a_trackers.cljs

(ns app.a-trackers
  (:require [reagent.core :as r]))

(defonce reg-trackers (atom {}))

(defn reg-tracker
  ([k signal]
   (reg-tracker k signal #(rf/dispatch [k %])))
  ([k signal effect]
   (when-let [{:keys [tracker]} (get @reg-trackers k)]
     (r/dispose! tracker))
   (let [signal (r/track #(signal @re-frame.db/app-db))
         tracker (r/track! #(when-let [data @signal] (effect data)))]
     (swap! reg-trackers assoc k {:signal signal :tracker tracker}))))

(defn clear-trackers! []
  (doseq [[k {:keys [tracker]}] @reg-trackers]
    (r/dispose! tracker))
  (reset! reg-trackers {}))

(defn sample-tracker [k]
  (let [{:keys [signal]} (get @reg-trackers k)]
    @signal))

b_example.cljs

(ns b-example)

(defn load-species-args [db]
  (let [region_id (get-in db [:app/state :region :pk])
        category_id (get-in db [:app/state :category :id])]
    (when (and region_id category_id)
      [region_id category_id])))

(reg-event-fx
  :app/load-species
  (fn [_ [_ args]]
    {:sqlite/execute-sql {:query  (str " SELECT * FROM SPECIES "
                                       " WHERE ID IN (SELECT SPECIES_ID FROM SPECIES_REGION WHERE REGION_ID=?) "
                                       "   AND ID IN (SELECT SPECIES_ID FROM SPECIES_CATEGORY WHERE CATEGORY_ID=?) "
                                       " ORDER BY COMMON_NAME")
                          :args   args
                          :resp-v [:app/load-species.resp]}}))

(reg-tracker :app/load-species load-species-args)