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101 lines
3.4 KiB
Markdown
101 lines
3.4 KiB
Markdown
# Controllers (WIP)
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* https://github.com/metosin/reitit/tree/master/examples/frontend-controllers
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Controllers run code when a route is entered and left. This can be useful to:
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- Load resources
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- Update application state
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Controller is map of:
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- All properties are optional
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- `:params` function, `match` -> controller parameters
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- `:start` & `:stop` functions
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Controllers are defined in [route data](../basics/route_data.md) and
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as vectors, like:
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```
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["/items"
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{:name :items
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:controllers [{:start start-fn, :stop stop-fn)}]}]
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```
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To built hierarchies of controllers, nested route data can be used,
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due to how Reitit merges the route data for nested routes the vectors are
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concatenated:
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```
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["/items"
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{:controllers [{:start start-common-fn}]} ;; A
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[""
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{:name :items
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:controllers [{:start start-items-fn}]}] ;; B
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["/:id"
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{:name :item
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;; C
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:controllers [{:params item-param-fn :start start-item-fn}]}]]
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```
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In this example both `:items` and `:item` routes inherit `:controllers` from
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their parent route. Lets call these controllers A, B and C. `:items` route
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has controllers A and B and `:item` A and C.
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Controller `:start` is called when new matches controllers list contains a
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controller that is not yet initialized. If either of routes is entered
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from some other route, `:start` is called for both of routes controllers.
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If `:item` is entered from `:items` only C `:start` is called, because
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A controller is identical for both routes. And transition from `:item`
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back to `:items` would only call B `:start`.
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Controller `:stop` function is called for controllers that were
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initialized but aren't included in the new match.
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To reinitialize a controller when route itself doesn't change,
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controllers can provide `:params` function to control their
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identity based on which parameters they are interested in.
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To make C controller depend on routes `id` path parameter, it should
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provide following function:
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```clj
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(defn item-param-fn [match]
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(select-keys (:path (:parameters match)) [:id]))
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```
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Now, whenever the result value of this function changes, the identity
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of controller changes and controller is stopped and started.
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TODO: Provide way to declare params as data.
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## Tips
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### Authentication
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Controllers can be used to load resources from a server. If and when your
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API requires authentication you will need to implement logic to prevent controllers
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trying to do requests if user isn't authenticated yet.
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#### Run controllers and check authentication
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If you have both unauthenticated and authenticated resources, you can
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run the controllers always and then check the authentication status
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on controller code, or on the code called from controllers (e.g. re-frame event
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handler).
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#### Disable controllers until user is authenticated
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If all your resources require authentication an easy way to prevent bad
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requests is to enable controllers only after authentication is done.
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To do this you can check authentication status and call `apply-controllers`
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only after authentication is done (also remember to manually call `apply-controllers`
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with current `match` when authentication is done). Or if no navigation is possible
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before authentication is done, you can start the router only after
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authentication is done.
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## Alternatives
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Similar solution could be used to describe required resources as data (maybe
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even GraphQL query) per route, and then have code automatically load
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missing resources.
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