refactor(nocodb): add / revise comments

packages/nocodb/src/models/Model.ts

@@ -488,7 +488,7 @@ export default class Model implements TableType {
                 .format('YYYY-MM-DD HH:mm:ssZ');
             }
           } else {
-            // TODO(timezone): keep ext db as it is
+            // External DB - keep it as it is
             val = dayjs(val).format(
               isMySQL ? 'YYYY-MM-DD HH:mm:ss' : 'YYYY-MM-DD HH:mm:ssZ',
             );

packages/nocodb/src/version-upgrader/ncDateTimeUpgrader.ts

@@ -28,6 +28,11 @@ function getTnPath(knex: XKnex, tb: Model) {
   }
 }
 
+// This upgrader is to update all datetime fields in xcdb base due to the datetime changes
+// ref: https://github.com/nocodb/nocodb/pull/5505
+// Originally, for XCDB-based projects, we store the local time in DB and display local time in UI
+// After the above PR, we store UTC time in DB and display local time in UI
+// Therefore, we convert all the target datetime to UTC format in DB
 export default async function ({ ncMeta }: NcUpgraderCtx) {
   const bases: BaseType[] = await ncMeta.metaList2(null, null, MetaTable.BASES);
   for (const _base of bases) {