为什么我会收到错误“未定义的方法 'map'”？

Question

在我的 Ruby on Rails 应用程序中，我试图在 _form.html.erb 中显示三个下拉菜单，这些下拉菜单是从文件 _booking_lookup.html.erb 呈现的，并从模型中的下拉菜单方法中获取数据.

_form.html.erb：

<%= render(:partial => '/booking_lookup', :locals=> {:film => @film = Film.all, :showings => @showings = Showing.all, :seats => @seats = Seat.all, :my_path => '/films/booking_lookup' }) %>

_booking_lookup.html.erb：

<%= form_tag my_path, :method=>'post', :multipart => true do %>
<%= select_tag ('title_id'), 
    options_from_collection_for_select(@films, :id, :title_info, 0 ),
    :prompt => "Film" %>

<%= select_tag ('showings_id'), 
    options_from_collection_for_select(@showings, :id, :showing_times, 0 ),
    :prompt => "Showings" %> 

<%= select_tag ('seat_id'), 
    options_from_collection_for_select(@seats, :id, :seats_available, 0 ),
    :prompt => "Seats" %> 

<%= submit_tag 'Search' %>

电影.rb：

class Film < ActiveRecord::Base

has_many :showings
belongs_to :certificate
belongs_to :category

def title_info
     "#{title}"
end
end

座位.rb：

class Seat < ActiveRecord::Base
belongs_to :screen
has_many :bookings

def seats_available
    "#{row_letter}#{row_number}"
end
end

显示.rb：

 class Showing < ActiveRecord::Base
  belongs_to :film
  has_many :bookings
  belongs_to :screen

    def showing_times
        "#{show_date.strftime("%e %b %Y")} @ #{show_time.strftime("%H:%M")}"
    end
end

但由于某种原因，这条线：<%= select_tag ('title_id'), options_from_collection_for_select(@films, :id, :title_info, 0 ), :prompt => "Film" %> 我得到了错误：

NoMethodError in Bookings#new 
undefined method `map' for nil:NilClass

奇怪的是我在其他地方使用了很多这样的代码，我有一个 _multi_search.html.erb 表单：

 <%= form_tag my_path, :method=>'post', :multipart => true do %>
 <!--  Genre: -->
 Search By:
 <%= select_tag ('cat_id'), 
    options_from_collection_for_select(@categories, :id, :category_info, 0 ),
    :prompt => "Genre" %>

<%= select_tag ('cert_id'), 
    options_from_collection_for_select(@certificates, :id, :certificate_info, 0 ),
    :prompt => "Age Rating" %> 

<%= text_field_tag :search_string, nil, placeholder: "ACTOR" %>
or
<%= select_tag ('title_id'), 
    options_from_collection_for_select(@films, :id, :title_info, 0 ),
    :prompt => "Film" %>
<%= submit_tag 'Search' %>
<% end %>

并且在application.html.erb中使用：

<%= render(:partial => '/multi_search', :locals=> {:categories => @categories = existing_genres, :certificates => @certificates = Certificate.all, :films => @films = Film.all, :my_path => '/films/multi_find' }) %>

而且效果很好。

我做错了什么？

Answer 1

看起来@films 为零。尝试在 _form.html.erb 中设置@films = Film.all（而不是@film = Film.all）。

更新：

我建议将查询移至控制器操作。在模型-视图-控制器模式中，控制器应该向模型而不是视图询问数据。

# BookingLookupController
def new
  @films = Film.all
  @showings = Showing.all
  @seats = Seat.all
end

然后您可以在视图中引用实例变量。

<%= render partial: '/booking_lookup', locals: {films: @films, showings: @showings, seats: @seats, my_path: '/films/booking_lookup' } %>

Answer 2

在 Controller 中，选择您只想在下拉列表中显示名称的字段

def method_name
   @films = Film.select([:id, :title_info])
   @showings = Showing.select([:id, :showing_times])
   @seats = Seat.select([:id, :seats_available])
end

在页面中

<%= render(:partial => '/booking_lookup', :locals=> {:films => @films, :showings => @showings, :seats => @seats, :my_path => '/films/booking_lookup' }) %>

部分

 options_from_collection_for_select(films, :id, :title_info, 0 ),:prompt => "Film" %>