尝试使用回形针和 aws-sdk gem 发布图像时出现 NoMethodError（nil:NilClass 的未定义方法 `first'）

Question

我最近将回形针 gem 添加到我的网络应用程序中。然后我添加了 aws-sdk 以便我可以在我的应用程序的生产版本上上传图像，该版本位于 heroku 上。在配置完所有内容并尝试上传图像后，我得到了标准的 rails 错误页面，并进入了日志：

NameError (uninitialized constant Paperclip::Storage::S3::AWS):
app/controllers/pins_controller.rb:23:in `create'

我在网上搜索，发现这是 aws-sdk 版本 2 的问题，我不得不降级 gem。所以我将 gem 降级为使用版本 1，然后运行 ​​bundle install，用 git 提交我的更改，并将其推送到 heroku。

这一次，当我尝试将照片附加到图钉时，我遇到了另一个错误。这让我相信之前的错误已修复，而我现在遇到了不同的问题。这是错误：

NoMethodError (undefined method `first' for nil:NilClass):
app/controllers/pins_controller.rb:23:in `create'

我进行了大量研究，但无法找出问题所在。我是 Rails 的初学者，我正在通过制作一个类似于 pinterest 的网络应用程序来学习它，我可以在其中允许用户创建帐户和发布 pin，我正在使用设计来做到这一点。我添加了回形针以便我可以启用图像发布，并添加了 aws-sdk 以便我可以使用 amazon S3 存储照片，因为我的生产环境在 heroku 上，而 heroku 无法存储图像。我将粘贴一些更有用的代码：

Controller(app/controllers/pins_controller.rb)：这是错误日志中提到的控制器文件。错误在第 23 行，就像它在日志上所说的那样。第 23 行是“创建”操作中的一行：if @pin.save

    class PinsController < ApplicationController
  before_action :set_pin, only: [:show, :edit, :update, :destroy]
  before_action :correct_user, only: [:edit, :update, :destroy]
  before_action :authenticate_user!, except: [:index, :show]

  def index
    @pins = Pin.all
  end

  def show
  end

  def new
    @pin = current_user.pins.build
  end

  def edit
  end

  def create
    @pin = current_user.pins.build(pin_params)

    if @pin.save

      redirect_to @pin, notice: 'Pin was successfully added.'
    else
      render :new
    end
  end

  def update
    if @pin.update(pin_params)
      redirect_to @pin, notice: 'Pin was successfully edited.'
    else
      render :edit
    end
  end

  def destroy
    @pin.destroy
    redirect_to pins_url, notice: 'Pin was successfully deleted.'
  end

  private
    def set_pin
      @pin = Pin.find(params[:id])
    end

    def correct_user
      @pin = current_user.pins.find_by(id: params[:id])
      redirect_to pins_path, notice: "You are not permitted to edit this pin" if @pin.nil?
    end

    def pin_params
      params.require(:pin).permit(:description, :image)
    end
end

模型(app/models/pin.rb)：这是引脚的模型（基本上是帖子）

    class Pin < ActiveRecord::Base
        belongs_to :user

        has_attached_file :image, styles: { medium: "300x300>", thumb: "100x100>" }
        validates_attachment_content_type :image, content_type: /\Aimage\/.*\Z/
    end

配置(config/environments/production.rb)：这是我添加aws配置变量的生产文件

Rails.application.configure do
  # Settings specified here will take precedence over those in config/application.rb.

  # Code is not reloaded between requests.
  config.cache_classes = true

  # Eager load code on boot. This eager loads most of Rails and
  # your application in memory, allowing both threaded web servers
  # and those relying on copy on write to perform better.
  # Rake tasks automatically ignore this option for performance.
  config.eager_load = true

  # Full error reports are disabled and caching is turned on.
  config.consider_all_requests_local       = false
  config.action_controller.perform_caching = true

  # Enable Rack::Cache to put a simple HTTP cache in front of your application
  # Add `rack-cache` to your Gemfile before enabling this.
  # For large-scale production use, consider using a caching reverse proxy like
  # NGINX, varnish or squid.
  # config.action_dispatch.rack_cache = true

  # Disable serving static files from the `/public` folder by default since
  # Apache or NGINX already handles this.
  config.serve_static_files = ENV['RAILS_SERVE_STATIC_FILES'].present?

