Ruby on Rails：未定義的方法`model_name'爲NilClass：類

Question

我想讓用戶輸入一個項目到數據庫中。其中一個領域允許他們爲該項目輸入多種技術。

這是我的項目控制器，新建並創建動作。

def new 
    @project = Project.new 
    @all_technols = Technol.all 
    @project_technol = @project.projecttechnols.build 

    respond_to do |format| 
    format.html # new.html.erb 
    format.json { render json: @project } 
    end 
end 

def create 
    @project = Project.new(params[:project]) 
    params[:technols][:id].each do |technol| 
    if !technol.empty? 
     @project.projecttechnols.build(:technol_id => technol) 
    end 
    end 
end 

這是我的多選技術下拉菜單的新項目視圖。

<%= fields_for(@project_technol) do |ab| %> 
    <div class="tech"> 
    <%= ab.label "All Tech" %><br/> 
    <%= collection_select(:technols, :id, @all_technols, :id, :tech, {}, {:multiple => true}) %> 
    </div> 
<% end %> 

project.rb

class Project < ActiveRecord::Base 
    attr_accessible :tech 
    has_many :projecttechnols 
    has_many :technols, :through => :projecttechnols 
end 

technol.rb

class Technol < ActiveRecord::Base 
    attr_accessible :tech 
    has_many :projecttechnols 
    has_many :projects, :through => :projecttechnols 
end 

projecttechnol.rb

class Projecttechnol < ActiveRecord::Base 
    attr_accessible :project_id, :technol_id 
    belongs_to :technol 
    belongs_to :project 
end 

目前，我有一個用戶可以輸入新技術的頁面。但是我想將這個選項移到創建新項目頁面，在那裏他們可以選擇現有的技術，或者輸入一個新的項目，或者兩者兼而有之，然後他們可以保存這個項目。

但是，當我嘗試保存新項目時，出現此錯誤。

Showing /home/james/Desktop/webapp/app/views/projects/new.html.erb where line #233 raised: 

    undefined method `model_name' for NilClass:Class 

Extracted source (around line #233): 

233: <%= fields_for(@project_technol) do |ab| %> 
234: 
235: <div class="tech"> 
236: <%= ab.label "All Tech" %><br/> 

我是新來的鐵路，仍然在學習，所以請記住，當回答。提前致謝。編輯

改變

@project.projecttechnols.build(:technol_id => technol) 

到

@project_technol = @project.projecttechnols.build(:technol_id => technol) 

後

現在我得到這個錯誤：

NoMethodError in Projects#create 

undefined method `map' for nil:NilClass 

Extracted source (around line #240): 

237: <div class="tech"> 
238: <%= ab.label "All Tech" %><br/> 
239: 
240: <%= collection_select(:technols, :id, @all_technols, :id, :tech, {}, {:multiple => true}) %> 
241: </div> 
242: <% end %> 

個EDIT 2個

@all_technols = Technol.all在創建行動

現在我得到這個錯誤。

NoMethodError in Projects#show 

Showing /home/james/Desktop/webapp/app/views/projects/show.html.erb where line #181 raised: 

undefined method `technol' for #<Project:0xb36823c> 
Extracted source (around line #181): 

178: <h3>Related books</h3> 
179: 
180: <ul> 
181: <% @project.technol.each do |technol| %> 
182:  <li><%= technol.tech %> <%= link_to "Details", technol_path(technol) %></li> 
183: <% end %> 
184: </ul> 

Answer 1

您的create操作將再次呈現new視圖。但是，@project_technol未在create操作中定義。 fields_for方法調用model_name方法中傳遞的參數（@project_technol），但自從@project_technol = nil，它拋出該錯誤。爲了解決這個問題，您create操作中，改變

@project.projecttechnols.build(:technol_id => technol) 

到

@project_technol = @project.projecttechnols.build(:technol_id => technol)