Question

I have

class Question < ActiveRecord::Base
   has_many :tasks, :as => :task
end

class QuestionPlayer < Question
end

class QuestionGame < Question
end

class Tast < ActiveRecord::Base
  belongs_to :task, :polymorphic => true
end

when I do

Task.create :task => QuestionPlayer.new
#<Task id: 81, ... task_id: 92, task_type: "Question">

why? How can I get Task with task_type = “QuestionPlayer” ?

Answer 1

The reason is that you are not actually using polymorphism, you are using STI (Single Table Inheritance). You are defining and setting up both, but only using STI.

The purpose of the foreign key, even a polymorphic foreign key, as you defined it, is to reference another record in a table in the database. Active record must store the primary key and the class which has the table name for the record. This is exactly what it is doing.

Maybe what you really want to do is use STI with different classes for each of your Question objects. In that case, do this,

class CreateQuestionsAndTasks < ActiveRecord::Migration
  def self.up
    create_table :questions do |table|
      table.string :type
    end
    create_table :tasks do |table|
      table.integer :question_id
    end
  end
end
class Question < ActiveRecord::Base
  has_many :tasks
end
class QuestionPlayer < Question
end
class QuestionGame < Question
end
class Task < ActiveRecord::Base
  belongs_to :question
end

Now it will work as you figured.