Ruby on Rails從屬於表id的1個字段填充

Question

您好我是Ruby on Rails的新手。我創造了兩個模型品牌和產品。一個品牌可能與許多產品有關。我使用腳手架，因爲這是我們的講師期望我們在我們的項目中做的。

我試圖設置我的產品屏幕，這樣當你輸入產品時，你會得到一個可供選擇的品牌名稱的下拉列表。當您輸入產品詳情時，請選擇品牌名稱，然後點擊提交;所選波段名稱中的brand_id保存到product.brand_id表中。 （當我在控制器中設置has_many時，我相信brand_id是在產品表中自動創建的）。

我試着用collection_set做這件事，但我很苦惱。我嘗試過使用堆棧溢出的一些技巧，但沒有一個能夠工作，並且作爲我嘗試自己發佈帖子的最後一招。

在模型我增加了以下內容：

class Brand < ApplicationRecord 
    has_many :product 
    validates :brand_name, presence: true 
end 

class Product < ApplicationRecord 
    belongs_to :brand 
    validates :name, presence: true 
end 

從給予我明白了，這意味着產品表將有brand_id以及ID。

在產品控制器I加入下列：

class ProductsController < ApplicationController 
    before_action :set_product, only: [:show, :edit, :update, :destroy] 

    # GET /products 
    # GET /products.json 
    def index 
    @products = Product.all 
    end 

    # GET /products/1 
    # GET /products/1.json 
    def show 
    end 

    # GET /products/new 
    def new 
    @brand = Brand.all 
    @product = Product.new 
    end 
... more code ... 

在形式的產品視圖添加以下

<%= form_for(product) do |f| %> 
    <% if product.errors.any? %> 
    <div id="error_explanation"> 
     <h2><%= pluralize(product.errors.count, "error") %> prohibited this product from being saved:</h2> 

     <ul> 
     <% product.errors.full_messages.each do |message| %> 
     <li><%= message %></li> 
     <% end %> 
     </ul> 
    </div> 
    <% end %> 

    <div class="field"> 
    <%= f.label :name %> 
    <%= f.text_field :name %> 
    </div> 

    <div class="field"> 
    <%= f.label :model %> 
    <%= f.text_field :model %> 
    </div> 

    <div class="field"> 
    <%= f.label :price %> 
    <%= f.text_field :price %> 
    </div> 

    <div class="field"> 
    <%= f.label :vat %> 
    <%= f.text_field :vat %> 
    </div> 

    <div class="field"> 
    <%= f.label :image_uri %> 
    <%= f.text_field :image_uri %> 
    </div> 
    <div class="field"> 
     <%= f.collection_select :brand_id, @brand, :id, :brand_name %> 
    </div> 



    <div class="actions"> 
    <%= f.submit %> 
    </div> 
<% end %> 

的routes.rb

Rails.application.routes.draw do 
    resources :users 
    resources :products 
    resources :sales_orders 
    resources :payments 
    resources :filter_group_items 
    resources :filter_groups 
    resources :categories 
    resources :sales_order_lines 
    resources :brands 
    resources :addresses 
    get '/cart' => 'cart#index' 
    get '/products' => 'products#index' 
    get '/brands' => 'brands#index' 
    get '/users' => 'users#index' 
    get '/addresses' => 'addresses#index' 
    get '/payments' => 'payments#index' 

    # For details on the DSL available within this file, see http://guides.rubyonrails.org/routing.html 
    #root 'application#hello' 
    # You can have the root of your site routed with "root" 
    #root 'welcome#index' 
    root 'products#index' 
end 

我得到出現以下錯誤 顯示/ home/ubuntu/workspace/ssd_project/app/views/prod ucts/_form.html.erb在哪裏行＃40上升：

未定義的方法`brand_id'爲＃ 您的意思是？品牌

39 <div class="field"> 
40 <%= f.collection_select :brand_id, @brand, :id, :brand_name %> 
41 </div> 

模板包含的跟蹤：應用程序/視圖/產品/ new.html.erb

如果任何人有如何做到這一點，我會很感激的任何建議。

新的routes.rb

Rails.application.routes.draw do 
    resources :users 
    resources :products 
    resources :sales_orders 
    resources :payments 
    resources :filter_group_items 
    resources :filter_groups 
    resources :categories 
    resources :sales_order_lines 
    resources :brands 
    resources :addresses 

    resources :brands do 
     resources :products 
    end 

    get '/cart' => 'cart#index' 
    get '/products' => 'products#new' 
    get '/brands' => 'brands#index' 
    get '/users' => 'users#index' 
    get '/addresses' => 'addresses#index' 
    get '/payments' => 'payments#index' 



    # For details on the DSL available within this file, see http://guides.rubyonrails.org/routing.html 
    #root 'application#hello' 
    # You can have the root of your site routed with "root" 
    #root 'welcome#index' 
    root 'products#index' 
end 

數據庫架構schema.rb

# This file is auto-generated from the current state of the database. Instead 
# of editing this file, please use the migrations feature of Active Record to 
# incrementally modify your database, and then regenerate this schema definition. 
# 
# Note that this schema.rb definition is the authoritative source for your 
# database schema. If you need to create the application database on another 
# system, you should be using db:schema:load, not running all the migrations 
# from scratch. The latter is a flawed and unsustainable approach (the more migrations 
# you'll amass, the slower it'll run and the greater likelihood for issues). 
# 
# It's strongly recommended that you check this file into your version control system. 

