Ruby on rails 3 在嵌套模型窗体中显示错误消息时出现问题

我很难弄清楚如何显示错误消息——事实上，甚至无法在错误页面上显示页面

以下是我目前拥有的：

media.rb

class Media < ActiveRecord::Base

  belongs_to :project
  has_attached_file :media_file, :default_url => '/media_file/missing.png'

  validates :description, :presence => true
  validates_attachment_content_type :media_file, :content_type => ['image/gif', 'image/jpg', 'image/jpeg', 'image/png', 'audio/mpeg', 'audio/wav']

  MEDIA_TYPES = ["Image", "Audio", "Video"]
end

medias_controller.rb

def new
  @project = Project.find params[:project_id]
  @media = Media.new(:project=>@project)

  respond_to do |format|
    format.html # new.html.erb
    format.xml  { render :xml => @media }
  end
end

def create
  @media = Media.new(params[:media])

  @media.project_id = params[:project_id]

  respond_to do |format|
    if @media.save
      format.html { redirect_to(@media.project, :notice => 'Media was successfully created.') }
      format.xml  { render :xml => @media, :status => :created, :location => @media }
    else
      format.html { render :action => "new" }
      format.xml  { render :xml => @media.errors, :status => :unprocessable_entity }
    end
  end
end

def update
  @media = Media.find(params[:id])

  respond_to do |format|
    if @media.update_attributes(params[:media])
      format.html { redirect_to(@media.project, :notice => 'Media was successfully updated.') }
      format.xml  { head :ok }
    else
      format.html { render :action => "edit" }
      format.xml  { render :xml => @media.errors, :status => :unprocessable_entity }
    end
  end
end

当前的问题是，在尝试为存在验证问题的项目创建新媒体记录时，我遇到以下错误：

---

ActionController:：媒体中的路由错误#创建 显示D:/test/app/views/medias/new.html.erb，其中第5行出现：

没有路由匹配{:action=>“destroy”，:controller=>“projects”}

提取的源（第5行附近）： 2: 三： 4: 5:

---

此错误的url为：（新页面的url为）。如果没有任何验证问题，“创建”将通过。我能够“编辑”现有记录而不会出现问题，这包括在需要时显示验证错误-但是“编辑”验证仅在我将“：update”添加到resources:media和嵌套在：projects中的resources:media之后发生。我不确定这是不是个好主意

非常感谢您对如何实现这一目标的任何见解

resources :medias, :only => [:destroy, :update]
resources :projects do
  resources :medias, :only => [:create, :edit, :index, :new, :show, :update]
end

def new
  @project = Project.find params[:project_id]
  @media = Media.new(:project=>@project)

  respond_to do |format|
    format.html # new.html.erb
    format.xml  { render :xml => @media }
  end
end

def create
  @media = Media.new(params[:media])

  @media.project_id = params[:project_id]

  respond_to do |format|
    if @media.save
      format.html { redirect_to(@media.project, :notice => 'Media was successfully created.') }
      format.xml  { render :xml => @media, :status => :created, :location => @media }
    else
      format.html { render :action => "new" }
      format.xml  { render :xml => @media.errors, :status => :unprocessable_entity }
    end
  end
end

def update
  @media = Media.find(params[:id])

  respond_to do |format|
    if @media.update_attributes(params[:media])
      format.html { redirect_to(@media.project, :notice => 'Media was successfully updated.') }
      format.xml  { head :ok }
    else
      format.html { render :action => "edit" }
      format.xml  { render :xml => @media.errors, :status => :unprocessable_entity }
    end
  end
end