Ruby On rails validations

I am new to Rails.

I Have create a simple rails page which accepts bookid, title and publisher

rails generate scaffold book bookid:string title:string publisher:string

I have written a new search.html.erb and a defination to it which search for books by title.

Now my Question is how do i give a custom message if that book details doesn't exist in database.

Ex : I gave book name as rails it doesn't have any entry in my database

it should give message No Such Books