Javascript Rails 4、Ajax导致404和500错误

我正在学习Michael Hartl的Rails教程，，在完全按照指导学习了他的教程之后，我遇到了一个奇怪的404/500错误

我对这个错误了解得不够，不知道如何修复它

尝试从标准跟随和取消跟随按钮切换到启用Ajax的跟随/取消跟随按钮时，会发生此错误

follow按钮只会重复产生500个错误。（见图）

单击以下按钮后，服务器控制台如下所示：

Started POST "/relationships" for ::1 at 2015-11-21 10:42:41 -0500
Processing by RelationshipsController#create as JS
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"nUhePXUdztraIcRVmQ6ewMjzLBPLbCJKjvGUExoQu7XH+zTJYj9J/+wopP7kAI1ycAa5t0bG7fEuApgAQqcDDw==", "followed_id"=>"4", "commit"=>"Follow"}
  User Load (0.2ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 1]]
  User Load (0.2ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 4]]
   (0.1ms)  begin transaction
  SQL (0.5ms)  INSERT INTO "relationships" ("followed_id", "follower_id", "created_at", "updated_at") VALUES (?, ?, ?, ?)  [["followed_id", 4], ["follower_id", 1], ["created_at", "2015-11-21 15:42:41.359403"], ["updated_at", "2015-11-21 15:42:41.359403"]]
   (3.4ms)  commit transaction
  Rendered users/_unfollow.html.erb (7.6ms)
  Rendered relationships/create.js.erb (10.4ms)
Completed 500 Internal Server Error in 35ms (ActiveRecord: 4.6ms)

NoMethodError (undefined method `id' for nil:NilClass):
  app/views/users/_unfollow.html.erb:1:in `_app_views_users__unfollow_html_erb__4478734189885612533_2206022220'
  app/views/relationships/create.js.erb:1:in `_app_views_relationships_create_js_erb___3841425439351308004_2234925000'
  app/controllers/relationships_controller.rb:8:in `create'

Started DELETE "/relationships/106" for ::1 at 2015-11-21 10:44:16 -0500
Processing by RelationshipsController#destroy as JS
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"MQQWiFHmikzre6tgsaVNf25z1r4Ps4yMhiX6BVAHvWFrt3x8RsQNad1yy8vMq17N1oZDGoIZQzcm1vYWCLAF2w==", "commit"=>"Unfollow", "id"=>"106"}
  User Load (0.2ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 1]]
  Relationship Load (0.2ms)  SELECT  "relationships".* FROM "relationships" WHERE "relationships"."id" = ? LIMIT 1  [["id", 106]]
  User Load (0.2ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 4]]
  Relationship Load (0.6ms)  SELECT  "relationships".* FROM "relationships" WHERE "relationships"."follower_id" = ? AND "relationships"."followed_id" = ? LIMIT 1  [["follower_id", 1], ["followed_id", 4]]
   (0.4ms)  begin transaction
  SQL (1.3ms)  DELETE FROM "relationships" WHERE "relationships"."id" = ?  [["id", 106]]
   (571.2ms)  commit transaction
  Rendered users/_follow.html.erb (7.3ms)
  Rendered relationships/destroy.js.erb (10.0ms)
Completed 500 Internal Server Error in 608ms (ActiveRecord: 574.0ms)

NoMethodError (undefined method `id' for nil:NilClass):
  app/views/users/_follow.html.erb:2:in `block in _app_views_users__follow_html_erb__4224173111585839618_2218160400'
  app/views/users/_follow.html.erb:1:in `_app_views_users__follow_html_erb__4224173111585839618_2218160400'
  app/views/relationships/destroy.js.erb:1:in `_app_views_relationships_destroy_js_erb___1536758446230344516_2256927580'
  app/controllers/relationships_controller.rb:18:in `destroy'

第一次单击unfollow按钮时会产生500错误，然后在随后按下404错误。（见图）

单击unfollow按钮后，服务器控制台如下所示：

Started POST "/relationships" for ::1 at 2015-11-21 10:42:41 -0500
Processing by RelationshipsController#create as JS
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"nUhePXUdztraIcRVmQ6ewMjzLBPLbCJKjvGUExoQu7XH+zTJYj9J/+wopP7kAI1ycAa5t0bG7fEuApgAQqcDDw==", "followed_id"=>"4", "commit"=>"Follow"}
  User Load (0.2ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 1]]
  User Load (0.2ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 4]]
   (0.1ms)  begin transaction
  SQL (0.5ms)  INSERT INTO "relationships" ("followed_id", "follower_id", "created_at", "updated_at") VALUES (?, ?, ?, ?)  [["followed_id", 4], ["follower_id", 1], ["created_at", "2015-11-21 15:42:41.359403"], ["updated_at", "2015-11-21 15:42:41.359403"]]
   (3.4ms)  commit transaction
  Rendered users/_unfollow.html.erb (7.6ms)
  Rendered relationships/create.js.erb (10.4ms)
Completed 500 Internal Server Error in 35ms (ActiveRecord: 4.6ms)

NoMethodError (undefined method `id' for nil:NilClass):
  app/views/users/_unfollow.html.erb:1:in `_app_views_users__unfollow_html_erb__4478734189885612533_2206022220'
  app/views/relationships/create.js.erb:1:in `_app_views_relationships_create_js_erb___3841425439351308004_2234925000'
  app/controllers/relationships_controller.rb:8:in `create'

