BigInt/Int64 negative value parse error

[GaussETH]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Mongoose version

8.9.5

Node.js version

22

MongoDB server version

8.0.4

Typescript version (if applicable)

No response

Description

BigInt field with negative value parse error in latest mongoose(8.9.5), bug works well in 7.8.4.

Steps to Reproduce

Model

const UserRewardSchema = new Schema({
  chainId: {
    type: Number,
    required: true,
    immutable: true,
  },
  account: {
    type: String,
    required: true,
    index: true,
    immutable: true,
  },
  value: {
    type: BigInt,
    required: true,
    default: 0n,
  },
}, {
  versionKey: false,
  timestamps: true,
  collection: 'userRewards',
})
UserRewardSchema.index({ chainId: 1, account: 1 }, { unique: true })

export const UserReward = model('UserReward', UserRewardSchema)

import { connect } from "mongoose"
import { DB_URI } from "#common/env.js"

/**
 * @type {import('mongoose').Mongoose}
 */
let mongoose

export const connectDb = async () => {
  if (!mongoose) {
    mongoose = await connect(DB_URI, { useBigInt64: true })
    mongoose.set("transactionAsyncLocalStorage", true).set('strictQuery', true)
  }

  return mongoose
}

const items = await UserReward.find({ account: 'xxxxx' })
    .select('-_id')
    .lean()

console.log(items)

Expected Behavior

[sudhackar]

Simpler repro

diff --git a/test/bigint.test.js b/test/bigint.test.js
index e3d00418e..14e3bddac 100644
--- a/test/bigint.test.js
+++ b/test/bigint.test.js
@@ -88,7 +88,7 @@ describe('BigInt', function() {
     let Test;

     before(async function() {
-      db = await start();
+      db = await start({useBigInt64: true});

       const schema = new Schema({
         myBigInt: BigInt
@@ -114,14 +114,14 @@ describe('BigInt', function() {
     });

     it('becomes a bigint with lean using useBigInt64', async function() {
-      await Test.create({ myBigInt: 7n });
+      await Test.create({ myBigInt: 18446744073709551613n });

       const doc = await Test.
-        findOne({ myBigInt: 7n }).
+        findOne({ myBigInt: 18446744073709551613n }).
         setOptions({ useBigInt64: true }).
         lean();
       assert.ok(doc);
-      assert.strictEqual(doc.myBigInt, 7n);
+      assert.strictEqual(doc.myBigInt, -3n);
     });

     it('can query with comparison operators', async function() {

This test fails on current version - but I think its not due to code changes in mongoose

[sudhackar]

git bisect points to 750c6e2

this will pass the test mentioned above

diff --git a/package.json b/package.json
index 663a81830..990478ec3 100644
--- a/package.json
+++ b/package.json
@@ -19,9 +19,9 @@
   ],
   "license": "MIT",
   "dependencies": {
-    "bson": "^6.10.1",
+    "bson": "5.5.0",
     "kareem": "2.6.3",
-    "mongodb": "~6.12.0",
+    "mongodb": "5.7.0",
     "mpath": "0.9.0",
     "mquery": "5.0.0",
     "ms": "2.1.3",

[vkarpov15]

This issue seems to be indicative of not setting useBigInt64. For example, the following script stores the correct value normally, but stores -3n if useBigInt64 option is commented out. Did you always have await connect(DB_URI, { useBigInt64: true }) or did you recently add useBigInt64?

'use strict';

const mongoose = require('mongoose');
mongoose.set('debug', true);

(async function() {
  await mongoose.connect('mongodb://127.0.0.1:27017/mongoose_test', { useBigInt64: true });

  const schema = new mongoose.Schema({
    myBigInt: BigInt
  });
  const Test = mongoose.model('Test', schema);
  await Test.deleteMany({});

  const { _id } = await Test.create({ myBigInt: 18446744073709551613n });
  const doc = await Test.findById(_id);
  doc.markModified('myBigInt');
  await doc.save();

  console.log(await Test.findById(_id));
})();

This does bring up a good point that useBigInt64 with save() is a bit of a footgun. Without useBigInt64, BigInts can lose precision when updating documents in place. We will work on fix.