foo.clj

(def conn (d/create-conn {}))

(d/transact! conn
             [{:db/id -1
               :app/counter? true
               :app/count-main 3
               :app/count-sub 6}])

(defmulti read om/dispatch)

(defmethod read :app/counter
  [{:keys [state query]} _ _]
  (println "Fetching app/counter..." state query)
  {:value (d/q '[:find [(pull ?e ?selector) ...]
                 :in $ ?selector
                 :where [?e :app/counter?]]
               (d/db state) query)})

(defmulti mutate om/dispatch)

(defui Sub
  static om/IQuery
  (query [this]
         [{:app/counter [:db/id :app/count-sub]}])
  Object
  (render [this]
          (println "Sub props:" (om/props this))
          (let [{:keys [app/title app/count-sub] :as entity}
                (get-in (om/props this) [:app/counter 0])]
            (dom/p nil (str "Sub Count: " count-sub)))))

(def other-ui (om/factory Sub))

(def reconciler (om/reconciler
                 {:state conn
                  :parser (om/parser {:read read :mutate mutate})}))

(defui Main
  static om/IQuery
  (query [this]
         [{:app/counter [:db/id :app/count-main]}])
  Object
  (render [this]
          (println "Main props:" (om/props this))
          (dom/div nil
                   (let [{:keys [app/title app/count-main] :as entity}
                         (get-in (om/props this) [:app/counter 0])]
                     (dom/p nil (str "Main Count: " count-main)))
                   (other-ui))))

(if-let [node (gdom/getElement "app")]
  (om/add-root! reconciler Main node))

Main Count: 3

Sub Count:

Fetching app/counter... #object [cljs.core.Atom {:val #datascript/DB {:schema {}, :datoms [[1 :app/count-main 3 536870913] [1 :app/count-sub 6 536870913] [1 :app/counter? true 536870913]]}}] [:db/id :app/count-main]
Main props: {:app/counter [{:db/id 1, :app/count-main 3}]}
Sub props: nil
Fetching app/counter... #object [cljs.core.Atom {:val #datascript/DB {:schema {}, :datoms [[1 :app/count-main 3 536870913] [1 :app/count-sub 6 536870913] [1 :app/counter? true 536870913]]}}] [:db/id :app/count-main]