implemented bill update

app/lib/db-types.ts

@@ -1,16 +1,40 @@
 import { ObjectId } from "mongodb";
 
-export interface Location {
-    _id: string;
+/** Bill basic data */
+export interface LocationBase {
     name: string;
-    bills: Bill[];
     /** the value is encoded as yyyymm (i.e. 202301) */
     yearMonth: number;
 };
 
-export interface Bill {
+
+/** bill object in the form returned by MongoDB */
+export interface MongoLocation {
     _id: ObjectId;
+    bills: MongoBill[];
+};
+
+/** plain-object Location version */
+export interface PlainLocation {
+    id: string;
+    bills: PlainBill[];
+};
+
+
+/** Bill basic data */
+export interface BillBase {
     name: string;
     paid: boolean;
     document?: string|null;
 };
+
+/** bill object in the form returned by MongoDB */
+export interface MongoBill extends BillBase {
+    _id: ObjectId;
+};
+
+
+/** plain-object bill version */
+export interface PlainBill extends BillBase {
+    id: string;
+};