Inject Validations

activemodel/lib/active_model/inject_validations.rb

@@ -0,0 +1,69 @@
+module ActiveModel
+  # When you have a module
+  #   
+  #   module Foo
+  #     extend ActiveModel::InjectValidations
+  #
+  #     inject_validations do |c|
+  #       c.validates_presence_of :price
+  #     end
+  #   end
+  #
+  # and a model
+  #
+  #   class Offer < ActiveRecord::Base ; end
+  #
+  # and you extend an instance of +Offer+ like this
+  #
+  #   offer = Offer.new
+  #   offer.extend(Foo)
+  #
+  # The validation behaviour of +offer+, and only that instance,
+  # will be the same as if you had
+  #
+  #   class Offer < ActiveRecord::base
+  #     validates_presence_of :price
+  #   end
+  #
+  # It assumes that all validation is done with the valid? method on the object,
+  # which is the case for the current version of ActiveModel (3.2.3).
+  module InjectValidations
+
+    def inject_validations(&block)
+      @validations = block
+    end
+
+    private
+
+    def self.extended(base)
+      base.module_eval do
+        def self.extended(real_base)
+          super(real_base)
+          context_sym = (self.name.gsub(":","").to_s + "Context").underscore.to_sym
+
+          # Do not redefine validations on base class, if already included once.
+          sym = ("@@" + context_sym.to_s).to_sym
+          unless real_base.class.class_variable_defined?(sym)
+            real_base.class.class_variable_set(sym, true)
+            vs = @validations
+            real_base.class.instance_eval do
+              with_options :on => context_sym, &vs
+            end
+          end
+
+          real_base.define_singleton_method(:valid?) do |context=nil|
+            valid = super(context_sym)
+            unless context.nil?
+              _errors = errors.to_hash
+              valid &= super(context)
+
+              # Merge errors from both contexts
+              _errors.each { |k,v| errors.set(k, (_errors[k] + v).uniq) }
+            end
+            valid
+          end
+        end
+      end
+    end
+  end
+end