title: handling order with has_many through relationship
body: <p>I have two models: project and task (for example) with a join model: project_task enabling a has_many through relationship so that tasks may be shared across projects.</p>
  
  <p>I have specified position as an attribute of the project_task model. Now I want to be able to access tasks by their position in the project_tasks table via a given project.</p>
  
  <p>i.e. project.tasks (ordered by the position listed for each task in the project_tasks table).</p>
  
  <p>Is this possible?</p>