Migrate User to abstract class

app/models/user.rb

@@ -0,0 +1,34 @@
+class User < ApplicationRecord
+  self.abstract_class = true
+
+  ROLES = %w(admin teacher)
+
+  belongs_to :consumer
+  has_many :exercises, as: :user
+  has_many :file_types, as: :user
+  has_many :submissions, as: :user
+  has_many :participations, through: :submissions, source: :exercise, as: :user
+  has_many :user_proxy_exercise_exercises, as: :user
+  has_many :user_exercise_interventions, as: :user
+  has_many :interventions, through: :user_exercise_interventions
+  accepts_nested_attributes_for :user_proxy_exercise_exercises
+
+
+  scope :with_submissions, -> { where('id IN (SELECT user_id FROM submissions)') }
+
+  ROLES.each do |role|
+    define_method("#{role}?") { try(:role) == role }
+  end
+
+  def internal_user?
+    is_a?(InternalUser)
+  end
+
+  def external_user?
+    is_a?(ExternalUser)
+  end
+
+  def to_s
+    displayname
+  end
+end