Question

我在Rails中使用DataMapper，替换ActiveRecord并尝试进行单表继承。问题是，sqlite3似乎正在读取我所有的继承表，因此在尝试在ruby中创建该表的实例时会出现一些奇怪的错误。

我正在使用模型ServerFile来表示我想要在我的数据库中实例化的任何上传或通用文件。我有另一个模型，上传，它扩展了它并代表用户的上传。我还有两个模型，从ServerFile，Thumbnail和UploadThumbnail延伸，代表相应的上传缩略图和缩略图。

当我尝试创建一个像这样的上传实例时，我一直得到的错误是DataObjects::IntegrityError (server_files.upload_id may not be NULL)：

upload = Upload.new(
    filename: uploaded_io.original_filename, 
    path: path.to_s, 
    content_type: uploaded_io.content_type, 
    token: rand_token())

upload.member = @member
upload.title = params[:title]
upload.description = params[:description]
upload.save

这是我的模特：

class ServerFile
    include DataMapper::Resource
    property :id, Serial
    property :token, String, unique_index: true
    property :filename, String
    property :path, Text, unique: true
    property :content_type, Text, length: 5..200
    property :type, Discriminator

    property :created_on, Date
    property :created_at, DateTime
    property :updated_on, Date
    property :updated_at, DateTime
end

class Upload < ServerFile
    property :title, String
    property :description, Text

    has n, :topics, through: Resource
    has n, :subjects, through: Resource
    has n, :downloads
    has n, :comments, 'UploadComment'
    has n, :ratings, 'UploadRating'

    belongs_to :member
    has 1, :thumbnail, 'UploadThumbnail', required: false
end

class Thumbnail < ServerFile
    @@IMAGE_EXTENSIONS = [:'png', :'jpg', :'jpeg', :'gif', :'svg', :'cgm']
    validates_with_method :filename, :is_valid_image?

    def is_valid_image?
        @@IMAGE_EXTENSIONS.each do |ext|
            return true if /[\w\d\.\_\-]+\.#{ext.to_s}/ =~ @filename
        end
        [false, 'Invalide image type.']
    end
end

class UploadThumbnail < Thumbnail
    belongs_to :upload
end

这是我的表的sqlite架构＆＃39; server_files＆＃39; （顺便说一句，当我列出我的表格时，＆＃39;上传内容并未列在其中）：

sqlite> .schema server_files
CREATE TABLE "server_files" ("id" INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, "token" VARCHAR(50), "filename" VARCHAR(50), "path" TEXT, "content_type" TEXT, "type" VARCHAR NOT NULL, "created_on" DATE, "created_at" TIMESTAMP, "updated_on" DATE, "updated_at" TIMESTAMP, "title" VARCHAR(50), "description" TEXT, "member_id" INTEGER NOT NULL, "upload_id" INTEGER NOT NULL);
CREATE UNIQUE INDEX "unique_server_files_path" ON "server_files" ("path");
CREATE UNIQUE INDEX "unique_server_files_token" ON "server_files" ("token");

Answer 1

upload_id表上不需要server_files列。因为Upload继承自ServerFile，所以这基本上是自我指涉的。模型成功保存后，类型为type的列Discriminator将在数据库中设置为Upload。话虽这么说，如果你想设置一个自定义的upload_id，你可以用这样的回调来做：

before :create, :generate_upload_id

def generate_upload_id
  generated_upload_id = <do something>
  attribute_set(:upload_id, generated_upload_id) unless upload_id
end

否则，只需编写一个从server_files表中删除upload_id列的迁移

来源：http://datamapper.org/docs/misc.html

Answer 2

DataMapper出于某种原因只是不喜欢我的超类ServerFile。当我把它分解时，它完美无缺！（：

class Upload < ServerFile
    include DataMapper::Resource
    property :id, Serial
    property :token, String, unique_index: true
    property :filename, String
    property :path, Text, unique: true
    property :content_type, Text, length: 5..200

    property :created_on, Date
    property :created_at, DateTime
    property :updated_on, Date
    property :updated_at, DateTime
    property :title, String
    property :description, Text

    has n, :topics, through: Resource
    has n, :subjects, through: Resource
    has n, :downloads
    has n, :comments, 'UploadComment'
    has n, :ratings, 'UploadRating'

    belongs_to :member
    has 1, :thumbnail, 'UploadThumbnail', required: false
end

class Thumbnail < ServerFile
    include DataMapper::Resource
    property :id, Serial
    property :token, String, unique_index: true
    property :filename, String
    property :path, Text, unique: true
    property :content_type, Text, length: 5..200
    property :type, Discriminator

    property :created_on, Date
    property :created_at, DateTime
    property :updated_on, Date
    property :updated_at, DateTime

    @@IMAGE_EXTENSIONS = [:'png', :'jpg', :'jpeg', :'gif', :'svg', :'cgm']
    validates_with_method :filename, :is_valid_image?

    def is_valid_image?
        @@IMAGE_EXTENSIONS.each do |ext|
            return true if /[\w\d\.\_\-]+\.#{ext.to_s}/ =~ @filename
        end
        [false, 'Invalide image type.']
    end
end

class UploadThumbnail < Thumbnail
    belongs_to :upload
end

DataMapper中的表没有Rails无法正确继承

2 个答案: