Add mechanism for data migrations

src/computersandblues/lodestone/app.cljs

@@ -4,6 +4,7 @@
             [clojure.string :as str]
             [clojure.pprint :as pprint]
             [computersandblues.lodestone.database :as db]
+            [computersandblues.lodestone.interop :refer [promise-all promise-resolve promise-reject]]
             [computersandblues.lodestone.match :refer [query->matching-xform]]
             [applied-science.js-interop :as j]))
 
@@ -34,15 +35,6 @@
 
 ;; Mastodon API helpers
 
-(defn- promise-all [xs]
-  (js/Promise.all (apply array xs)))
-
-(defn- promise-resolve [val]
-  (js/Promise.resolve val))
-
-(defn- promise-reject [val]
-  (js/Promise.reject val))
-
 (defn- now []
   (js/Date.now))
 
@@ -560,26 +552,45 @@
 
 ;; database
 
-(def db-version 3)
+;;; we provide two different kinds of migrations
+;;;
+;;; - structural migrations
+;;; - data migrations
+;;;
+;;; this is necessary due to the constraints imposed on us by indexeddb.
+;;;
+;;; structural migrations run in a callback after opening the database. they run
+;;; synchronously and do things like creates stores and indices. because they run
+;;; synchronously, they cannot modify any of the stored data.
+;;;
+;;; data migrations can do that! they run after all structural migrations for
+;;; the current database version have succeeded, and work on the open database.
+;;;
+;;; note that for each db-version, there needs to be at least one structural or
+;;; data migration. it is fine to have both for a single version, in which case
+;;; the structural migration will run first.
 
-(def migrations
-  {1 (fn migration-0001 [db _]
+(def db-version 4)
+
+(def structural-migrations
+  {1 (fn =0001-create-stores [db _]
        (db/create-object-store! db ::db/application {:keyPath "id"})
        (db/create-object-store! db ::db/posts {:keyPath "id"}))
-   2 (fn migration-0002 [_ txn]
+   2 (fn =0002-add-post-created-at-idx [_ txn]
        (-> (db/open-store txn ::db/posts "readwrite")
            (db/create-index! ::db/post-created-at "created_at" {:unique false})))
-   3 (fn migration-0003 [_ txn]
+   3 (fn =0003-add-post-internal-id-idx [_ txn]
        (-> (db/open-store txn ::db/posts "readwrite")
            (db/create-index! ::db/post-internal-id "internal_id" {:unique false})))})
 
-(defn- convert-internal-ids! []
-  ; TODO figure out when we can remove this again
-  (let [cursor (db/open-cursor ::db/posts ::db/all)
-        result (db/transduce-cursor (filter (comp string? (j/get :internal_id))) cursor)]
-    (.then result (fn [rows]
-                    (doseq [row rows]
-                      (db/put! ::db/posts (j/update! row :internal_id parse-long)))))))
+(def data-migrations
+  {4 (fn =0004-convert-internal-ids [db]
+       (let [cursor (db/open-cursor db ::db/posts ::db/post-internal-id ::db/all)
+             result (db/transduce-cursor (filter (comp string? (j/get :internal_id))) cursor)]
+         (.then result
+                (fn [rows]
+                  (promise-all (for [row rows]
+                                 (db/put! ::db/posts (j/update! row :internal_id parse-long))))))))})
 
 ;; go go go
 
@@ -589,8 +600,7 @@
 (defn init []
   (swap! state assoc :root (rd/create-root (js/document.querySelector "#root")))
   (render)
-  (-> (db/setup! ::database db-version migrations)
+  (-> (db/setup! ::database db-version structural-migrations data-migrations)
       (.then #(setup-application!))
-      (.then #(convert-internal-ids!))
       (.catch (fn [err]
                 (js/console.error ::db/setup! err)))))