Use inheritance to obey the Open/Closed Principle

* Uses a subclass to add unsubscribeable behavior
* Demonstrates when subclasses are ugly

Author: jferris

example_app/app/models/invitation.rb

@@ -15,19 +15,13 @@ def to_param
   end
 
   def deliver
-    unless unsubscribed?
-      body = InvitationMessage.new(self).body
-      Mailer.invitation_notification(self, body).deliver
-    end
+    body = InvitationMessage.new(self).body
+    Mailer.invitation_notification(self, body).deliver
   end
 
   private
 
   def set_token
     self.token = SecureRandom.urlsafe_base64
   end
-
-  def unsubscribed?
-    Unsubscribe.where(email: recipient_email).exists?
-  end
 end

example_app/app/models/survey_inviter.rb

@@ -31,7 +31,7 @@ def deliver_invitations
   def create_invitations
     Invitation.transaction do
       recipients.map do |recipient_email|
-        Invitation.create!(
+        UnsubscribeableInvitation.create!(
           survey: survey,
           sender: sender,
           recipient_email: recipient_email,

example_app/app/models/unsubscribeable_invitation.rb

@@ -0,0 +1,13 @@
+class UnsubscribeableInvitation < Invitation
+  def deliver
+    unless unsubscribed?
+      super
+    end
+  end
+
+  private
+
+  def unsubscribed?
+    Unsubscribe.where(email: recipient_email).exists?
+  end
+end

example_app/spec/models/invitation_spec.rb

@@ -26,22 +26,8 @@
     message.should have_body_text(survey_url(invitation.survey))
   end
 
-  it 'sends nothing to users that have unsubscribed' do
-    unsubscribe = create(:unsubscribe)
-    deliver_invitation(recipient_email: unsubscribe.email)
-
-    find_email(unsubscribe.email).should be_nil
-  end
-
   def deliver_invitation(overrides = {})
-    attributes = {
-      message: 'hello',
-      survey: create(:survey)
-    }.merge(overrides)
-
-    create(:invitation, attributes).tap do |invitation|
-      invitation.deliver
-    end
+    InvitationDeliverer.new(Invitation).deliver_invitation(overrides)
   end
 end
 

example_app/spec/models/survey_inviter_spec.rb

@@ -23,7 +23,11 @@
   it "doesn't send emails if any invitations fail to save" do
     invitation = stub('invitation', deliver: true)
     error = StandardError.new('failure')
-    Invitation.stubs(:create!).returns(invitation).then.raises(error)
+    UnsubscribeableInvitation.
+      stubs(:create!).
+      returns(invitation).
+      then.
+      raises(error)
     params = valid_params(recipients: 'one@example.com,two@example.com')
     inviter = SurveyInviter.new(params)
 

example_app/spec/models/unsubscribeable_invitation_spec.rb

@@ -0,0 +1,25 @@
+require 'spec_helper'
+
+describe UnsubscribeableInvitation, '#deliver' do
+  include Rails.application.routes.url_helpers
+  self.default_url_options = ActionMailer::Base.default_url_options
+
+  it 'sends email notifications to new users' do
+    invitation = deliver_invitation
+
+    find_email(invitation.recipient_email).
+      should have_body_text(invitation.message)
+  end
+
+  it 'sends nothing to users that have unsubscribed' do
+    unsubscribe = create(:unsubscribe)
+    deliver_invitation(recipient_email: unsubscribe.email)
+
+    find_email(unsubscribe.email).should be_nil
+  end
+
+  def deliver_invitation(overrides = {})
+    InvitationDeliverer.new(UnsubscribeableInvitation).
+      deliver_invitation(overrides)
+  end
+end

example_app/spec/support/invitation_deliverer.rb

@@ -0,0 +1,19 @@
+class InvitationDeliverer
+  include FactoryGirl::Syntax::Methods
+
+  def initialize(factory)
+    @factory = factory
+  end
+
+  def deliver_invitation(overrides = {})
+    attributes = {
+      message: 'hello',
+      survey: create(:survey)
+    }.merge(overrides)
+    invitation_attributes = create(:invitation, attributes).attributes
+
+    @factory.new(invitation_attributes).tap do |invitation|
+      invitation.deliver
+    end
+  end
+end