feat: implement multiGet function

Author: kidroca

lib/Onyx.js

@@ -36,34 +36,65 @@ deferredInit.promise = new Promise((res, rej) => {
 });
 
 /**
- * Get some data from the store
+ * Get multiple keys in a single batch
  *
- * @param {string} key
- * @returns {Promise<*>}
+ * @param {string[]} keys
+ * @returns {Promise<Record<string, *>>} - an object of key -> value mapping
  */
-function get(key) {
-    // When we already have the value in cache - resolve right away
-    if (cache.hasCacheForKey(key)) {
-        return Promise.resolve(cache.getValue(key));
-    }
+function multiGet(keys) {
+    const [fromCache, hardReads] = _.partition(
+        keys,
+        key => cache.hasCacheForKey(key) || cache.hasPendingTask(`get:${key}`)
+    );
+
+    // Init a list of tasks containing any pending reads from storage
+    const tasks = fromCache
+        .filter(key => cache.hasPendingTask(`get:${key}`))
+        .map(key => Promise.resolve(cache.getTaskPromise(`get:${key}`)));
+
+    // Append a task for any remaining "hard reads" the current list
+    if (hardReads.length > 0) {
+        const readKeysFromStorage = AsyncStorage.multiGet(hardReads)
+            .then(pairs => pairs.forEach(([key, val]) => {
+                const parsed = val && JSON.parse(val);
+                cache.set(key, parsed || null);
+            }));
 
-    const taskName = `get:${key}`;
+        tasks.push(readKeysFromStorage);
 
-    // When a value retrieving task for this key is still running hook to it
-    if (cache.hasPendingTask(taskName)) {
-        return cache.getTaskPromise(taskName);
+        /* Capture a resolver for potential multiGet calls that happen while we retrieve keys
+        * example one one call retrieves keys A,B,C another call retrieves B,C,D
+        * we don't need to start a new read for B,C we'll hook them from the first call
+        */
+        hardReads.forEach((key) => {
+            cache.captureTask(`get:${key}`, readKeysFromStorage.then(() => cache.getValue(key)));
+        });
     }
 
-    // Otherwise retrieve the value from storage and capture a promise to aid concurrent usages
-    const promise = AsyncStorage.getItem(key)
-        .then((val) => {
-            const parsed = val && JSON.parse(val);
-            cache.set(key, parsed);
-            return parsed;
-        })
-        .catch(err => logInfo(`Unable to get item from persistent storage. Key: ${key} Error: ${err}`));
+    // Return a grouped result
+    return Promise.all(tasks)
+        .then(() => {
+            /* At this point we have everything in cache
+            * Instead of searching for the value inside the result, we can retrieved it by key from cache */
+            const result = _.chain(keys)
+                .map(key => [key, cache.getValue(key)])
+                .object()
+                .value();
 
-    return cache.captureTask(taskName, promise);
+            return result;
+        });
+}
+
+/**
+ * Get some data from the store
+ *
+ * @param {string} key
+ * @returns {Promise<*>}
+ */
+function get(key) {
+    /* We use multiGet as it will batch multiple calls and flush them on the next iteration of
+    * the event loop. AsyncStorage uses `setImmediate` to do this internally */
+    return multiGet([key]).then(result => result[key]);
 }
 
 /**
@@ -781,6 +812,7 @@ function applyDecorators() {
     // Re-assign with decorated functions
     /* eslint-disable no-func-assign */
     get = decorate.decorateWithMetrics(get, 'Onyx:get');
+    multiGet = decorate.decorateWithMetrics(multiGet, 'Onyx:multiGet');
     set = decorate.decorateWithMetrics(set, 'Onyx:set');
     multiSet = decorate.decorateWithMetrics(multiSet, 'Onyx:multiSet');
     clear = decorate.decorateWithMetrics(clear, 'Onyx:clear');