在rails中的图像模型中，Params没有出现错误

Question

我有一个picture模型，它使用carrierwave上传文件。picture模型是user模型和scoreboard模型的多态关系。所有相关代码如下所示。

可显示控制器

class PicturesController < ApplicationController        
  before_filter :load_pictureable
  before_action :logged_in_user, only: [:create, :update, :destroy]

  def create
    @picture = @pictureable.build_picture(picture_params)
    if @picture.save
        flash[:success] = "Uploaded Successfully"
        redirect_to @pictureable
    else
        redirect_to @pictureable
        flash[:danger] = "An error occured, please try again!"
    end
  end

  def update
    @picture = @pictureable.picture
    if @picture.update_attributes(picture_params)
       redirect_to @pictureable
       flash[:success] = "Picture updated successfully"
     else
       redirect_to @pictureable
       flash[:danger] = "An error occured, please try again!"
     end
  end

  def destroy
    @pictureable.picture.delete
    redirect_to @pictureable
    flash[:success] = "Picture removed successfully"
  end

private

  def picture_params
    params.require(:picture).permit(:picture)
  end

  def load_pictureable
    resource, id = request.path.split('/')[1,2]
    @pictureable = resource.singularize.classify.constantize.find(id)
  end
end

我在前端使用HTML5电子阅读器Javascript以一个模式读取图像。文件在模式中显示得很好。Javascript代码如下所示。

$(document).ready(function(){
    var preview = $(".upload-preview img");

    $(".hidden").change(function(event){
       var input = $(event.currentTarget);
       var file = input[0].files[0];
       var reader = new FileReader();
       reader.onload = function(e){
           $('#image')
                    .attr('src', e.target.result)
                    .width(307)
                    .height(317);
           image_base64 = e.target.result;
           preview.attr("src", image_base64);
       };
       reader.readAsDataURL(file);
    });
});

create的动作工作得很完美。但是，当我试图更新一个现有图片时，它是，有时会给我以下错误：param is missing or the value is empty: picture.错误只是偶尔发生。我不太清楚到底发生了什么。我知道错误告诉我picture param不存在。

记录不成功修补程序请求的日志文件。

Started PATCH "/scoreboards/7/pictures/24" for 70.26.106.141 at 2016-05-17 16:27:32 +0000
Processing by PicturesController#update as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"WoA40xzlc8CH6/gcf6Jd/nqlj/9iOoykcn4H9zAgTkuwi6vAttZEPECYs+OfHZvC3le3nY/sZ/IZSwOL0FhnIQ==", "scoreboard_id"=>"7", "id"=>"24"}
  [1m[36mScoreboard Load (0.4ms)[0m  [1mSELECT  "scoreboards".* FROM "scoreboards" WHERE "scoreboards"."id" = $1  ORDER BY "scoreboards"."created_at" DESC LIMIT 1[0m  [["id", 7]]
  [1m[35mUser Load (0.3ms)[0m  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 1]]
  [1m[36mPicture Load (14.4ms)[0m  [1mSELECT  "pictures".* FROM "pictures" WHERE "pictures"."pictureable_id" = $1 AND "pictures"."pictureable_type" = $2 LIMIT 1[0m  [["pictureable_id", 7], ["pictureable_type", "Scoreboard"]]
Completed 400 Bad Request in 24ms

ActionController::ParameterMissing (param is missing or the value is empty: picture):
  app/controllers/pictures_controller.rb:40:in `picture_params'
  app/controllers/pictures_controller.rb:20:in `update'


  Rendered /usr/local/rvm/gems/ruby-2.3.0/gems/web-console-2.0.0.beta3/lib/action_dispatch/templates/rescues/_source.erb (5.0ms)
  Rendered /usr/local/rvm/gems/ruby-2.3.0/gems/web-console-2.0.0.beta3/lib/action_dispatch/templates/rescues/_trace.html.erb (2.3ms)
  Rendered /usr/local/rvm/gems/ruby-2.3.0/gems/web-console-2.0.0.beta3/lib/action_dispatch/templates/rescues/_request_and_response.html.erb (1.5ms)
  Rendered /usr/local/rvm/gems/ruby-2.3.0/gems/web-console-2.0.0.beta3/lib/action_dispatch/templates/rescues/_web_console.html.erb (1.1ms)
  Rendered /usr/local/rvm/gems/ruby-2.3.0/gems/web-console-2.0.0.beta3/lib/action_dispatch/templates/rescues/diagnostics.html.erb within rescues/layout (110.5ms)

