Introduce CommonInstructionModel

1. These models are linked to one event
2. There is a user through event

app/models/concerns/common_instruction_model.rb

@@ -0,0 +1,15 @@
+module CommonInstructionModel
+  extend ActiveSupport::Concern
+
+  included do
+    belongs_to :authorization_request
+
+    has_one :event,
+      class_name: 'AuthorizationRequestEvent',
+      inverse_of: :entity,
+      dependent: :destroy
+
+    has_one :user,
+      through: :event
+  end
+end

app/models/denial_of_authorization.rb

@@ -1,9 +1,5 @@
 class DenialOfAuthorization < ApplicationRecord
-  validates :reason, presence: true
-  belongs_to :authorization_request
+  include CommonInstructionModel
 
-  has_many :events,
-    class_name: 'AuthorizationRequestEvent',
-    inverse_of: :entity,
-    dependent: :destroy
+  validates :reason, presence: true
 end

app/models/instructor_modification_request.rb

@@ -1,9 +1,5 @@
 class InstructorModificationRequest < ApplicationRecord
-  validates :reason, presence: true
-  belongs_to :authorization_request
+  include CommonInstructionModel
 
-  has_many :events,
-    class_name: 'AuthorizationRequestEvent',
-    inverse_of: :entity,
-    dependent: :destroy
+  validates :reason, presence: true
 end

app/models/revocation_of_authorization.rb

@@ -1,3 +1,3 @@
 class RevocationOfAuthorization < ApplicationRecord
-  belongs_to :authorization_request
+  include CommonInstructionModel
 end