How to update unique fields using a confirm page? - ruby-on-rails

Question

So I have this book edit page which contains unique fields(Title, ISBN). But before I submit the form to update, I need to send first the form information to another confirmation page and then update. But when I pass the form info to the confirmation page, the unique validations for Title and ISBN fails. I have this code:
book.rb
validates :title, presence: true,
uniqueness: true
validates :isbn, presence: true,
uniqueness: true,
format: { with: /[0-9]/ }
edit.html.erb
<%= form_for #book, url: confirm_edit_admin_book_path, method: :patch, html: { class: "form" } do |f| %>
<%= f.hidden_field :id %>
<div class="float-right">
<button class="btn btn-primary">Confirm</button>
</div>
<h4 class="card-title">Edit Book</h4>
<div class="form-group row mt-5">
<%= f.label :title, class: "col-md-2 col-form-label required" %>
<div class="col-md-10">
<%= f.text_field :title, class: "form-control" %>
<%= render "admin/shared/error_field", field: :title %>
</div>
</div>
<div class="form-group row">
<%= f.label :isbn, "ISBN", class: "col-md-2 col-form-label required" %>
<div class="col-md-10">
<%= f.text_field :isbn, class: 'col-sm-12 form-control' %>
<%= render "admin/shared/error_field", field: :isbn %>
</div>
</div>
<div class="form-group row">
<%= f.label :released_at, class: "col-md-2 col-form-label required" %>
<div class="col-md-10">
<%= f.date_field :released_at, class: 'col-sm-12 form-control' %>
<%= render "admin/shared/error_field", field: :released_at %>
</div>
</div>
<div class="form-group row">
<%= f.label :description, class: "col-md-2 col-form-label" %>
<div class="col-md-10">
<%= f.text_area :description, class: 'col-sm-12 form-control' %>
<%= render "admin/shared/error_field", field: :description %>
</div>
</div>
<div class="form-group row">
<%= f.label :quantity, class: "col-md-2 col-form-label required" %>
<div class="col-md-10">
<%= f.number_field :quantity, class: 'col-sm-12 form-control' %>
<%= render "admin/shared/error_field", field: :quantity %>
</div>
</div>
<div class="float-right">
<%= f.submit "Confirm", class: "btn cur-p btn-primary" %>
</div>
<% end %>
books_controller.rb
def confirm_edit
#book = Book.new(book_params)
book_info = Book.find(#book.id)
if #book.valid?
session[:book_update] = #book
else
render 'edit'
end
end
def update
#book = Book.find(params[:id])
#book.update_attributes(session[:book_update].compact)
session.delete(:book_update)
redirect_to admin_book_url
end

Answer 1

In the confirm_edit action you are creating a new instance of Book using the params from the update action, which are presumably the params from an existing book.
#book = Book.new(book_params)
You are then calling #book.valid? which is going to fail (unless you've changed the Title and ISBN) because a book with the same values is already in the database.
You could retrieve the book from the database and then use .assign_attributes to check validity that way perhaps?
def confirm_edit
#book = Book.find(params[:id])
#book.assign_attributes(book_params)
if #book.valid?
session[:book_update] = #book
else
render 'edit'
end
end