Use the friendly ID gem for contest slugs

app/controllers/contests_controller.rb

@@ -84,6 +84,6 @@ class ContestsController < ApplicationController
   end
 
   def contest_params
-    params.expect(contest: [ :name, :team, :allow_registration, :slug ])
+    params.expect(contest: [ :name, :team, :allow_registration ])
   end
 end

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

app/views/contests/_form.html.slim

@@ -4,12 +4,6 @@
       .form-floating
         = form.text_field :name, autocomplete: "off", class: "form-control"
         = form.label :name, class: "required"
-  .row.mb-3
-    .col
-      .form-floating
-        = form.text_field :slug, autocomplete: "off", class: "form-control"
-        = form.label :slug, class: "required"
-      .form-text This will be used for building the public scoreboard URL: https://puzzle-scoreboard.org/public/<slug>.
   .row.mb-3
     .col
       .form-check.form-switch