
>
>  BLANKS = [0, "0", "", " "]
>
>  def self.included(base)
>    base.class_eval do
>      def self.normalize(*syms)
>        syms.each do |attr|
>          define_method("#{attr}=") do |value|
>            write_attribute(attr, BLANKS.include?(value) ? nil : value)
>          end
>        end
>      end
>    end
>  end
>
  end
>
> (I struggled with the above until I read that class_eval is needed to
> make the inclusion happen.  I wonder if a change to class_eval to yield
> the included module would feel more natural.)
You should be able to do:

   def self.included(base)
     def base.normalize(*syms)
       ...
     end
   end

I might be inclined to do:

   module Normalizer
     def normalize(*syms)
       ...
     end
   end

   class Whatever
     extend Normalizer
     ...
   end

i.e., extend the class object directly rather than grabbing it
indirectly and operating on it. It seems a little more streamlined.


David

-- 
The          Ruby training with D. Black, G. Brown, J.McAnally
Compleat     Jan 22-23, 2010, Tampa, FL
Rubyist      http://www.thecompleatrubyist.com

David A. Black/Ruby Power and Light, LLC (http://www.rubypal.com)

The second option works great as suggested.  I tip my cap to you.

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