Controllers and Action Composition

There are quite a number of entity types in use in the EHRI portal and most of their behaviours with regard to permissions, access control, and the CRUD lifecycle are shared. To greatly reduce code duplication the portal app makes extensive use of Play’s Action Composition mechanism, dividing up these generic behaviours into a set of parameterised traits that can be mixed into controllers to handle operations on a particular type of entity. In addition to just Create, Read, Update, and Delete, we also have generic controller traits for:

  • Setting item-level permissions
  • Setting scoped permissions
  • Setting visibility (access control)
  • Promotion
  • Search
  • Creating child items
  • Managing descriptions

The UserProfile and Group types also share quite a bit of behaviour since they can both be added to other groups and be assigned global permissions to manage entire item types; these are also implemented via generic controller traits.

In general, generic actions consist of two parts:

  1. rendering a form
  2. validating the form data, and either: - re-rendering the form with errors - acting on the form data

In general we don’t do any actual rendering since the specific data rendered will depend on the item type; this part is left to the concrete controller implementation.

In both cases we also need to validate that the user performing the action has permission to do it. This happens a lot, so most of the generic controllers themselves compose an ActionBuilder called :scala:`WithContentPermissionAction(permissionType, contentType)` that either allows to action to proceed or renders a 403 Forbidden response.

Simplified Example

A simplified example of this system is shown below; it handles one particular action (setting item visibility) for the Country data type:

case class Countries @Inject()(
  controllerComponents: ControllerComponents,
  appComponents: AppComponents
) extends AdminController with Visibility[Country] {

  def get(id: String: Action[AnyContent] = ??? // Stubbed for this example...

  def visibility(id: String): Action[AnyContent] = EditVisibilityAction(id).apply { implicit request =>
      request.users, request.groups, countryRoutes.visibilityPost(id)))

  def visibilityPost(id: String): Action[AnyContent] = UpdateVisibilityAction(id).apply { implicit request =>
      .flashing("success" -> "item.update.confirmation")

This (simplified) controller mixes in the Visibility[T] trait, parameterised by the Country model. The trait provides two composable actions: EditVisibilityAction and UpdateVisibilityAction:

This checks for the user’s permission to update the item’s visibility and, if they are allowed, runs a function taking a VisibilityRequest (which contains the item in question and other contextual info such as a list of possible users and groups to grant access) and returning a response. In our example controller this renders a form with a 200 response, pre-filling the form with the IDs of the users and groups who can currently access the item.
This also checks for the user’s permission to update the item’s visibility and, if allowed, sets it from the form data and runs an action taking another request and returning a response. In our example this simply redirects to the item’s detail page.

Most of the generic controller have similar New/Create, Edit/Update pairs which map to a doThing/doThingPost actions. Some are more complicated in that they return a request which contains either a form of some type (if the form was invalid) or a new or updated item. For example, the CreateItemAction action builder users a CreateRequest[A], which is a wrapped request which, simplified slightly, looks like:

case class CreateRequest[A](
  formOrItem: Either[Form[F],MT],
  user: UserProfile,
  request: Request[A]
) extends WrappedRequest[A](request)

That is, the caller receives a request containing either a Form[F] (where F is the type of the item’s data) or an item of type MT so they can either render the form again or do something with the newly-created item.