Add offline model and "new" form/controller

app/models/contest.rb

@@ -31,6 +31,7 @@ class Contest < ApplicationRecord
   has_many :contestants, dependent: :destroy
   has_many :puzzles, dependent: :destroy
   has_many :messages, dependent: :destroy
+  has_many :offlines, dependent: :destroy
 
   friendly_id :name, use: :slugged
 

app/models/offline.rb

@@ -0,0 +1,27 @@
+# == Schema Information
+#
+# Table name: offlines
+#
+#  id         :integer          not null, primary key
+#  end_time   :datetime
+#  start_time :datetime         not null
+#  created_at :datetime         not null
+#  updated_at :datetime         not null
+#  contest_id :integer          not null
+#
+# Indexes
+#
+#  index_offlines_on_contest_id  (contest_id)
+#
+# Foreign Keys
+#
+#  contest_id  (contest_id => contests.id)
+#
+class Offline < ApplicationRecord
+  belongs_to :contest
+
+  has_one_attached :start_image
+  has_one_attached :end_image
+
+  validates :start_time, presence: true
+end