Added validation errors to notice.

app/controllers/categories_controller.rb

@@ -4,7 +4,7 @@ class CategoriesController < ApplicationController
   # GET /categories
   # GET /categories.json
   def index
-    @categories = Category.all
+    @categories = User.find(session[:user_id]).categories
   end
 
   # GET /categories/1
@@ -30,7 +30,7 @@ class CategoriesController < ApplicationController
 
     respond_to do |format|
       if @category.save
-        format.html { redirect_to @category, notice: 'Category was successfully created.' }
+        format.html { redirect_to :categories, notice: 'Category was successfully created.' }
         format.json { render :show, status: :created, location: @category }
       else
         format.html { render :new }
@@ -56,10 +56,13 @@ class CategoriesController < ApplicationController
   # DELETE /categories/1
   # DELETE /categories/1.json
   def destroy
-    @category.destroy
-    respond_to do |format|
-      format.html { redirect_to categories_url, notice: 'Category was successfully destroyed.' }
-      format.json { head :no_content }
+    if @category.destroy
+      respond_to do |format|
+        format.html { redirect_to categories_url, notice: 'Category was successfully destroyed.' }
+        format.json { head :no_content }
+      end
+    else
+      redirect_to categories_url, notice: @category.errors.full_messages.first
     end
   end
 

app/models/category.rb

@@ -1,10 +1,12 @@
 class Category < ApplicationRecord
   has_many :documents
-  has_many :subcategories, class_name: 'Category', foreign_key: 'parent_id', dependent: :destroy
+  has_many :subcategories, class_name: 'Category', foreign_key: 'parent_id'
   belongs_to :parent, class_name: 'Category', optional: true
   belongs_to :user
 
-  before_destroy :check_for_subcategories
+  before_destroy :check_for_subcategories, :check_for_documents
+
+  validates :name, presence: true
 
   def get_fqcn
     fqcn = name
@@ -25,4 +27,11 @@ class Category < ApplicationRecord
         throw :abort
       end
     end
+
+    def check_for_documents
+      unless documents.empty?
+        errors.add(:base, 'Documents present')
+        throw :abort
+      end
+    end
 end

app/models/document.rb

@@ -4,6 +4,8 @@ class Document < ApplicationRecord
   has_one :content, dependent: :destroy, required: false
   has_and_belongs_to_many :tags
 
+  validates :category, :doc, presence: true 
+
   has_attached_file :doc,
   {
     styles: { thumb: ["200x", :png] },