Rails 4多个多态has_one关系不起作用

Question

我正在尝试从我的Booth 模型中使用以下三个多态关联

has_one :uploaded_file, as: :imageable, dependent: :destroy
accepts_nested_attributes_for :uploaded_file

has_one :company_logo, as: :imageable, class_name: 'UploadedFile', dependent: :destroy
accepts_nested_attributes_for :company_logo

has_one :booth_main_image, as: :imageable, class_name: 'UploadedFile', dependent: :destroy
accepts_nested_attributes_for :booth_main_image

但是，这不起作用，当我在该关联的资源上单独使用 build 方法时，我在视图中得到相同的值。

在我的uploaded_files 数据库表中，我有imageable_id 和imageable_type 我想将此用于公司徽标和展位主图像之类的东西，因为否则我必须创建更多列来支持其他多态关联，如果不使用它们将留下null。

下面是UploadedFile的模型：

class UploadedFile < ActiveRecord::Base
    belongs_to :imageable, polymorphic: true

    has_attached_file :assets

    validates_attachment_content_type :assets, 
        :content_type => /^image\/(png|gif|jpeg)/,
        :default_url => "/images/:style/missing.png",
        :message => "only (png|gif|jpeg) images are allowed and the size cannot exceed 5mb",
        :size => { :in => 0..5000.kilobytes }

end

有没有办法为上述所有关联使用一组多态列？

Answer 1

您遇到此问题的原因是因为has_one 将确保目标表中只有一条记录（在您的情况下为uploaded_files）将指向 Booth 模型。如果您想区分同一模型的不同类型，则需要在某处设置一个标志以指示它是哪种类型。

为此，首先您需要添加一个标识图像类型的列：

# in a migration
def change
  add_column :uploaded_files, :image_type, :string
end

您可以将预期的图像类型定义为常量：

class UploadedFile < ActiveRecord::Base
  IMAGE_TYPE_STANDARD = 'Standard'
  IMAGE_TYPE_LOGO     = 'Logo'
  IMAGE_TYPE_BOOTH    = 'Booth'
end

现在您的关联应该反映这些类型：

class Booth < ActiveRecord::Base
  # optional - if you want to access all attached uploads
  has_many :uploaded_files, :as => :imageable, :dependent => :destroy

  has_one  :uploaded_file, :as => :imageable, :dependent => :destroy, 
           conditions: { image_type: UploadedFile::IMAGE_TYPE_STANDARD }
  has_one  :company_logo, :as => :imageable, :class_name => 'UploadedFile', 
           :dependent => :destroy, 
           conditions: { image_type: UploadedFile::IMAGE_TYPE_LOGO }
  has_one  :booth_main_image, :as => :imageable, :class_name => 'UploadedFile', 
           :dependent => :destroy, 
           conditions: { image_type: UploadedFile::IMAGE_TYPE_BOOTH }

  accepts_nested_attributes_for ...
end

请注意，您不必手动设置image_type。由于类型是由条件设置的，ActiveRecord 会在您构建或创建 has_one 关联之一时为您设置它：

upload = @booth.build_uploaded_file(asset: some_asset)
upload.image_type 
=> 'Standard'