Started DELETE "/relationships/106" for ::1 at 2015-11-21 10:44:16 -0500
Processing by RelationshipsController#destroy as JS
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"MQQWiFHmikzre6tgsaVNf25z1r4Ps4yMhiX6BVAHvWFrt3x8RsQNad1yy8vMq17N1oZDGoIZQzcm1vYWCLAF2w==", "commit"=>"Unfollow", "id"=>"106"}
  User Load (0.2ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 1]]
  Relationship Load (0.2ms)  SELECT  "relationships".* FROM "relationships" WHERE "relationships"."id" = ? LIMIT 1  [["id", 106]]
  User Load (0.2ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 4]]
  Relationship Load (0.6ms)  SELECT  "relationships".* FROM "relationships" WHERE "relationships"."follower_id" = ? AND "relationships"."followed_id" = ? LIMIT 1  [["follower_id", 1], ["followed_id", 4]]
   (0.4ms)  begin transaction
  SQL (1.3ms)  DELETE FROM "relationships" WHERE "relationships"."id" = ?  [["id", 106]]
   (571.2ms)  commit transaction
  Rendered users/_follow.html.erb (7.3ms)
  Rendered relationships/destroy.js.erb (10.0ms)
Completed 500 Internal Server Error in 608ms (ActiveRecord: 574.0ms)

NoMethodError (undefined method `id' for nil:NilClass):
  app/views/users/_follow.html.erb:2:in `block in _app_views_users__follow_html_erb__4224173111585839618_2218160400'
  app/views/users/_follow.html.erb:1:in `_app_views_users__follow_html_erb__4224173111585839618_2218160400'
  app/views/relationships/destroy.js.erb:1:in `_app_views_relationships_destroy_js_erb___1536758446230344516_2256927580'
  app/controllers/relationships_controller.rb:18:in `destroy'

在Chrome developer tools中，显示触发错误的代码如下：

xhr.send( ( options.hasContent && options.data ) || null );

我将把问题分为以下两部分。。。添加启用ajax的按钮之前的工作，以及开始产生错误的代码添加

---

正在工作：标准按钮 这就是切换到Ajax之前的工作：

关系\u controller.rb

class RelationshipsController < ApplicationController
  before_action :logged_in_user

  def create
    user = User.find(params[:followed_id])
    current_user.follow(user)
    redirect_to user
  end

  def destroy
    user = Relationship.find(params[:id]).followed
    current_user.unfollow(user)
    redirect_to user
  end
end

<%= form_for(current_user.active_relationships.build) do |f| %>
  <div><%= hidden_field_tag :followed_id, @user.id %></div>                        
  <%= f.submit "Follow", class: "btn btn-primary" %>
<% end %>

<%= form_for(current_user.active_relationships.find_by(followed_id: @user.id),
             html: { method: :delete }) do |f| %>
  <%= f.submit "Unfollow", class: "btn" %>
<% end %>

require 'test_helper'

class FollowingTest < ActionDispatch::IntegrationTest

  def setup
    @user  = users(:michael)
    @other = users(:archer)
    log_in_as(@user)
  end

  test "following page" do
    get following_user_path(@user)
    assert_not @user.following.empty?
    assert_match @user.following.count.to_s, response.body
    @user.following.each do |user|
      assert_select "a[href=?]", user_path(user)
    end
  end

  test "followers page" do
    get followers_user_path(@user)
    assert_not @user.followers.empty?
    assert_match @user.followers.count.to_s, response.body
    @user.followers.each do |user|
      assert_select "a[href=?]", user_path(user)
    end
  end

  test "should follow a user the standard way" do
    assert_difference '@user.following.count', 1 do
      post relationships_path, followed_id: @other.id
    end
  end

  test "should follow a user with Ajax" do
    assert_difference '@user.following.count', 1 do
      xhr :post, relationships_path, followed_id: @other.id
    end
  end

  test "should unfollow a user the standard way" do
    @user.follow(@other)
    relationship = @user.active_relationships.find_by(followed_id: @other.id)
    assert_difference '@user.following.count', -1 do
      delete relationship_path(relationship)
    end
  end

  test "should unfollow a user with Ajax" do
    @user.follow(@other)
    relationship = @user.active_relationships.find_by(followed_id: @other.id)
    assert_difference '@user.following.count', -1 do
      xhr :delete, relationship_path(relationship)
    end
  end
end

<%= form_for(current_user.active_relationships.build, remote: true) do |f| %>
  <div><%= hidden_field_tag :followed_id, @user.id %></div>
  <%= f.submit "Follow", class: "btn btn-primary" %>
<% end %>

<%= form_for(current_user.active_relationships.find_by(followed_id: @user.id),
             html: { method: :delete },
             remote: true) do |f| %>
  <%= f.submit "Unfollow", class: "btn" %>
<% end %>

class RelationshipsController < ApplicationController
  before_action :logged_in_user

  def create
    @user = User.find(params[:followed_id])
    current_user.follow(@user)
    respond_to do |format|
      format.html { redirect_to @user }
      format.js
    end
  end

  def destroy
    @user = Relationship.find(params[:id]).followed
    current_user.unfollow(@user)
    respond_to do |format|
      format.html { redirect_to @user }
      format.js
    end
  end
end

$("#follow_form").html("<%= escape_javascript(render('users/unfollow')) %>");
$("#followers").html('<%= @user.followers.count %>');

$("#follow_form").html("<%= escape_javascript(render('users/follow')) %>");
$("#followers").html('<%= @user.followers.count %>');

---

官方教程的github在这里：

我有一个确切的问题。虽然您的代码片段反映了这一变化，但对我来说，问题是Hartl没有突出显示他在

relationships\u controller.rb

中所做的一项关键更改（他确实在本文中谈到了这一点，我在本教程的这一点上略过）

变化是

user

从常规变量变为实例变量。因此：

user = User.find(params[:followed_id])

变成

@user = User.find(params[:followed_id])

添加了该更改后，nil:NilClass的

ActionView:：Template:：Error:undefined方法“id”错误得到了解决