Use ApplicationRecord

app/models/application_record.rb

@@ -0,0 +1,3 @@
+class ApplicationRecord < ActiveRecord::Base
+  self.abstract_class = true
+end

app/models/contact.rb

@@ -1,4 +1,4 @@
-class Contact < ActiveRecord::Base
+class Contact < ApplicationRecord
   has_many :phones
   accepts_nested_attributes_for :phones
 

app/models/news_release.rb

@@ -1,4 +1,4 @@
-class NewsRelease < ActiveRecord::Base
+class NewsRelease < ApplicationRecord
   validates :released_on, presence: true
   validates :title, presence: true
   validates :body, presence: true

app/models/phone.rb

@@ -1,4 +1,4 @@
-class Phone < ActiveRecord::Base
+class Phone < ApplicationRecord
   belongs_to :contact
 
   validates :phone, uniqueness: { scope: :contact_id }

app/models/user.rb

@@ -1,4 +1,4 @@
-class User < ActiveRecord::Base
+class User < ApplicationRecord
   has_secure_password
 
   validates :email, presence: true, uniqueness: true