From b6005bbe929ce09b0e088839d93b9a4f43fe07a7 Mon Sep 17 00:00:00 2001
From: Ahmed Anas <ahmed.anas@mixmax.com>
Date: Fri, 4 Jul 2025 15:15:01 +0400
Subject: [PATCH 1/2] fix: encodePaginationTokens to encode plain objects

---
 src/utils/query.ts | 51 +++++++++++++++++++++++++++-------------------
 1 file changed, 30 insertions(+), 21 deletions(-)

diff --git a/src/utils/query.ts b/src/utils/query.ts
index 7b8bf20..b75c4a4 100644
--- a/src/utils/query.ts
+++ b/src/utils/query.ts
@@ -23,6 +23,19 @@ export type PaginationResponse<T> = {
   hasNext: boolean;
 };
 
+/**
+ * Return true only for "simple" POJOs: `{}` created by object literals or
+ * `Object.create(null)`.  Arrays, class instances, Dates, BSON objects, etc.
+ * will return false.
+ */
+function isPlainObject(value: unknown): value is Record<string, any> {
+  if (value === null || typeof value !== 'object') return false;
+  const proto = Object.getPrototypeOf(value);
+  return proto === Object.prototype || proto === null;
+}
+
+
+
 /**
  * Helper function to encode pagination tokens.
  *
@@ -38,38 +51,34 @@ export type PaginationResponse<T> = {
  *
  * @returns void
  */
-function encodePaginationTokens(params: PaginationParams, response: PaginationResponse<any>): void {
+function encodePaginationTokens(
+  params: PaginationParams,
+  response: PaginationResponse<any>
+): void {
   const shouldSecondarySortOnId = params.paginatedField !== '_id';
 
-  if (response.previous) {
+  // ----- previous ----------------------------------------------------------
+  if (response.previous && isPlainObject(response.previous)) {
     let previousPaginatedField = objectPath.get(response.previous, params.paginatedField);
     if (params.sortCaseInsensitive) {
       previousPaginatedField = previousPaginatedField?.toLowerCase?.() ?? '';
     }
-    if (shouldSecondarySortOnId) {
-      if (
-        typeof response.previous === 'object' &&
-        response.previous !== null &&
-        '_id' in response.previous
-      ) {
-        response.previous = bsonUrlEncoding.encode([previousPaginatedField, response.previous._id]);
-      }
-    } else {
-      response.previous = bsonUrlEncoding.encode(previousPaginatedField);
-    }
+
+    response.previous = shouldSecondarySortOnId && '_id' in response.previous
+      ? bsonUrlEncoding.encode([previousPaginatedField, response.previous._id])
+      : bsonUrlEncoding.encode(previousPaginatedField);
   }
-  if (response.next) {
+
+  // ----- next --------------------------------------------------------------
+  if (response.next && isPlainObject(response.next)) {
     let nextPaginatedField = objectPath.get(response.next, params.paginatedField);
     if (params.sortCaseInsensitive) {
       nextPaginatedField = nextPaginatedField?.toLowerCase?.() ?? '';
     }
-    if (shouldSecondarySortOnId) {
-      if (typeof response.next === 'object' && response.next !== null && '_id' in response.next) {
-        response.next = bsonUrlEncoding.encode([nextPaginatedField, response.next._id]);
-      }
-    } else {
-      response.next = bsonUrlEncoding.encode(nextPaginatedField);
-    }
+
+    response.next = shouldSecondarySortOnId && '_id' in response.next
+      ? bsonUrlEncoding.encode([nextPaginatedField, response.next._id])
+      : bsonUrlEncoding.encode(nextPaginatedField);
   }
 }
 

From b2cbc8fea958a5bcd9ecffba5b4d10cf808bd4c5 Mon Sep 17 00:00:00 2001
From: Ahmed Anas <ahmed.anas@mixmax.com>
Date: Fri, 4 Jul 2025 16:14:12 +0400
Subject: [PATCH 2/2] feat: unit tests

---
 test/utils/query.test.ts | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/test/utils/query.test.ts b/test/utils/query.test.ts
index 321e8f8..16a4ed7 100644
--- a/test/utils/query.test.ts
+++ b/test/utils/query.test.ts
@@ -38,6 +38,26 @@ describe('encodePaginationTokens', () => {
     expect(response.previous).toEqual(bsonUrlEncoding.encode(['Test', '456']));
   });
 
+  it('encodes tokens when cursor is a plain object that lacks _id', () => {
+    const params = {
+      paginatedField: 'name',
+    };
+
+    const response = {
+      results: [],
+      previous: { name: 'Alpha' },   // ⬅️ no _id
+      hasPrevious: false,
+      next: { name: 'Beta' },        // ⬅️ no _id
+      hasNext: false,
+    } as any;
+
+    encodePaginationTokens(params, response);
+
+    expect(response.previous).toEqual(bsonUrlEncoding.encode('Alpha'));
+    expect(response.next).toEqual(bsonUrlEncoding.encode('Beta'));
+  });
+
+
   describe('generateCursorQuery', () => {
     it('generates an empty cursor query when no next or previous cursor is provided', () => {
       const params = {