ruby-on-rails - 将用户模型中的整数递增/递减 1

Question

我有一个用户模型，其中包含这些列 - name、email、books_on_loan

我有一个预订系统，用户可以在其中 checkout /借阅书籍。当用户 checkout 一本书时，我想将他们的 'books_on_loan_ 整数增加一个，反之亦然。

到目前为止，我已经这样尝试过了，但收到错误消息“undefined method `+' for nil:NilClass”——它不喜欢 @user.books_on_loan

def check_out

  @params = params[:book]
  title = @params[:title]
  name = @params[:name]
  @book = Book.find_by_title(title)
  @user = User.find_by_name(name)




 if @user == nil
   @note = 'This user is not registered.'
 elsif @book == nil
   @note = 'This book is not in the library.'
 elsif @book.onloan == 1
   @note = 'This book is on loan.'
 elsif @user.books_on_loan == 3
   @note = 'This user already has 3 books out.'

else
  @book.onloan = 1
  @book.save
  @books_loaned = BooksOnloan.create(book_id: @book.id, user_id: @user.id)
  @books_loaned.save
  @user.books_on_loan = @user.books_on_loan + 1
  @user.save
  @note = 'The book was checked out.'
end
respond_to do |format|
  format.html    
  end    
end

Answer 1

试试这个:

@user.increment :books_on_loan, 1