  # Compress JavaScripts and CSS.
  config.assets.js_compressor = :uglifier
  # config.assets.css_compressor = :sass

  # Do not fallback to assets pipeline if a precompiled asset is missed.
  config.assets.compile = false

  # Asset digests allow you to set far-future HTTP expiration dates on all assets,
  # yet still be able to expire them through the digest params.
  config.assets.digest = true

  # `config.assets.precompile` and `config.assets.version` have moved to config/initializers/assets.rb

  # Specifies the header that your server uses for sending files.
  # config.action_dispatch.x_sendfile_header = 'X-Sendfile' # for Apache
  # config.action_dispatch.x_sendfile_header = 'X-Accel-Redirect' # for NGINX

  # Force all access to the app over SSL, use Strict-Transport-Security, and use secure cookies.
  # config.force_ssl = true

  # Use the lowest log level to ensure availability of diagnostic information
  # when problems arise.
  config.log_level = :debug

  # Prepend all log lines with the following tags.
  # config.log_tags = [ :subdomain, :uuid ]

  # Use a different logger for distributed setups.
  # config.logger = ActiveSupport::TaggedLogging.new(SyslogLogger.new)

  # Use a different cache store in production.
  # config.cache_store = :mem_cache_store

  # Enable serving of images, stylesheets, and JavaScripts from an asset server.
  # config.action_controller.asset_host = 'http://assets.example.com'

  # Ignore bad email addresses and do not raise email delivery errors.
  # Set this to true and configure the email server for immediate delivery to raise delivery errors.
  # config.action_mailer.raise_delivery_errors = false

  # Enable locale fallbacks for I18n (makes lookups for any locale fall back to
  # the I18n.default_locale when a translation cannot be found).
  config.i18n.fallbacks = true

  # Send deprecation notices to registered listeners.
  config.active_support.deprecation = :notify

  # Use default logging formatter so that PID and timestamp are not suppressed.
  config.log_formatter = ::Logger::Formatter.new

  # Do not dump schema after migrations.
  config.active_record.dump_schema_after_migration = false

  config.paperclip_defaults = {
  :storage => :s3,
  :s3_credentials => {
    :bucket => ENV['S3_BUCKET_NAME'],
    :access_key_id => ENV['AWS_ACCESS_KEY_ID'],
    :secret_access_key => ENV['AWS_SECRET_ACCESS_KEY']
  }
}
end

表单(app/views/pins/_form.html.erb)：这是用来提交pins的表单

<%= form_for @pin, html: { multipart: true } do |f| %>
  <% if @pin.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@pin.errors.count, "error") %> prohibited this pin from being saved:</h2>

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

  <div class="form-group">
    <%= f.label :image %><br>
    <%= f.file_field :image, class: "form-control" %>
  </div>

  <div class="form-group">
    <%= f.label :description %><br>
    <%= f.text_field :description, class: "form-control" %>
  </div>
  <div class="form-group">
    <%= f.submit class: "btn btn-primary" %>
  </div>
<% end %>

迁移(db/migrate/20150902154233_add_attachment_image_to_pins.rb)：这是我所做的迁移，以便我可以将照片附加到我的图钉上

class AddAttachmentImageToPins < ActiveRecord::Migration
  def self.up
    change_table :pins do |t|
      t.attachment :image
    end
  end

  def self.down
    remove_attachment :pins, :image
  end
end

Gemfile：这是我的 gemfile，我使用的是 rails4、回形针 4.3 和 aws-sdk 1.6.5

source 'https://rubygems.org'
ruby '2.2.1'

gem 'rails', '4.2.4'

gem 'sass-rails', '~> 5.0'

gem 'uglifier', '>= 1.3.0'

gem 'coffee-rails', '~> 4.1.0'

gem 'jquery-rails'

gem 'turbolinks'

gem 'sdoc', '~> 0.4.0', group: :doc

gem 'bootstrap-sass', '~> 3.3.5' 

gem 'devise', '~> 3.5.2'

gem "paperclip", "~> 4.3"

gem 'aws-sdk', '< 2.0'


group :development, :test do
  # Call 'byebug' anywhere in the code to stop execution and get a debugger console
  gem 'byebug'

  gem 'sqlite3'
end

group :production do
    gem 'pg'
    gem 'rails_12factor'
end

group :development do
  # Access an IRB console on exception pages or by using <%= console %> in views
  gem 'web-console', '~> 2.0'

  # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
  gem 'spring'
end

我现在真的被困住了，我不知道该怎么办。我希望有人能帮帮忙。如果有什么我忘记补充的，请告诉我，我会补充的。

Answer 1

我想通了

在尝试了不同的事情后，我成功了。看看评论看看我做了什么。