How can I dynamically declare these instance methods?

Question

I had to implement these methods on an ActiveRecord model in order to support some desired view functionality.

I'm thinking there has to be a more compact way to declare these methods, probably involving an Array of symbols and an Array#each call.

Any suggestions?

(These are legacy column names, BTW.)

class Contract < ActiveRecord::Base

  def start_date_displayed
    self.start_date.present? ? self.start_date.strftime("%-m/%-d/%Y") : ''
  end

  def start_date_displayed=(input)
    if input.present?
      self.start_date = Date.strptime input, '%m/%d/%Y'
    end
  end

  def end_date_displayed
    self.end_date.present? ? self.end_date.strftime("%-m/%-d/%Y") : ''
  end

  def end_date_displayed=(input)
    if input.present?
      self.end_date = Date.strptime input, '%m/%d/%Y'
    end
  end

  def ArrivalDate_displayed
    self.ArrivalDate.present? ? self.ArrivalDate.strftime("%-m/%-d/%Y") : ''
  end

  def ArrivalDate_displayed=(input)
    if input.present?
      self.ArrivalDate = Date.strptime input, '%m/%d/%Y'
    end
  end

  def Contract_ReceivedDate_displayed
    self.Contract_ReceivedDate.present? ? self.Contract_ReceivedDate.strftime("%-m/%-d/%Y") : ''
  end

  def Contract_ReceivedDate_displayed=(input)
    if input.present?
      self.Contract_ReceivedDate = Date.strptime input, '%m/%d/%Y'
    end
  end

  def Contract_FinalizedDate_displayed
    self.Contract_FinalizedDate.present? ? self.Contract_FinalizedDate.strftime("%-m/%-d/%Y") : ''
  end

  def Contract_FinalizedDate_displayed=(input)
    if input.present?
      self.Contract_FinalizedDate = Date.strptime input, '%m/%d/%Y'
    end
  end

  def Committee_Date_displayed
    self.Committee_Date.present? ? self.Committee_Date.strftime("%-m/%-d/%Y") : ''
  end

  def Committee_Date_displayed=(input)
    if input.present?
      self.Committee_Date = Date.strptime input, '%m/%d/%Y'
    end
  end

  # ...

end

Yossi & xzgyb Thanks. I wish I could accept both answers. I went with Yossi because it's the one I actually implemented. — Ethan
– Ethan, Commented May 3, 2012 at 17:11

xzgyb · Accepted Answer · 2012-05-03 05:48:11Z

class Contract < ActiveRecord::Base

  %w(start_date end_date).each do |attr_name|
     class_eval <<-METHOD_DEF
         def #{attr_name}_displayed
             self.#{attr_name}.present? ? self.#{attr_name}.strftime("%-m/%-d/%Y") : ''
         end

         def #{attr_name)_displayed=(input)
            if input.present?
              self.#{attr_name} = Date.strptime #{attr_name}, '%m/%d/%Y'
            end
         end


     METHOD_DEF
  end
end

If only define these methods for those columns that name ends with date, then

class Contract < ActiveRecord::Base

   self.column_names.grep(/date$/i).each do |column_name|

     class_eval <<-METHOD_DEF
         def #{column_name}_displayed
             self.#{column_name}.present? ? self.#{column_name}.strftime("%-m/%-d/%Y") : ''
         end

         def #{column_name)_displayed=(input)
            if input.present?
              self.#{column_name} = Date.strptime #{column_name}, '%m/%d/%Y'
            end
         end             
     METHOD_DEF

  end
end

Yossi · Accepted Answer · 2012-05-03 06:42:56Z

1

It's better to avoid plain evals when possible.

class Contract < ActiveRecord::Base
  class << self
    def attr_displayed *attrs
      attrs.each do |attr|
        displayed = :"#{attr}_displayed"

        define_method displayed do
          send(attr).present? ? send(attr).strftime("%-m/%-d/%Y") : ''
        end

        define_method :"#{displayed}=" do |input|
          if input.present?
            send :"#{attr}=", Date.strptime(input, '%m/%d/%Y')
          end
        end
      end
    end
  end

  attr_displayed :start_date, :end_date, :ArrivalDate, :Committee_Date,
                 :Contract_ReceivedDate, :Contract_FinalizedDate
end

answered May 3, 2012 at 6:42

Yossi

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