significant rework to defvc, simplifying sub/unsubing to views

defvc components no longer declare the view-sigs that will be used.
calls to view-cursor within the component's render function now
automatically trigger the component to subscribe/unsubscribe to the
view-sigs being passed to any view-cursor calls.

src/cljs/reagent_data_views/client/component.clj

@@ -1,26 +1,42 @@
 (ns reagent-data-views.client.component)
 
 (defmacro defvc
-  [component-name args view-sigs & body]
+  "Defines a Reagent component that works the same as any other defined
-  `(defn ~component-name ~args
+   using defn with the addition that view-cursor can be used in the
-     (let [gen-view-sigs#         (fn ~args ~view-sigs)
+   render function of these components to access data from subscribed
-           get-current-view-sigs# (fn [this#]
+   views.
-                                    (apply gen-view-sigs# (rest (reagent.core/argv this#))))]
+
+   To subscribe to a view, simply call view-cursor with the signature of
+   the view you want to subscribe to and read data from. view-cursor and
+   components defined with defvc will automatically manage subscribing
+   and unsubscribing to views as the view signatures passed to any
+   view-cursor calls change across the lifetime of this component."
+  [component-name args & body]
+  `(defn ~component-name []
      (reagent.core/create-class
        {:component-will-mount
         (fn [this#]
-            (let [current-view-sigs# (get-current-view-sigs# this#)]
+          (reagent-data-views.client.component/prepare-for-render! this#))
-              (reagent-data-views.client.component/subscribe! this# current-view-sigs#)))
+
+        :component-did-mount
+        (fn [this#]
+          ; invoked immediately after the initial render has occurred.
+          ; we do this here because component-did-mount does not get called
+          ; after the initial render, but will be after all subsequent renders.
+          (reagent-data-views.client.component/update-subscriptions! this#))
 
         :component-will-unmount
         (fn [this#]
           (reagent-data-views.client.component/unsubscribe-all! this#))
 
+        :component-will-receive-props
+        (fn [this# new-argv#]
+          (reagent-data-views.client.component/prepare-for-render! this#))
+
         :component-did-update
         (fn [this# old-argv#]
-            (let [new-view-sigs# (get-current-view-sigs# this#)]
+          (reagent-data-views.client.component/update-subscriptions! this#))
-              (reagent-data-views.client.component/update-subscriptions! this# new-view-sigs#)))
 
         :component-function
         (fn ~args
-            ~@body)}))))
+          ~@body)})))

src/cljs/reagent_data_views/client/component.cljs

@@ -1,63 +1,62 @@
 (ns reagent-data-views.client.component
   (:require
+    [clojure.set :refer [difference]]
     [reagent.core :as r]
     [reagent.impl.util :refer [reagent-component?]]
     [reagent-data-views.client.core :as views]
-    [reagent-data-views.client.utils :refer [diff update-component-state!]]))
+    [reagent-data-views.client.utils :refer [update-component-state!]]))
-
-(defn subscribe!
-  "Subscribes a component to the given view-sigs.
-   NOTE: this function is only intended to be used internally by defvc."
-  [this view-sigs]
-  (assert (reagent-component? this))
-  (r/set-state this {:view-sigs view-sigs})
-  (views/subscribe! view-sigs))
 
 (defn unsubscribe-all!
   "Unsubscribes a component from all it's current view subscriptions.
    NOTE: this function is only intended to be used internally by defvc."
   [this]
   (assert (reagent-component? this))
-  (when-let [view-sigs (:view-sigs (r/state this))]
+  (let [last-used-view-sigs (:last-used-view-sigs (r/state this))]
-    (update-component-state! this #(dissoc % :view-sigs))
+    (views/unsubscribe! last-used-view-sigs)
-    (views/unsubscribe! view-sigs)))
+    (update-component-state! this #(dissoc % :used-view-sigs :last-used-view-sigs))))
+
+(defn prepare-for-render!
+  "Prepares the used-view/last-used-view sigs state for the upcoming
+   component render.
+   NOTE: this function is only intended to be used internally by defvc."
+  [this]
+  (assert (reagent-component? this))
+  (let [{:keys [used-view-sigs]} (r/state this)]
+    (r/set-state this {:used-view-sigs      #{}
+                       :last-used-view-sigs (or used-view-sigs #{})})))
 
 (defn update-subscriptions!
-  "Updates a component's view subscriptions to match the new full list
+  "Updates view subscriptions by checking what view-sigs were passed to
-   of view-sigs. Only changed view-sigs will cause a view subscription
+   any view-cursor calls during the most recent render and comparing
-   change to occur.
+   against the view-sigs that were used during the previous render.
+   Automatically subscribes to new view-sigs and unsubscribes from old
+   ones only as is needed.
    NOTE: this function is only intended to be used internally by defvc."
-  [this new-view-sigs]
+  [this]
   (assert (reagent-component? this))
-  (let [current-view-sigs (:view-sigs (r/state this))]
+  (let [{:keys [used-view-sigs last-used-view-sigs]} (r/state this)]
-    (when (not= current-view-sigs new-view-sigs)
+    (if (not= used-view-sigs last-used-view-sigs)
-      (let [sigs-to-sub (diff new-view-sigs current-view-sigs)
+      (let [sigs-to-unsub (vec (difference last-used-view-sigs used-view-sigs))
-            sigs-to-unsub (diff current-view-sigs new-view-sigs)]
+            sigs-to-sub   (vec (difference used-view-sigs last-used-view-sigs))]
-        (update-component-state! this #(assoc % :view-sigs new-view-sigs))
+        (views/update-subscriptions! sigs-to-sub sigs-to-unsub)
-        (views/update-subscriptions! sigs-to-sub sigs-to-unsub)))))
+        (r/set-state this {:used-view-sigs      #{}
-
+                           :last-used-view-sigs used-view-sigs})))))
-(defn- get-views-by-name [view-name view-sigs]
-  (filter #(= view-name (first %)) view-sigs))
 
