Use the friendly ID gem for contest slugs

app/models/contest.rb

@@ -13,6 +13,7 @@
 #
 # Indexes
 #
+#  index_contests_on_slug     (slug) UNIQUE
 #  index_contests_on_user_id  (user_id)
 #
 # Foreign Keys
@@ -20,12 +21,14 @@
 #  user_id  (user_id => users.id)
 #
 class Contest < ApplicationRecord
-  belongs_to :user
+  extend FriendlyId
 
+  belongs_to :user
   has_many :completions, dependent: :destroy
   has_many :contestants, dependent: :destroy
   has_many :puzzles, dependent: :destroy
 
+  friendly_id :name, use: :slugged
+
   validates :name, presence: true
-  validates :slug, presence: true, uniqueness: true, format: { with: /\A(\w|-)*\z/, message: 'Only alphanumeric characters, "-" and "_" allowed.' }
 end