#<Comment 的未定义方法 `user_id='

Question

我尝试创建具有 3 个模型用户、帖子和评论的应用程序。他们 3 个模型 关联的“has_many”和“belongs_to”关联。但是我没有得到这样做，本来是来自用户的cmets，怎么办？

控制器 cmets_controller.Here 浏览器在第 5 行显示错误（未定义方法 `user_id=' for #

class CommentsController < ApplicationController
  def create
    @post = Post.find(params[:post_id])
    @comment = @post.comments.create(comment_params)
    @comment.user_id = current_user.id
    redirect_to post_path(@post)
  end

  private
    def comment_params
      params.require(:comment).permit(:body)
    end
end

模型注释.rb

class Comment < ActiveRecord::Base
  belongs_to :post
  belongs_to :user
end

模型用户.rb

class User < ActiveRecord::Base
has_many :posts
has_many :comments
end

模型 post.rb

class Post < ActiveRecord::Base
    belongs_to :user
    has_many :comments
end

shema.rb

ActiveRecord::Schema.define(version: 20141114150704) do

  create_table "comments", force: true do |t|
    t.text     "body"
    t.integer  "post_id"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  add_index "comments", ["post_id"], name: "index_comments_on_post_id"

  create_table "posts", force: true do |t|
    t.string   "title"
    t.text     "text"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "users", force: true do |t|
    t.string   "name"
    t.string   "email"
    t.datetime "created_at"
    t.datetime "updated_at"
    t.string   "password_digest"
    t.string   "remember_token"
  end

  add_index "users", ["remember_token"], name: "index_users_on_remember_token"

end

UPD 完整的错误跟踪

app/controllers/comments_controller.rb:5:in `create'
actionpack (4.1.6) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (4.1.6) lib/abstract_controller/base.rb:189:in `process_action'
actionpack (4.1.6) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (4.1.6) lib/abstract_controller/callbacks.rb:20:in `block in process_action'
activesupport (4.1.6) lib/active_support/callbacks.rb:113:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:113:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:229:in `block in halting'
activesupport (4.1.6) lib/active_support/callbacks.rb:229:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:229:in `block in halting'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `block in halting'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `block in halting'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `block in halting'
activesupport (4.1.6) lib/active_support/callbacks.rb:86:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:86:in `run_callbacks'
actionpack (4.1.6) lib/abstract_controller/callbacks.rb:19:in `process_action'
actionpack (4.1.6) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (4.1.6) lib/action_controller/metal/instrumentation.rb:31:in `block in process_action'
activesupport (4.1.6) lib/active_support/notifications.rb:159:in `block in instrument'
activesupport (4.1.6) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (4.1.6) lib/active_support/notifications.rb:159:in `instrument'
actionpack (4.1.6) lib/action_controller/metal/instrumentation.rb:30:in `process_action'
actionpack (4.1.6) lib/action_controller/metal/params_wrapper.rb:250:in `process_action'
activerecord (4.1.6) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (4.1.6) lib/abstract_controller/base.rb:136:in `process'
actionview (4.1.6) lib/action_view/rendering.rb:30:in `process'
actionpack (4.1.6) lib/action_controller/metal.rb:196:in `dispatch'
actionpack (4.1.6) lib/action_controller/metal/rack_delegation.rb:13:in `dispatch'
actionpack (4.1.6) lib/action_controller/metal.rb:232:in `block in action'
actionpack (4.1.6) lib/action_dispatch/routing/route_set.rb:82:in `call'
actionpack (4.1.6) lib/action_dispatch/routing/route_set.rb:82:in `dispatch'
actionpack (4.1.6) lib/action_dispatch/routing/route_set.rb:50:in `call'
actionpack (4.1.6) lib/action_dispatch/journey/router.rb:73:in `block in call'
actionpack (4.1.6) lib/action_dispatch/journey/router.rb:59:in `each'
actionpack (4.1.6) lib/action_dispatch/journey/router.rb:59:in `call'
actionpack (4.1.6) lib/action_dispatch/routing/route_set.rb:678:in `call'
rack (1.5.2) lib/rack/etag.rb:23:in `call'
rack (1.5.2) lib/rack/conditionalget.rb:35:in `call'
rack (1.5.2) lib/rack/head.rb:11:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/params_parser.rb:27:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/flash.rb:254:in `call'
rack (1.5.2) lib/rack/session/abstract/id.rb:225:in `context'
rack (1.5.2) lib/rack/session/abstract/id.rb:220:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/cookies.rb:560:in `call'
activerecord (4.1.6) lib/active_record/query_cache.rb:36:in `call'
activerecord (4.1.6) lib/active_record/connection_adapters/abstract/connection_pool.rb:621:in `call'
activerecord (4.1.6) lib/active_record/migration.rb:380:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
activesupport (4.1.6) lib/active_support/callbacks.rb:82:in `run_callbacks'
actionpack (4.1.6) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/reloader.rb:73:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/remote_ip.rb:76:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
railties (4.1.6) lib/rails/rack/logger.rb:38:in `call_app'
railties (4.1.6) lib/rails/rack/logger.rb:20:in `block in call'
activesupport (4.1.6) lib/active_support/tagged_logging.rb:68:in `block in tagged'
activesupport (4.1.6) lib/active_support/tagged_logging.rb:26:in `tagged'
activesupport (4.1.6) lib/active_support/tagged_logging.rb:68:in `tagged'
railties (4.1.6) lib/rails/rack/logger.rb:20:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/request_id.rb:21:in `call'
rack (1.5.2) lib/rack/methodoverride.rb:21:in `call'
rack (1.5.2) lib/rack/runtime.rb:17:in `call'
activesupport (4.1.6) lib/active_support/cache/strategy/local_cache_middleware.rb:26:in `call'
rack (1.5.2) lib/rack/lock.rb:17:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/static.rb:64:in `call'
rack (1.5.2) lib/rack/sendfile.rb:112:in `call'
railties (4.1.6) lib/rails/engine.rb:514:in `call'
railties (4.1.6) lib/rails/application.rb:144:in `call'
rack (1.5.2) lib/rack/lock.rb:17:in `call'
rack (1.5.2) lib/rack/content_length.rb:14:in `call'
rack (1.5.2) lib/rack/handler/webrick.rb:60:in `service'
/home/weare138/.rvm/rubies/ruby-2.1.2/lib/ruby/2.1.0/webrick/httpserver.rb:138:in `service'
/home/weare138/.rvm/rubies/ruby-2.1.2/lib/ruby/2.1.0/webrick/httpserver.rb:94:in `run'
/home/weare138/.rvm/rubies/ruby-2.1.2/lib/ruby/2.1.0/webrick/server.rb:295:in `block in start_thread'