ActiveRecord::Schema.define(version: 20160706122948) do 

    create_table "addresses", force: :cascade do |t| 
    t.string "line1" 
    t.string "line2" 
    t.string "line3" 
    t.string "country" 
    t.string "post_code" 
    t.datetime "created_at", null: false 
    t.datetime "updated_at", null: false 
    end 

    create_table "brands", force: :cascade do |t| 
    t.string "brand_name" 
    t.datetime "created_at", null: false 
    t.datetime "updated_at", null: false 
    end 

    create_table "categories", force: :cascade do |t| 
    t.string "name" 
    t.datetime "created_at", null: false 
    t.datetime "updated_at", null: false 
    end 

    create_table "filter_group_items", force: :cascade do |t| 
    t.string "description" 
    t.datetime "created_at", null: false 
    t.datetime "updated_at", null: false 
    end 

    create_table "filter_groups", force: :cascade do |t| 
    t.string "description" 
    t.datetime "created_at", null: false 
    t.datetime "updated_at", null: false 
    end 

    create_table "payments", force: :cascade do |t| 
    t.datetime "date" 
    t.decimal "amount" 
    t.datetime "created_at", null: false 
    t.datetime "updated_at", null: false 
    end 

    create_table "products", force: :cascade do |t| 
    t.string "name" 
    t.string "model" 
    t.decimal "price" 
    t.decimal "vat" 
    t.string "image_uri" 
    t.datetime "created_at", null: false 
    t.datetime "updated_at", null: false 
    end 

    create_table "sales_order_lines", force: :cascade do |t| 
    t.integer "qty" 
    t.decimal "price" 
    t.decimal "total" 
    t.datetime "created_at", null: false 
    t.datetime "updated_at", null: false 
    end 

    create_table "sales_orders", force: :cascade do |t| 
    t.datetime "date" 
    t.decimal "total" 
    t.decimal "vat" 
    t.datetime "created_at", null: false 
    t.datetime "updated_at", null: false 
    end 

    create_table "users", force: :cascade do |t| 
    t.string "name" 
    t.string "email" 
    t.string "password" 
    t.string "phone" 
    t.datetime "created_at",     null: false 
    t.datetime "updated_at",     null: false 
    t.boolean "admin_user", default: false 
    end 

end 

Answer 1

你試試這個：

<div class="field"> 
    <%= f.collection_select :brand_id, Brand.all, :id, :brand_name %> 
</div> 

第二個參數是一個集合，你可以得到所有可能的品牌與Brand.all

然後你就可以取出保存在產品控制線@brand = Brand.all新作用下

此外，在您的形式，我認爲你應該的form_for（@product），而不是產品。您想要實例變量@product

您的路線安排是否使產品嵌套在品牌下？也將有助於看到路線。這是另一個潛在的問題

編輯：

這將是一個嵌套的路線（您的應用沒有）的例子：

resources :brands do 
    resources :products 
end 

這將產生這樣的路線：

/品牌/：brand_id /產品/：ID

所以我重新創建你的應用程序，發現form_for(product)對我造成了錯誤。如果切換到實例變量@product（您已在控制器中設置），則代碼按預期工作。 form_for(@product)應該與您的產品控制器中的@product = Product.new匹配，即新操作。回顧一下，我關於如何做collection.select的另一個建議本質上是更具風格的，但我相信它會讓你的代碼更容易遵循。

第二個編輯：

你schema.rb文件顯示問題。即使您在模型中與has_many和belongs_to相關聯（與您認爲這不是自動發生的，而是通過數據庫遷移相反），產品表中不包含對品牌表的引用。問題是，產品表中缺少brand_id列

首先，我想UNNEST你的路由，這樣，就如前：

resources :products 
    resources :brands 

然後，你將需要運行遷移添加的品牌參考到產品表。在您的命令行中，使用命令rails generate migration add_reference_to_products，然後在您的遷移文件夾中（可在/ db/migrate中找到該文件夾​​），打開剛創建的遷移文件。將以下內容添加到您的def change區塊中：

def change 
    add_reference :products, :brand, index: true, foreign_key: true 
end 

請確保保存該文件。然後在您的命令行中輸入rake db:migrate來運行遷移。這將在您的產品表中創建一個brand_id的列，並且您的代碼應該可以工作