Duplicating Rails model for a form with meta-programming

Question

Can someone please review my code:

# dup/ish -> //github.com/rails/rails/issues/5449
class Form
 include Mongoid::Document
 attr_accessor :source
 def self.ish(prefix, suffix, &block)
 klass_name = prefix.classify + suffix
 dup.tap do |klass|
 klass.class_eval do
 define_singleton_method(:name) do
 prefix.classify
 end
 end
 klass.class_eval(&block)
 Object.const_set(klass_name, klass)
 end
 end
 def self.compose(klass_name, id, source)
 mongoid_translate = {:models => {}, :attributes => {}}
 form = ish(klass_name, id) do
 translate = {}
 source.flatten.each do |widget|
 if widget.include?('validate')
 validates *widget.values_at('name', 'validate')
 translate.store *widget.values_at('name', 'translate')
 end
 if widget.include?('name')
 if 'upload' == widget['type']
 has_many(:attachments)
 accepts_nested_attributes_for(:attachments)
 elsif 'repeat' == widget['type']
 part_klass = Form.compose(widget['name'], id, widget['parts'])
 embeds_many(widget['name'].pluralize, :class_name => part_klass.class.to_s)
 accepts_nested_attributes_for(widget['name'].pluralize)
 end
 end
 end
 mongoid_translate[:attributes][self.name.downcase.to_sym] = translate
 end
 I18n.backend.store_translations(:pt_BR, {:mongoid => mongoid_translate})
 form.new.tap do |form|
 form.source = source
 end
 end
 def prepare
 self.source.flatten.each do |widget|
 if widget.include?('name')
 if 'repeat' == widget['type']
 parts = send("#{widget['name'].pluralize}")
 if parts.empty?
 parts.build
 widget['parts'].each do |part|
 parts[0].write_attribute(part['name'], nil)
 end
 end
 elsif 'upload' == widget['type']
 attachments.build if attachments.empty?
 else
 begin
 send(widget['name'].to_sym)
 rescue NoMethodError
 write_attribute(widget['name'], nil)
 end
 end
 end
 end
 end
end

Answer 1

Few things I have noted in your design are listed below. Beware all of this is purely from a design perspective rather than application.

1. Source is defined as attr_accessor which essentially violates encapsulation. Inject it from outside in constructor call.(I am not able to understand why you have not gone for attr_reader instead of accessor.
2. Ideally self.compose can be split into different method calls. It is violating SRP by doing too many things at one place. That is same for other methods as well.
3. Speaking from a puritan view, the branched if condition is also a smell.

In general, metaprogramming is considered to be something which must be avoided unless you have enough justification to keep it.

• Arthur Corenzan: Whoa I totally forgot I put this here. :P And yes I see very well all your points. It's actually something I knew had smells all over the place but wanted to check with other people (which I couldn't because I was the only programmer working on the project). Thanks for your time and effort! Have a great day.
• Anony-mouse: my pleasure! there might be more smells.