如何在Ruby中定義此方法？

我真的堅持這個錯誤，並希望有人幫我解決它。所以，我用這個幫手：如何在Ruby中定義此方法？

module BooksHelper 
    def image_from_amazon(amazon_id) 
     image_tag "http://images.amazon.com/images/P/#{amazon_id}.01.ZTZZZZZZ.jpg" 
    end 
end

查看文件

> <%= image_from_amazon(book.amazon_id) %>

在我的本地機器一切，除了Heroku的正常工作。日誌：

> ActionView::Template::Error (undefined method `amazon_id' for #<Book:0x007f06994ea498>): 
2015-08-18T16:28:19.320038+00:00 app[web.1]:  7: <% @books.each do |book| %> 
2015-08-18T16:28:19.320040+00:00 app[web.1]:  8: <div class="book"> 
2015-08-18T16:28:19.320041+00:00 app[web.1]:  9: <div class="cover"> 
2015-08-18T16:28:19.320042+00:00 app[web.1]:  10:  <%= image_from_amazon(book.amazon_id) %> 
2015-08-18T16:28:19.320044+00:00 app[web.1]:  11: </div> 
2015-08-18T16:28:19.320045+00:00 app[web.1]:  12: <div class="content"> 
2015-08-18T16:28:19.320047+00:00 app[web.1]:  13:  <h4 class="title"><%= link_to book.title, book %></h4> 
2015-08-18T16:28:19.320048+00:00 app[web.1]: app/views/books/index.html.erb:10:in `block in _app_views_books_index_html_erb__843408363563836431_69833158224880' 
2015-08-18T16:28:19.320050+00:00 app[web.1]: app/views/books/index.html.erb:7:in `_app_views_books_index_html_erb__843408363563836431_69833158224880'

來源

2015-08-18 Hola

書的表是否有亞馬遜ID字段？你有沒有在heroku上進行遷移？ – coderhs

是的，我做了「heroku運行耙db：遷移」，但它並沒有幫助。「heroku運行耙db：設置」 - 幫助我。所以爲什麼？每次部署後我應該創建一個新的數據庫嗎？ – Hola

此行是關鍵：

> ActionView::Template::Error (undefined method `amazon_id' for #<Book:0x007f06994ea498>):

你book實例並不amazon_id迴應。嘗試檢查值，例如

puts "amazon_id: #{book.try(:amazon_id)}"

來源

2015-08-18 23:23:14 Mori

如何在Ruby中定義此方法？

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