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我正在使用carrierwave 和Jcrop 裁剪图像。保存图像的模型被调用Item，存储图像的字段被调用cover。

种植工作进展顺利。问题与为项目投票的 ajax 动作有关。

每个项目都有一个名为 的字段votes。我在项目顶部有一个按钮，单击该按钮时会votes按增量将值加 1。如果我不使用 ajax 操作，它会正确更新记录，不会造成任何伤害。但是，如果我使用 ajax 操作，它会使用新属性更新 Item 记录中的所有字段，这些属性将裁剪图像的尺寸更改为几乎为零，然后触发 after_update 回调来重新处理图像。

结果是我得到了一个 1px x 1px 并且完全白色的图像。

如何将我的 ajax 操作更改为不发生这种情况？

谢谢

  def vote
    item = Item.find(params[:item_id])
    item.increment!(:votes)

    if request.xhr?
      render json: {votes: item.votes}
    else
      redirect_to users_url
    end
  end

jQuery ($) ->
  $('form.vote').submit (evt) ->
    evt.preventDefault()

    $form = $ @
    $form.find(':submit').prop 'disabled', true
    $.post($form.attr('action'), $form.serializeArray(), type: 'json').done (data) ->
      $form.parent().find(".vote_count").text data.votes

并作为参考项目模型：

class Item < ActiveRecord::Base
  before_create :update_image_attributes
  before_update :reprocess_image, :if => :cropping?

  belongs_to :user

  attr_accessible :available, :cover, :privacy, :size, :title, :votes, :user_id, :description, :crop_x, :crop_y, :crop_w, :crop_h

  mount_uploader :cover, CoverUploader

  def cropping?
    !crop_x.blank? && !crop_y.blank? && !crop_w.blank? && !crop_h.blank?
  end

  private

  def update_image_attributes
    if cover.present?
      self.content_type = cover.file.content_type
      self.file_size = cover.file.size
      self.width, self.height = `identify -format "%wx%h" #{cover.file.path}`.split(/x/)
    end
  end

  def reprocess_image
      cover.reprocess(crop_x, crop_y, crop_w, crop_h)
      cover.cache_stored_file!
  end

end

和控制器

class ItemsController < ApplicationController
      before_filter :authenticate

      def crop
        @item = Item.find(params[:image_id])
        @user = User.find(params[:user_id])
        respond_to do |format|
          if @item.update_attributes(:crop_x => params[:crop_x],:crop_y => params[:crop_y],:crop_w => params[:crop_w],:crop_h => params[:crop_h])
            format.html { redirect_to items_url }
            format.js
          else
            redirect_to root_url
          end
        end
      end

      # GET /items
      # GET /items.json
      def index
        @items = Item.all

        respond_to do |format|
          format.html # index.html.erb
          format.json { render json: @items }
        end
      end

      # GET /items/1
      # GET /items/1.json
      def show
        @item = Item.find(params[:id])

        respond_to do |format|
          format.html # show.html.erb
          format.json { render json: @item }
        end
      end

      # GET /items/new
      # GET /items/new.json
      def new
        @item = Item.new

        respond_to do |format|
          format.html # new.html.erb
          format.json { render json: @item }
        end
      end

      # GET /items/1/edit
      def edit
        @item = Item.find(params[:id])
      end

      # POST /items
      # POST /items.json
      def create
        @item = Item.create(params[:item])
        respond_to do |format|
          if @item.save
            format.html { redirect_to items_url }
            format.js
          else
            format.html { render action: "new" }
            format.json { render json: @item.errors, status: :unprocessable_entity }
          end
        end
      end

      # PUT /items/1
      # PUT /items/1.json
      def update
        @item = Item.find(params[:id])
        respond_to do |format|
          if @item.update_attributes(params[:item])
            format.html { redirect_to @item, notice: 'Item was successfully updated.' }
            format.json { head :no_content }
          else
            format.html { render action: "edit" }
            format.json { render json: @item.errors, status: :unprocessable_entity }
          end
        end
      end

      # DELETE /items/1
      # DELETE /items/1.json
      def destroy
        @item = Item.find(params[:id])
        @item.destroy

        respond_to do |format|
          format.html { redirect_to items_url }
          format.json { head :no_content }
        end
      end

      private

      def authenticate
        if current_user.nil?
          redirect_to root_path, :alert => "You must first log in to access this page"
        end
      end
    end

更新 - 提交日志

Started POST "/vote" for 127.0.0.1 at 2012-08-15 23:28:03 +0200
Processing by VotesController#vote as */*
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"uVxsVGsXImC2VPsavIjZfIUMnGmlyjYEmubI8oODgdk=", "item_id"=>"107", "user_id"=>"1"}
  Category Load (0.2ms)  SELECT "categories".* FROM "categories" 
  Color Load (0.1ms)  SELECT "colors".* FROM "colors" 
  User Load (0.1ms)  SELECT "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", "1"]]
   (0.1ms)  begin transaction
  SQL (9.2ms)  INSERT INTO "votes" ("created_at", "item_id", "updated_at", "user_id") VALUES (?, ?, ?, ?)  [["created_at", Wed, 15 Aug 2012 21:28:03 UTC +00:00], ["item_id", 107], ["updated_at", Wed, 15 Aug 2012 21:28:03 UTC +00:00], ["user_id", 1]]
   (3.1ms)  commit transaction
  Item Load (0.3ms)  SELECT "items".* FROM "items" WHERE "items"."id" = ? LIMIT 1  [["id", 107]]
   (0.0ms)  begin transaction
   (0.4ms)  UPDATE "items" SET "votes" = 1, "updated_at" = '2012-08-15 21:28:03.656131' WHERE "items"."id" = 107
   (23.2ms)  commit transaction
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