assignment.rb

class Assignment < ActiveRecord:Base
  # code omitted

  def set_tasks_from_list(task_attributes)
    self.tasks = self.tasks.new(task_attributes)
  end

  def set_collaborators_from_list(collaborator_ids)
    collaborators = collaborator_ids.map { |id| { collaborator_id: id } }
    self.collaborations = self.collaborations.new(collaborators)
  end

  def assign(assignee_ids)
    assignees = assignee_ids.map { |id| { assignee_id: id } }
    self.assigned_works = self.assigned_works.new(assignees)
  end
end