成功的POST请求的日志文件

Started POST "/scoreboards/7/pictures" for 70.26.106.141 at 2016-05-17 16:30:00 +0000
Processing by PicturesController#create as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"jNhAeqUJNZGKEGdDCWSGzGRBSwyXkQIj9iZgMMklqBpm09NpDzoCbU1jLLzp20DwwLNzbnpH6XWdE2RMKV2BcA==", "picture"=>{"picture"=>#<ActionDispatch::Http::UploadedFile:0x00000006c6b7d0 @tempfile=#<Tempfile:/tmp/RackMultipart20160517-27824-1d2x6l4.jpeg>, @original_filename="Home_pic.jpeg", @content_type="image/jpeg", @headers="Content-Disposition: form-data; name=\"picture[picture]\"; filename=\"Home_pic.jpeg\"\r\nContent-Type: image/jpeg\r\n">}, "scoreboard_id"=>"7"}
  [1m[35mScoreboard Load (0.4ms)[0m  SELECT  "scoreboards".* FROM "scoreboards" WHERE "scoreboards"."id" = $1  ORDER BY "scoreboards"."created_at" DESC LIMIT 1  [["id", 7]]
  [1m[36mUser Load (0.3ms)[0m  [1mSELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1[0m  [["id", 1]]
  [1m[35mPicture Load (0.5ms)[0m  SELECT  "pictures".* FROM "pictures" WHERE "pictures"."pictureable_id" = $1 AND "pictures"."pictureable_type" = $2 LIMIT 1  [["pictureable_id", 7], ["pictureable_type", "Scoreboard"]]
  [1m[36m (0.2ms)[0m  [1mBEGIN[0m
  [1m[35mSQL (0.7ms)[0m  INSERT INTO "pictures" ("picture", "pictureable_id", "pictureable_type", "created_at", "updated_at") VALUES ($1, $2, $3, $4, $5) RETURNING "id"  [["picture", "Home_pic.jpeg"], ["pictureable_id", 7], ["pictureable_type", "Scoreboard"], ["created_at", "2016-05-17 16:30:03.046590"], ["updated_at", "2016-05-17 16:30:03.046590"]]
  [1m[36m (29.2ms)[0m  [1mCOMMIT[0m
Redirected to https://scorecliq-kpauls.c9users.io/scoreboards/7
Completed 302 Found in 2253ms (ActiveRecord: 31.2ms)

视图文件在模式中被处理。代码如下所示。editphoto模式和upload photo模式是相同的。下面的是EDITPHOTO模式/上传照片.

<div>
  <%= form_for([@pictureable, @picture], html: {multipart: true}) do |f| %>
   <%= f.file_field :picture, accept: 'image/jpeg,image/gif,image/png', id: "files", class: "hidden" %>

     <div class="modal fade" id="picmodal" tabindex="-1" role="dialog" aria-labelledby="picmodal" aria-hidden="true"> 
        <div class="modal-dialog">
          <div class="modal-content">
            <div class="modal-header" style="text-align: center">Selected Image</div>
             <div class="modal-body">
             <div class="upload-preview" style="text-align: center">
               <img id="image" /></img>
             </div>
            </div>
            <div class="modal-footer">
                <%= f.submit "upload photo", class: "hidden", id: "editphotobutton" %>
                <button class="btn-s btn-full", for: "editphotobutton">Save Changes</button>
                <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
            </div>
          </div>
        </div>
      </div>
  <% end %>
</div>

单击选项以更改图片的视图代码

   <div class="col-xs-12 col-sm-3 score-prof-pic">
         <% if @picture.picture.url.present? %>
            <div class="dropdown">
               <%= link_to "#", class: "prof-dropdown" , data: {:toggle => "dropdown"}, role: "button", aria: {:expanded => "false"} do %>
                   <%= image_tag @picture.picture.url, class: "prof-default img-thumbnail" %>
               <% end %>
               <% if manager_or_owner?(@scoreboard, current_user) %>
                  <ul class="dropdown-menu">
                     <li><%= link_to "Upload","#", id: "score-prof-edit" %> </li>
                     <li role="separator" class="divider"></li>
                     <li> <%= link_to "Remove", [@pictureable, @picture], method: :delete, data: {confirm: "Are you sure you want to delete your picture!"} %></li>
                     <li role="separator" class="divider"></li>
                     <li><%= link_to "Cancel", "#" %></li>
                  </ul>
               <% end %>
            </div>
         <% else %>
            <div class="dropdown">
               <%= link_to "#", class: "prof-dropdown" , data: {:toggle => "dropdown"}, role: "button", aria: {:expanded => "false"} do %>
                   <%= image_tag "blank-prof.jpg", class: "prof-default img-thumbnail " %>
               <% end %>
               <% if manager_or_owner?(@scoreboard, current_user) %>
               <ul class="dropdown-menu">
                  <li><%= link_to "Upload","#", id: "score-prof-upload" %> </li>
                  <li role="separator" class="divider"></li>
                  <li><%= link_to "Cancel", "#" %></li>
               </ul>
               <% end %>
            </div>
         <% end %>
     </div>

Answer 1

控制器的Rails强参数当前要求在用户更新图片模型时上传新图片。这意味着，如果用户提交表单而没有上传新图像，即使他们以前成功地上传了图像，强参数也会导致操作失败。

若要解决此问题，请将picture_params方法更改为：

def picture_params
  params.permit(:picture)
end

这将允许update工作，即使用户没有选择新文件。理想情况下，UI将禁用Save或Submit按钮，直到用户选择要上载的文件，以确保良好的用户体验。

若要验证用户至少上传了一次文件，请向图片模型中添加验证，以验证用户是否存在图片。在不知道字段名的具体细节的情况下，您可以像这样进行验证(假设:image：

def Picture < ActiveRecord::Base
  validate :has_picture

private

  def has_picture
    errors.add(:picture, "can't be missing") if !picture.url.present?
  end
end

这种方法将在节省时间(而不是在调用操作时)为您提供验证。这不仅应使操作更加健壮，而且应确保模型始终有效。