Question

我有以下代码：

class User < ActiveRecord::Base
  has_one :profile_image, :as => :owner, :class_name => 'Image'
  has_one :cover_image,   :as => :owner, :class_name => 'Image'
end

和

class Image < ActiveRecord::Base
  belongs_to :owner, polymorphic: true
end

现在我正在尝试构建一个用户可以更新他/她的图像和他/她的电子邮件的表单。我正在构建这样的表单：

= form_for @user, :url => pages_upload_path, :html => { :multipart => true } do |form|
  = form.text_field :email
  = form.fields_for :profile_image_attributes do |profile_image|
    = profile_image.file_field :file
  = form.fields_for :cover_image_attributes do |cover_image|
    = cover_image.file_field :file
  = submit_tag("Upload")

然而，编译为以下参数哈希：

[2] pry(#<PagesController>)> params[:user]
=> {"email"=>"kasper@example.com",
 "profile_image"=>
  {"file"=>
    #<ActionDispatch::Http::UploadedFile:0x007f8a41365d30
     @content_type="image/png",
     @headers=
      "Content-Disposition: form-data; name=\"user[profile_image][file]\"; filename=\"Screenshot 2014-04-27 02.57.34.png\"\r\nContent-Type: image/png\r\n",
     @original_filename="Screenshot 2014-04-27 02.57.34.png",
     @tempfile=
      #<File:/var/folders/_2/rgn574910638hqstf85233hh0000gn/T/RackMultipart20140518-88429-15129ld>>},
 "cover_image"=>
  {"file"=>
    #<ActionDispatch::Http::UploadedFile:0x007f8a413653d0
     @content_type="image/png",
     @headers=
      "Content-Disposition: form-data; name=\"user[cover_image][file]\"; filename=\"Screenshot 2014-04-27 02.57.34.png\"\r\nContent-Type: image/png\r\n",
     @original_filename="Screenshot 2014-04-27 02.57.34.png",
     @tempfile=
      #<File:/var/folders/_2/rgn574910638hqstf85233hh0000gn/T/RackMultipart20140518-88429-1oosnc5>>}}

但是当我保存这个时，我得到以下错误：

@user = User.last
@user.update_attributes(params.fetch(:user, {}).permit(:email, :profile_image => [:file]))
# ActiveRecord::AssociationTypeMismatch: Image(#70115863220300) expected, got    
# ActionController::Parameters(#70115879244320)
# from /Users/kaspergrubbe/.rbenv/versions/2.0.0-p353/lib/ruby/gems/2.0.0/gems
# /activerecord-4.1.0/lib/active_record/associations/association.rb:216:in
# `raise_on_type_mismatch!'

如何让它接受我profile_image的属性？

Answer 1

您需要添加：

accepts_nested_attributes_for :profile_image
accepts_nested_attributes_for :cover_image

您获得的错误是rails分配属性的方式的结果。对于每个键，它调用#{key}=方法，因此在您的情况下，它会尝试将哈希值分配给profile_image。

当您添加accepts_nested_attributes_for时，很多事情都会发生变化。首先，它将定义profile_image_attributes=方法，该方法需要Hash对象，该对象将用于构建或更新关联对象。当fields_for注意到此方法已定义时，它会更新字段的名称以在结尾处包含_attributes，因此一切都会有效。

但请注意，如果没有关联对象，则不会构建fields_for，因此您需要在新的和编辑操作中构建这些对象。

Rails多态嵌套属性，fields_for无法保存

1 个答案: