Ruby Rails: Form application - Validation failed - ruby-on-rails

Question

I am trying to follow this tutorial. It has written in previous version of Rails and I am using Rails 4. In section "Creating view file for new method" I have updated given code sample to work with current Rails but I am getting following error:
ActiveRecord::RecordInvalid in BookController#create
Validation failed: Title can't be blank, Price Error Message
Extracted source (around line #14):
12 def create
13 #book = Book.new(book_params)
14 if #book.save!
15 redirect_to :action => 'list'
16 else
17 #subjects = Subject.all
Rails.root: C:/Ruby193/mylibrary
Application Trace | Framework Trace | Full Trace
app/controllers/book_controller.rb:14:in `create'
Request
Parameters:
{"utf8"=>"✓",
"authenticity_token"=>"Xla1xJlMqCx96ZITbI6JHOvoNIoAHc5ItcZgcMzs0/Y=",
"title"=>"asd",
"price"=>"asd",
"book"=>{"subject_id"=>"1"},
"description"=>"asd",
"commit"=>"Create",
"method"=>"post"}
Here is my routing file:
Rails.application.routes.draw do
get 'book/list' => 'book#list'
get 'book/new' => 'book#new'
post 'book/create' => 'book#create'
end
Here is my controller class:
class BookController < ApplicationController
def list
#books = Book.all
end
def show
#book = Book.find(params[:id])
end
def new
#book = Book.new
#subjects = Subject.all
end
def create
#book = Book.new(book_params)
if #book.save!
redirect_to :action => 'list'
else
#subjects = Subject.all
render :action => 'new'
end
end
def edit
#book = Book.find(params[:id])
#subjects = Subject.all
end
def update
#book = Book.find(params[:id])
if #book.update_attributes(book_params)
redirect_to :action => 'show', :id => #book
else
#subjects = Subject.all
render :action => 'edit'
end
end
def delete
Book.find(params[:id]).destroy
redirect_to :action => 'list'
end
private
def book_params
params.require(:book).permit(:title, :price, :description)
end
end
Here is view- new.html
<h1>Add new book</h1>
<%= form_tag(controller: "book", action: "create", method: "post") do %>
<%= label_tag(:title, "Title") %>
<%= text_field_tag(:title) %><br>
<%= label_tag(:price, "Price") %>
<%= text_field_tag(:price) %><br>
<%= label_tag(:q, "Subject") %>
<%= collection_select(:book,:subject_id,#subjects,:id,:name) %><br>a
<%= label_tag(:description, "Description") %><br>
<%= text_area_tag(:description) %><br>
<%= submit_tag( "Create") %>
<%end %>
<%= link_to 'Back', {:action => 'list'} %>
What should I do? Thank you in advance

Answer 1

You need to change your form to properly place the :title attribute underneath the book key in your params. There are other helpers that let you do this:
Try changing lines like:
label_tag( :title )
text_field_tag(:title)
to
label( :book, :title )
text_field(:book, :title )

Answer 2

In your create method use save rather than save!
save! will throw validation errors in the manner you are seeing, save will add error messages to the #book object so that the user can fix them in a form.
See the documentation for details.
def create
#book = Book.new(book_params)
if #book.save
redirect_to :action => 'list'
else
#subjects = Subject.all
render :action => 'new'
end
end