event categoriy is required

app/assets/javascripts/controllers/admin/events.coffee

@@ -228,6 +228,7 @@ Application.Controllers.controller "NewEventController", ["$scope", "$state", "$
     end_time: new Date()
     all_day: 'false'
     recurrence: 'none'
+    category_ids: []
 
   ## Possible types of recurrences for an event
   $scope.recurrenceTypes = [

app/assets/templates/events/_form.html.erb

@@ -69,7 +69,7 @@
 
     </div>   <!-- ./panel-body  -->
     <div class="panel-footer no-padder">
-      <input type="submit" ng-value="submitName" class="r-b btn-valid btn btn-warning btn-block p-lg btn-lg text-u-c" ng-disabled="eventForm.$invalid"/>
+      <input type="submit" ng-value="submitName" class="r-b btn-valid btn btn-warning btn-block p-lg btn-lg text-u-c" ng-disabled="eventForm.$invalid || event.category_ids.length === 0"/>
     </div>
     </section>
 

app/models/event.rb

@@ -6,6 +6,7 @@ class Event < ActiveRecord::Base
   has_many :event_files, as: :viewable, dependent: :destroy
   accepts_nested_attributes_for :event_files, allow_destroy: true, reject_if: :all_blank
   has_and_belongs_to_many :categories, join_table: :events_categories
+  validates :categories, presence: true
 
   belongs_to :availability, dependent: :destroy
   accepts_nested_attributes_for :availability