 (defn view-cursor
-  "Returns a Reagent cursor that can be used to access the data for a view by
+  "Returns a Reagent cursor that can be used to access the data for a view.
-   looking up the corresponding view-sig by name in the current component's
+   If the view-sig is not currently subscribed to, the subscription will be
-   list of view subscriptions.
+   added automatically by the containing component, but this function will
+   return a cursor pointing to nil data until the server sends the initial
+   data for the new subscription (at which point a re-render is triggered).
 
-   This function can only be used within the component's render function.
+   This function can only be used with the render function of a component
+   defined using defvc.
 
-   If there are currently multiple subscriptions to views with the same name
+   NOTE: The data returned by this function is intended to be used in a
-   (using different arguments) an error is thrown.
+         read-only manner. Using this cursor to change the data will *not*
-
+         propagate the changes to the server."
-   NOTE: This function is intended to be used in a read-only manner. Using
+  [view-sig]
-         this cursor to change the data will *not* propagate to the server or
+  (let [this (r/current-component)]
-         any other clients currently subscribed to this view."
+    (assert (not (nil? this)) "view-cursor can only be used within a defvc component's render function.")
-  [view-name]
+    (update-component-state! this #(update-in % [:used-view-sigs] conj view-sig))
-  (assert (not (nil? (r/current-component))))
+    (views/->view-sig-cursor view-sig)))
-  (let [view-sigs   (->> (r/current-component) (r/state) :view-sigs)
-        match       (get-views-by-name view-name view-sigs)
-        num-matches (count match)]
-    (case num-matches
-      1 (views/view-sig-cursor (first match))
-      0 (throw (str "No matching view signature by the name \"" view-name "\"."))
-      (throw (str "More then one view signature by the name \"" view-name "\" found.")))))

src/cljs/reagent_data_views/client/core.cljs

@@ -1,8 +1,7 @@
 (ns reagent-data-views.client.core
   (:require
     [reagent.core :as r]
-    [clj-browserchannel-messaging.client :as browserchannel]
+    [clj-browserchannel-messaging.client :as browserchannel]))
-    [reagent-data-views.client.utils :refer [diff]]))
 
 ;; IMPORTANT NOTE:
 ;; We are using Reagent's built-in RCursor instead of the one provided by reagent-cursor
@@ -15,17 +14,18 @@
 
 (defonce view-data (r/atom {}))
 
-(defn view-sig-cursor
+(defn ->view-sig-cursor
-  "Returns a Reagent cursor that can be used to access the data for the view
+  "Creates and returns a Reagent cursor that can be used to access the data
-   corresponding with the view-sig.
+   for the view corresponding with the view-sig.
 
    Generally, for code in a component's render function, you should use
    reagent-data-views.client.component/view-cursor instead of using this
-   function directly.
+   function directly. Use of this function instead requires you to manage
+   view subscription/unsubscription yourself.
 
-   NOTE: This function is intended to be used in a read-only manner. Using
+   NOTE: The data returned by this function is intended to be used in a
-         this cursor to change the data will *not* propagate to the server or
+         read-only manner. Using this cursor to change the data will *not*
-         any other clients currently subscribed to this view."
+         propagate the changes to the server."
   [view-sig]
   (r/cursor [view-sig :data] view-data))
 
@@ -40,7 +40,7 @@
     (get-in @view-data path)))
 
 (defn- add-initial-view-data! [view-sig data]
-  (let [cursor (view-sig-cursor view-sig)]
+  (let [cursor (->view-sig-cursor view-sig)]
     (reset! cursor data)))
 
 (defn- remove-view-data! [view-sig]
@@ -57,7 +57,7 @@
   (concat existing-data insert-deltas))
 
 (defn- apply-deltas! [view-sig deltas]
-  (let [cursor (view-sig-cursor view-sig)]
+  (let [cursor (->view-sig-cursor view-sig)]
     (doseq [{:keys [refresh-set insert-deltas delete-deltas]} deltas]
       (if refresh-set         (reset! cursor refresh-set))
       (if (seq delete-deltas) (swap! cursor apply-delete-deltas delete-deltas))
@@ -85,7 +85,7 @@
 
 (defn subscribe!
   "Subscribes to the specified view(s). Updates to the data on the server will
-   be automatically pushed out. Use get-data-cursor to read this data and
+   be automatically pushed out. Use a 'view cursor' to read this data and
    render it in any component(s)."
   [view-sigs]
   (doseq [view-sig view-sigs]

src/cljs/reagent_data_views/client/utils.cljs

@@ -4,17 +4,6 @@
     [reagent.impl.component :as rcomp]
     [reagent.impl.util :refer [reagent-component?]]))
 
-(defn diff
-  "Given two vectors a and b, returns a vector that contains only the
-   items from a that do not also exist in b."
-  [a b]
-  (->> b
-       (reduce
-         (fn [item-a item-b]
-           (remove #(= % item-b) item-a))
-         a)
-       (vec)))
-
 ; TODO: relies on internal Reagent functionality. state-atom is not officially
 ;       part of the public Reagent API yet, but will probably be part of it in
 ;       the future. this function may need to be updated at that time.