DataSync: Prepend new records if the query is sorted newest first

Author: mpscholten

lib/IHP/DataSync/ihp-datasync.js

@@ -144,6 +144,9 @@ class DataSyncController {
     }
 }
 
+const APPEND_NEW_RECORD = 0;
+const PREPEND_NEW_RECORD = 1;
+
 class DataSubscription {
     constructor(query) {
         if (typeof query !== "object" || !('table' in query)) {
@@ -164,6 +167,21 @@ class DataSubscription {
 
         this.getRecords = this.getRecords.bind(this);
         this.subscribe = this.subscribe.bind(this);
+
+        // When a new record is inserted, do we put it at the end or at the beginning?
+        this.newRecordBehaviour = this.detectNewRecordBehaviour();
+    }
+
+    detectNewRecordBehaviour() {
+        // If the query is ordered by the createdAt column, and the latest is at the top
+        // we want to prepend new record
+        const isOrderByCreatedAtDesc = this.query.orderByClause.length > 0 && this.query.orderByClause[0].orderByColumn === 'createdAt' && this.query.orderByClause[0].orderByColumn === 'createdAt';
+
+        if (isOrderByCreatedAtDesc) {
+            return PREPEND_NEW_RECORD;
+        }
+
+        return APPEND_NEW_RECORD;
     }
 
     async createOnServer() {
@@ -251,7 +269,8 @@ class DataSubscription {
     }
 
     onCreate(newRecord) {
-        this.records = [...this.records, newRecord];
+        const shouldAppend = this.newRecordBehaviour === APPEND_NEW_RECORD;
+        this.records = shouldAppend ? [...this.records, newRecord] : [newRecord, ...this.records];
         this.updateSubscribers();
     }