diff --git a/app/controllers/projects_controller.rb b/app/controllers/projects_controller.rb
index 3428bd0..bf460f0 100644
--- a/app/controllers/projects_controller.rb
+++ b/app/controllers/projects_controller.rb
@@ -15,29 +15,30 @@ def index
 
   def create
     @project = Project.new(project_params)
-    @project.user_id = current_user.id
-
-
+    @project.user = current_user
+    @users = User.all
+ 
     if @project.save
       #associate_project_with_todos!
       associate_project_with_assignees!
 
       SlackNotifier.notify("프로젝트 추가되었어용 : #{@project.title} (#{Rails.application.routes.url_helpers.project_url(@project)})")
       MailSender.send_email_when_create(current_user.email, @project)
+      redirect_to projects_path
+    else
+      flash[:error] = @project.errors.full_messages.join('\n')
+      render 'new'
     end
-    redirect_to projects_path
   end
   
   def detail
     @project = Project.find(params[:id])
-    
   end
 
   def show
     @todo = Todo.new    
     @todos = Todo.where(project_id: params[:id])
     @histories = History.where(project_id: params[:id])
-    
   end
 
   def edit
@@ -48,6 +49,7 @@ def edit
 
   def update
     @project = Project.find(params[:id])
+    @users = User.all
 
     if @project.update(project_params)
       #associate_project_with_todos!
@@ -56,6 +58,7 @@ def update
       SlackNotifier.notify("프로젝트가 수정되었어용 : #{@project.title} (#{Rails.application.routes.url_helpers.project_url(@project)})")
       redirect_to @project
     else
+      flash[:error] = @project.errors.full_messages.join('\n')
       render 'edit'
     end
   end
diff --git a/app/models/comment.rb b/app/models/comment.rb
index 6be5b17..9d05d8f 100644
--- a/app/models/comment.rb
+++ b/app/models/comment.rb
@@ -1,4 +1,7 @@
 class Comment < ActiveRecord::Base
   belongs_to :user
   belongs_to :history
+
+  validates :contents, presence: true
+  validates :user, presence: true
 end
diff --git a/app/models/history.rb b/app/models/history.rb
index 684bf60..fd97b74 100644
--- a/app/models/history.rb
+++ b/app/models/history.rb
@@ -22,6 +22,10 @@ class History < ActiveRecord::Base
   has_many :inverse_history_histories, class_name: "HistoryHistory", foreign_key: "referencing_history_id"
   has_many :referenced_histories, through: :inverse_history_histories, source: :history
 
+  validate :user, presence: true
+  validate :project, presence: true
+  validate :title, presence: true
+
   include PublicActivity::Model
   tracked :except => :destroy
   has_many :activities, as: :trackable, class_name: 'PublicActivity::Activity', dependent: :destroy
diff --git a/app/models/project.rb b/app/models/project.rb
index 30e7d47..8b7d041 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -3,8 +3,11 @@ class Project < ActiveRecord::Base
   has_many :assignees, through: :project_users
 	
 	belongs_to :user
-  has_many :todos
-  has_many :histories
+  has_many :todos, inverse_of: :project
+  has_many :histories, inverse_of: :project
+
+  validates :user, presence: true
+  validates :title, presence: true, uniqueness: { scope: :user }
 
   def fetch_members_by_nickname(nickname, count)
     members = assignees.arel_table
diff --git a/app/models/todo.rb b/app/models/todo.rb
index dd1e481..e8b1d41 100644
--- a/app/models/todo.rb
+++ b/app/models/todo.rb
@@ -6,6 +6,10 @@ class Todo < ActiveRecord::Base
   has_many :histories, through: :history_todos
   belongs_to :user
   belongs_to :project
+
+  validates :project, presence: true
+  validates :user, presence: true
+  validates :title, presence: true
   
   def self.fetch_list_from(id, count)
     where(arel_table[:id].gteq(id)).take(count)
diff --git a/app/models/user.rb b/app/models/user.rb
index 9715d4e..cfe6306 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -1,8 +1,10 @@
 class User < ActiveRecord::Base
   # Include default devise modules. Others available are:
   # :confirmable, :lockable, :timeoutable and :omniauthable
-  has_many :histories
-  has_many :todos
+  has_many :histories, inverse_of: :user
+  has_many :todos, inverse_of: :user
+  has_many :projects, inverse_of: :user
+  has_many :comments, inverse_of: :user
 
   has_many :history_users, foreign_key: :assignee_id
   has_many :assigned_histories, through: :history_users  
@@ -12,13 +14,11 @@ class User < ActiveRecord::Base
 
   belongs_to :user
 
-  belongs_to :comment
   devise :database_authenticatable, :registerable,
   :recoverable, :rememberable, :trackable, :validatable,
   :omniauthable, :omniauth_providers => [:facebook, :google_oauth2, :twitter]
 
-  validates_presence_of :nickname
-  validates_uniqueness_of :nickname
+  validates :nickname, uniqueness: true, presence: true
 
   acts_as_reader