Rails 3和carrierwave：无法将nil转换为String答案

【问题标题】：Rails 3 and carrierwave: can't convert nil into StringRails 3和carrierwave：无法将nil转换为String
【发布时间】：2015-06-21 19:07:43
【问题描述】：

我正在尝试在我的 rails 应用程序中使用carrierwave gem 实现上传图像，但是当我按下表单的提交按钮时，我收到以下错误：“无法将 nil 转换为字符串”.

应用程序跟踪：

app/controllers/uploads_controller.rb:48:in `new'
app/controllers/uploads_controller.rb:48:in `create'

请求：

{"utf8"=>"✓",
"authenticity_token"=>"VsgoOE/BQwwT0aQRRMO22kxdPgC/BS2H/CnHVBi4Cfw=",
"upload"=>{"name"=>"aaa",
"description"=>"aa",
"image"=>[#<ActionDispatch::Http::UploadedFile:0x508a8b0 @original_filename="c1147374806dce0ec967015c041fec3b.jpg",
@content_type="image/jpeg",
@headers="Content-Disposition: form-data; name=\"upload[image][]\"; filename=\"c1147374806dce0ec967015c041fec3b.jpg\"\r\nContent-Type: image/jpeg\r\n",
@tempfile=#<File:C:/Users/user/AppData/Local/Temp/RackMultipart20150621-5356-1gm0atx>>]},
"commit"=>"Upload"}

上传模型：

class Upload < ActiveRecord::Base
    validates_presence_of :user_id, :image
    attr_accessible :name, :description, :image
    mount_uploader :image, ImageUploader
end

上传控制器：

class UploadsController < ApplicationController
    before_filter :signed_in_user

    def index
    (...)
    end

    def show
    (...)
    end

    def new
        @upload = Upload.new
        respond_to do |format|
            format.html # new.html.erb
            format.json { render json: @upload }
        end
    end

    def edit
        (...)
    end

    def create
        @upload =  Upload.new(params[:upload])
        @upload.user_id = current_user.id
        respond_to do |format|
            if @upload.save

                format.html { redirect_to @upload, notice: 'Image was uploaded.' }
                format.json { render json: @upload, status: :created, location: @upload }

            else
                format.html { render action: "new" }
                format.json { render json: @upload.errors, status: :unprocessable_entity }
            end
        end
    end

    def update
        (...)
    end

    def destroy
        (...)
    end
end

上传表单（uploads/_form.html.erb）：

<%= form_for @upload, :html => {:id => "upload_form", :multipart => true} do |f| %>
    <div class="field">
        <%= f.text_field :name, placeholder: 'Title' %>
    </div>
    <div class="field">
        <%= f.text_field :description, placeholder: 'Description' %>
    </div>
    <%= f.file_field :image, multiple: true %>
    <div class="actions">
        <%= f.submit "Upload" %>
    </div>
<% end %>

载波上传器：

class ImageUploader < CarrierWave::Uploader::Base
    storage :file

    def store_dir
        "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
    end
end

上传架构：

create_table "uploads", :force => true do |t|
    t.string   "name"
    t.string   "description"
    t.integer  "user_id"
    t.datetime "created_at",  :null => false
    t.datetime "updated_at",  :null => false
    t.string   "image"
end

carrierwave保存图片的目录：

public
    uploads
        upload
            image
                1
                ...

应用程序跟踪引用的第 48 行是 @upload = Upload.new(params[:upload])。

我该如何解决这个问题？我不明白为什么上传是nil。有人可以把我放在正确的位置吗？

一些细节：OS Win7 Pro、Rails v.3.2.21、Carrierwave v.0.10.0、IDE Rubymine v.7.1.2

编辑 1：根据@sreena 的建议，我从上传切换到图片，现在这是请求消息：

Parameters: {"utf8"=>"✓",
"authenticity_token"=>"G1zpdyCbXRJYqAR5m5hscMjQOry85KN7toNhJznOFok=",
"upload"=>{"name"=>"titolo", "description"=>"descrizione",
"image"=>[#<ActionDispatch::Http::UploadedFile:0x534aef0 @original_filename="2.jpg", 
@content_type="image/jpeg", @headers="Content-Disposition: form-data;
name=\"upload[image][]\"; filename=\"2.jpg\"\r\nContent-Type: image/jpeg\r\n",
@tempfile=#<File:C:/Users/user/AppData/Local/Temp/RackMultipart20150624-4180-14oypoq>>]},
"commit"=>"Upload"}

按下提交按钮后，现在我从表单中收到另一个错误提示："Image can't be blank"。

【问题讨论】：

标签： ruby-on-rails carrierwave

【解决方案1】：

这让我觉得你的 routes.rb 文件中有一些无效的内容。

检查版本明智的路由语法和所有...

并检查gem carrierwave 版本...

【讨论】：

【解决方案2】：

你应该像这样在控制器中传递创建参数

@upload = Upload.new(params[:image])

，应该是图片不上传

【讨论】：

我听从了您的建议，但现在我收到一条新的错误消息：“图像不能为空白”（当我按下提交按钮时）。它似乎无法识别图像。编辑中的新请求错误。

【解决方案3】：

在您的 UploadsContoller 页面中添加此功能 def upload_params params.require(:upload).permit(:image,:name,:description) end

然后在 def create 添加这样的

def create @upload = Upload.new(upload_params) @upload.user_id = current_user.id respond_to do |format| if @upload.save

            format.html { redirect_to @upload, notice: 'Image was uploaded.' }
            format.json { render json: @upload, status: :created, location: @upload }

        else
            format.html { render action: "new" }
            format.json { render json: @upload.errors, status: :unprocessable_entity }
        end
    end
end

【讨论】：

抱歉延迟，添加该功能，当我尝试上传图像时，但我收到消息“无法将 nil 转换为字符串”，所以我认为这应该是 gem 版本问题或某物。无论如何感谢您的建议！

【解决方案4】：

最后我解决了这个问题。我只是通过以下方式更改创建方法

def create
    @upload =  current_user.uploads.build(params[:upload])
    @upload.image = params[:upload]["image"]
    respond_to do |format|
    if @upload.save

        format.html { redirect_to @upload, notice: 'Image was uploaded.' }
        format.json { render json: @upload, status: :created, location: @upload }

    else
        format.html { render action: "new" }
        format.json { render json: @upload.errors, status: :unprocessable_entity }
    end
end

【讨论】：