Controllers (WIP)

https://github.com/metosin/reitit/tree/master/examples/frontend-controllers

Controllers run code when a route is entered and left. This can be useful to:

Load resources
Update application state

Controller is map of:

All properties are optional
:params function, match -> controller parameters
:start & :stop functions

Controllers are defined in route data and as vectors, like:

["/items"
 {:name :items
  :controllers [{:start start-fn, :stop stop-fn)}]}]

To built hierarchies of controllers, nested route data can be used, due to how Reitit merges the route data for nested routes the vectors are concatenated:

["/items"
 {:controllers [{:start start-common-fn}]} ;; A
 [""
  {:name :items
   :controllers [{:start start-items-fn}]}] ;; B
 ["/:id"
  {:name :item
  ;; C
   :controllers [{:params item-param-fn :start start-item-fn}]}]]

In this example both :items and :item routes inherit :controllers from their parent route. Lets call these controllers A, B and C. :items route has controllers A and B and :item A and C.

Controller :start is called when new matches controllers list contains a controller that is not yet initialized. If either of routes is entered from some other route, :start is called for both of routes controllers. If :item is entered from :items only C :start is called, because A controller is identical for both routes. And transition from :item back to :items would only call B :start.

Controller :stop function is called for controllers that were initialized but aren't included in the new match.

To reinitialize a controller when route itself doesn't change, controllers can provide :params function to control their identity based on which parameters they are interested in.

To make C controller depend on routes id path parameter, it should provide following function:

(defn item-param-fn [match]
  (select-keys (:path (:parameters match)) [:id]))

Now, whenever the result value of this function changes, the identity of controller changes and controller is stopped and started.

TODO: Provide way to declare params as data.

Tips

Authentication

Controllers can be used to load resources from a server. If and when your API requires authentication you will need to implement logic to prevent controllers trying to do requests if user isn't authenticated yet.

Run controllers and check authentication

If you have both unauthenticated and authenticated resources, you can run the controllers always and then check the authentication status on controller code, or on the code called from controllers (e.g. re-frame event handler).

Disable controllers until user is authenticated

If all your resources require authentication an easy way to prevent bad requests is to enable controllers only after authentication is done. To do this you can check authentication status and call apply-controllers only after authentication is done (also remember to manually call apply-controllers with current match when authentication is done). Or if no navigation is possible before authentication is done, you can start the router only after authentication is done.

Alternatives

Similar solution could be used to describe required resources as data (maybe even GraphQL query) per route, and then have code automatically load missing resources.

3.4 KiB Raw Blame History