core: handle case when updating item while a push is ongoing

packages/core/src/api/sync/collector.ts

@@ -46,6 +46,7 @@ class Collector {
     for (const itemType of SYNC_ITEM_TYPES) {
       const collectionKey = SYNC_COLLECTIONS_MAP[itemType];
       const collection = this.db[collectionKey].collection;
+      let pushTimestamp = Date.now();
       for await (const chunk of collection.unsynced(chunkSize, isForceSync)) {
         const items = await this.prepareChunk(chunk, key);
         if (!items) continue;
@@ -54,8 +55,20 @@ class Collector {
         await collection.update(
           chunk.map((i) => i.id),
           { synced: true },
-          { sendEvent: false }
+          {
+            sendEvent: false,
+            // EDGE CASE:
+            // Sometimes an item can get updated while it's being pushed.
+            // The result is that its `synced` property becomes true even
+            // though it's modification wasn't yet synced.
+            // In order to prevent that, we only set the `synced` property
+            // to true for items that haven't been modified since we last ran
+            // the push. Everything else will be collected again in the next
+            // push.
+            condition: (eb) => eb("dateModified", "<=", pushTimestamp)
+          }
         );
+        pushTimestamp = Date.now();
       }
     }
   }

packages/core/src/database/sql-collection.ts

@@ -226,7 +226,14 @@ export class SQLCollection<
   async update(
     ids: string[],
     partial: Partial<SQLiteItem<T>>,
-    options: { sendEvent: boolean } = { sendEvent: true }
+    options: {
+      sendEvent: boolean;
+      condition?: ExpressionOrFactory<
+        DatabaseSchema,
+        keyof DatabaseSchema,
+        SqlBool
+      >;
+    } = { sendEvent: true }
   ) {
     if (!this.sanitizer.sanitize(this.type, partial)) return;
 
@@ -237,6 +244,7 @@ export class SQLCollection<
           await tx
             .updateTable<keyof DatabaseSchema>(this.type)
             .where("id", "in", chunk)
+            .$if(!!options.condition, (eb) => eb.where(options.condition!))
             .set({
               ...partial,
               dateModified: Date.now(),