Ruby Rails Has_Many fetching data

I am trying to fetch the information from books associated with a
customer but seem that the middle association doesn't works

Here my model

Book
    has_many :book_managers
    has_many :customers, :through => :book_managers

Customer
    has_many :book_managers
        has_many :books, :through => :book_managers

Book_Manager
    belongs_to :customer
    belongs_to :book
The field are has follow

Book Customer book_manager
id id id
description email customer_id
              password book_id
              first visible
              last
When fetching the information in my def edit, the following is
successfull

@book = Book.first
@book = Book.last
The following seem to fails

@customer = Customer.find(params[:id])
@book = @customer.books.first
@book = @customer.books.order("created_at DESC").first
Is there something i miss?

I also try to verify by creating an index for book_manager controller
and view and nothing appears, its seems its empty. The way i created the
books was as follow

BookController

def create
@book = current_customer.books.build(params[:book])
    if @book.save
        flash[:success] = "Book Created"
        redirect_to root_url
    else
        render 'customer/edit'
    end
end