Question

I’m using ActiveModel in one of my projects and I wanted to ask what is the best way for dynamic methods defining in next situation

Base ActiveModel class has only 1 accessor attribute called attributes.

  def initialize(attributes = {})
      set_default_attributes!
      @attributes.merge!(attributes.symbolize_keys)
      @new_record = true    
   end

   def read_attribute_for_validation(key)
      @attributes[key]
   end


   def self.create(attributes={})
     obj = self.new(attributes)
     obj.save
     return obj
   end

   def save
     if self.valid?
       puts "saved!"
       return true
     end   
     return false
  end    


  def update_attributes(attributes={})
     self.attributes.merge!(attributes.symbolize_keys)
     self.save
  end     



  def as_json(options={})
      hash = Hash.new
      hash.merge!(self.attributes)
      hash.as_json({:root=>false}.merge!(options || {}))

  end  

methods should be like accessors but should use internal @attributes variable

Example if @attributes is hash like {:param1=>1,:param2=>2}

instance object should have next methods

param1
param1=
param2
param2=

I tried to use method missing but if method finished with “=” I need to parse it and check attributes for such key so I don’t like how code looks like.

Answer 1

you can add methods with singleton_class.module_eval

def initialize(attributes = {})
   set_default_attributes!
   @attributes.each do |key,value|
     singleton_class.module_eval do
       define_method(key) { self.attributes[key] } unless method_defined? key
       define_method("#{key}=") { |new_value|  self.attributes[key] = new_value } unless method_defined? "#{key}="
     end
   end
   @attributes.merge!(attributes.symbolize_keys)
   @new_record = true

 end