Patterns for standalone data fetching subscriptions in re-frame

header.clj

(require '[re-frame.core :as re-frame])
(require '[reagent.ratom :as reagent])
(require '[re-graph.core :as re-graph])
(require '[martian.re-frame :as martian])

;; handler for storing things when they arrive
(re-frame/reg-event-db
 ::on-things
 (fn [db [_ things]]
   (assoc db ::raw-things things)))

martian.clj

;; a standalone subscription that manages polling of an http endpoint every 30 seconds
(re-frame/reg-sub-raw
 ::raw-things
 (fn [db _]
   (let [polling-interval (* 30 1000)
         do-fetch #(re-frame/dispatch [::martian/request :raw-things {} ::on-things])
         ;; request the data from the server every 30 seconds
         poller (js/setInterval do-fetch polling-interval)]

     ;; if the data is not present right now then fetch it immediately
     (when-not (contains? @db ::raw-things)
       (do-fetch))

     ;; return a reaction on the fetched data
     (reagent/make-reaction
      (fn []
        (::raw-things @db))
      ;; when this re-frame subscription is no longer used, stop the poller
      ;; and clean up the database too
      :on-dispose (fn []
                    (js/clearInterval poller)
                    (swap! db dissoc ::raw-things))))))

re-graph.clj

;; a standalone subscription that manages the lifecycle of its upstream data source (re-graph)
(re-frame/reg-sub-raw
 ::raw-things
 (fn [db _]
   ;; when the required data is not present start a re-graph subscription to populate it
   (when-not (contains? @db ::raw-things)
     (re-frame/dispatch [::re-graph/subscribe ::raw-things "{ things { id } }" {} [::on-things]]))

   ;; return a reaction on the subscription response data
   (reagent/make-reaction
    (fn []
      (::raw-things @db))
    ;; when this re-frame subscription is no longer used, clean up the re-graph subscription
    ;; and clean up the database too
    :on-dispose (fn []
                  (re-frame/dispatch [::re-graph/unsubscribe ::raw-things])
                  (swap! db dissoc ::raw-things)))))