Tables in DataMapper w/ Rails not Inheriting Correctly - ruby-on-rails

Question

I'm using DataMapper in Rails, replacing ActiveRecord and am trying to do some single table inheritance. The problem is, sqlite3 seems to be reading all of my inherited tables weird, and so I get some strange errors when trying to create an instance of that table in ruby.
I am using a model, ServerFile, to represent any uploaded or generic file that I want instanced in my database. I have another model, Upload, that extends that and represents an Upload from a user. I have two more models extending from ServerFile, Thumbnail, and UploadThumbnail, to represent a generic Thumbnail and a Thumbnail for an upload accordingly.
The error I keep getting is DataObjects::IntegrityError (server_files.upload_id may not be NULL) when I try to create an instance of an Upload like this:
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
And here are my models:
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
And here is my sqlite schema for the table 'server_files' (and btw, when I list my tables, 'uploads' isn't listed among them):
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

There is no need for an upload_id column on the server_files table. Because Upload inherits from ServerFile, this would essentially be self-referential. The column type with type Discriminator will be set to Upload in the database when the model is successfully saved. That being said, if you want to set a custom upload_id anyways, you can do it with a callback like this:
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
Otherwise, simply write a migration that removes the upload_id column from the server_files table
Source: http://datamapper.org/docs/misc.html

Answer 2

DataMapper for some reason just didn't like my superclass ServerFile. When I broke it up, it worked perfectly! (:
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