Question

在“Beginning Rails 4”一书的第6章中遇到一些问题

表架构

ActiveRecord::Schema.define(version: 20160304183431) do

  create_table "articles", force: :cascade do |t|
    t.string   "title"
    t.text     "body"
    t.datetime "published_at"
    t.datetime "created_at",   null: false
    t.datetime "updated_at",   null: false
    t.string   "excerpt"
    t.string   "location"
    t.integer  "user_id"
  end

  create_table "articles_categories", id: false, force: :cascade do |t|
    t.integer "article_id"
    t.integer "category_id"
  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 "profiles", force: :cascade do |t|
    t.integer  "user_id"
    t.string   "name"
    t.date     "birthday"
    t.text     "bio"
    t.string   "color"
    t.string   "twitter"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end

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

end

用这个播种了seed.rb文件：

user = User.create :email => 'mary@example.com', :password => 'guessit'
Category.create [{:name => 'Programming'},
                 {:name => 'Event'},
                 {:name => 'Travel'},
                 {:name => 'Music'},
                 {:name => 'TV'}]

然后进入控制台：

 article = Article.last
 #<Article id: 5, title: "Advanced Active Record", body: "Models need to relate to each other. In the real w...", published_at: "2016-03-03 00:00:00", created_at: "2016-03-04 06:35:27", updated_at: "2016-03-04 06:35:27", excerpt: nil, location: nil, user_id: nil>
 category = Category.find_by_name('Programming')
 #<Category id: 1, name: "Programming", created_at: "2016-03-04 18:40:57", updated_at: "2016-03-04 18:40:57">
 article.categories << category

这是让我遇到麻烦的最后一行。每当我尝试article.categories << category时，我都会每次收到此消息：NoMethodError: undefined method categories' for #<Article:0x007fdbc333a328>

为什么呢？

编辑

文章模型

class Article < ActiveRecord::Base
    validates_presence_of :title, :body

    belongs_to :user
    has_and_belongs_to_many :categories

    def long_title
        "#{title} - #{published_at}"
    end

end

类别模型

class Category < ActiveRecord::Base
    has_and_belongs_to_many :articles
end

Answer 1

除了这张表

create_table "articles_categories", force: :cascade do |t|
  t.integer "article_id"
  t.integer "category_id"
end

您还需要一个索引：

add_index "articles_categories", ["article_id", "category_id"], name: "index_articles_categories_on_article_id_and_category_id", unique: true, using: :btree

通过这种方式，rails的魔力将能够链接您的文章和类别。可能会有一些拼写错误，但你明白了。

Rails控制台中的NoMethodError

1 个答案: