Avoid deleting categories which still have articles.

app/controllers/article_categories_controller.rb

@@ -12,6 +12,12 @@ class ArticleCategoriesController < ApplicationController
     update!(:notice => "Die Kategorie wurde aktualisiert") { article_categories_path }
   end
 
+  def destroy
+    destroy!
+  rescue => error
+    redirect_to article_categories_path, alert: t('controller.article_categories.destroy.error', message: error.message)
+  end
+
   protected
 
   def collection

app/models/article_category.rb

@@ -3,5 +3,13 @@ class ArticleCategory < ActiveRecord::Base
 
   validates :name, :presence => true, :uniqueness => true, :length => { :in => 2..20 }
 
+  before_destroy :check_for_associated_articles
+
+  protected
+
+  def check_for_associated_articles
+    raise I18n.t('activerecord.errors.has_many_left', collection: Article.model_name.human) if articles.exists?
+  end
+
 end