tracks/db/migrate/019_convert_todo_to_state_machine.rb

class ConvertTodoToStateMachine < ActiveRecord::Migration[5.2]

  class Todo < ActiveRecord::Base; belongs_to :project; end
  class Immediate < Todo; end
  class Deferred < Todo; end
  class Project < ActiveRecord::Base; end

  def self.up
    add_column :todos, :state, :string, :limit => 20, :default => "immediate", :null => false
    @todos = Todo.all
    @todos.each do |todo|
      if todo.done?
        todo.state = 'completed'
      elsif todo.type == 'Deferred'
        todo.state = 'deferred'
      elsif !todo.project.nil? && todo.project.state == 'hidden'
        todo.state = 'project_hidden'
      else
        todo.state = 'active'
      end
      todo.save
    end
    rename_column :todos, 'completed', 'completed_at' #bug in sqlite requires column names as strings
    remove_column :todos, :done
    remove_column :todos, :type
  end

  def self.down
    add_column :todos, :done, :integer, :limit => 4, :default => 0, :null => false
    add_column :todos, :type, :string, :default => "Immediate", :null => false
    rename_column :todos, 'completed_at', 'completed' #bug in sqlite requires column names as strings
    @todos = Todo.all
    @todos.each do |todo|
      todo.done = todo.state == 'completed'
      todo.type = todo.type == 'deferred' ? 'Deferred' : 'Immediate'
      todo.save
    end
    remove_column :todos, :state
  end
end