对不起我的英语不好

Answer 1

您的迁移中没有 user_id。要解决此问题，您可以遵循以下任一方法：

解决方案一：

创建一个新的迁移：

$ rails g migration AddUseIdToComments user_id:integer

打开AddUseIdToComments迁移文件看是否有：

add_column :comments, :user_id, :integer

然后运行：

$ rake db:migrate

解决方案 2：

代替：

create_table "comments", force: true do |t|
  t.text     "body"
  t.integer  "post_id"
  t.datetime "created_at"
  t.datetime "updated_at"
end

改成：

create_table "comments", force: true do |t|
  t.text     "body"
  t.integer  "post_id"
  t.integer  "user_id"
  t.datetime "created_at"
  t.datetime "updated_at"
end

运行：

$ rake db:rollback # to rollback old migration 
$ rake db:migrate # re run it

我鼓励您像解决方案 1 中提到的那样创建一个新的迁移，因为将来如果您保持编辑现有迁移的习惯，那么您最终可能会遇到不良问题。

完成迁移更改后。您需要将 CommentsController 中的 create 方法更改为：

def create
  @post = Post.find(params[:post_id])
  @comment = @post.comments.create(comment_params)
  @comment.user_id = current_user.id
  if @comment.save
    redirect_to post_path(@post)
  else
    render :new
  end
end

您没有保存 @comment 对象。注意行@comment.save，它根据事务的状态（成功/失败）保存并返回真或假，并重定向到帖子路径或渲染new方法。

更新：从您的错误跟踪来看，您似乎没有定义 current_user。

见行：

@comment.user_id = current_user.id

如果 current_user 为 nil，那么您将获得未定义的方法 id 用于 nil 类。您需要确保 current_user 助手返回适当的用户实例而不是 nil。如果您正在使用任何身份验证库，例如 devise，那么这意味着您正在尝试在您的用户未登录时访问 current_user，即尚未建立会话。请确保在执行此操作之前登录。

Answer 2

由于您的 Comments 表中没有 user_id，请从您的 rails 应用程序文件夹中的终端执行以下命令以添加它

rails generate migration AddUseridToComments user_id:integer

这会将包含 user_id 的列添加到您的表 Comments

然后执行

rake db:migrate

将该列添加到您的生产或开发数据库中

之后应用程序应该能够找到user_id