TypeError: Cannot read properties of undefined (reading '$__') when creating document with array of objects

[LimChorngUan]

Prerequisites

• I have written a descriptive issue title

Mongoose version

8.15.1

Node.js version

22.14.0

MongoDB version

6.16.0

Operating system

macOS

Operating system version (i.e. 20.04, 11.3, 10)

15.4.1

Issue

Calling .create() on a schema with a simple array of objects throws
TypeError: Cannot read properties of undefined (reading '$__')
in the latest mongoose.

Minimal Repro Code in test file
Jest version: ^29.7.0

import mongoose from "mongoose";

const TestSchema = new mongoose.Schema({
  name: String,
  array: [
    {
      value: Number,
    },
  ],
});

const TestModel = mongoose.model("TestModel", TestSchema);

test("test mongoose schema creation", async () => {
  await TestModel.create([
    {
      name: "Doc1",
      array: [
        {
          value: 123,
        },
      ],
    },
  ]);

  console.log("Create succeeded!");

  expect(true).toBe(true);
});

Error:

TypeError: Cannot read properties of undefined (reading '$__')
    at _getPathsToValidate ...

Notes:

• Works on mongoose version 8.13.0, fails on 8.14.0

[vkarpov15]

I'm unable to repro, the following script:

const mongoose = require('mongoose');
mongoose.connect('mongodb://127.0.0.1:27017/mongoose_test');

const TestSchema = new mongoose.Schema({
  name: String,
  array: [
    {
      value: Number,
    },
  ],
});

const TestModel = mongoose.model("TestModel", TestSchema);

test("test mongoose schema creation", async () => {
  await TestModel.create([
    {
      name: "Doc1",
      array: [
        {
          value: 123,
        },
      ],
    },
  ]);

  console.log("Create succeeded!");

  expect(true).toBe(true);
});

Works fine:

$ ./node_modules/.bin/jest 
  console.log
    Create succeeded!

      at Object.log (index.spec.js:27:11)

 PASS  ./index.spec.js
  ✓ test mongoose schema creation (31 ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        0.331 s, estimated 1 s
Ran all test suites.
Jest did not exit one second after the test run has completed.

'This usually means that there are asynchronous operations that weren't stopped in your tests. Consider running Jest with `--detectOpenHandles` to troubleshoot this issue.
^C
$ npm list
jesttest@ /home/v/Desktop/MongoDB/troubleshoot-mongoose/jesttest
├── jest@29.7.0
└── mongoose@8.14.3

$ 

Are you using any plugins or any other packages? Also, what does your jest config look like?

[LimChorngUan]

Hey @vkarpov15 thanks so much for the quick reply and help verifying. It's good to know that you aren't able to reproduce, I'm trying to narrow down if it's our jest config or other packages issues.

Other related packages could be:

• mongodb-memory-server: ^10.1.4,
• @payloadcms/db-mongodb: 3.43.0 (We are using Payload CMS)

Here's how our jest config look like:

import type { Config } from "jest";

import nextJest from "next/jest";
import env from "./src/constants/env";

const createNextJest = nextJest({ dir: "./" });

const config: Config = {
  clearMocks: true,
  collectCoverage: Boolean(env.CI) === true,
  coverageDirectory: "coverage",
  coverageProvider: "v8",
  reporters: [
    "default",
    [
      "jest-junit",
      {
        outputDirectory: "report",
        outputName: "report.xml",
      },
    ],
  ],
  resetMocks: true,
  resetModules: true,
  testEnvironment: "node",
  testLocationInResults: true,
  testPathIgnorePatterns: ["/node_modules/", "/dist/", "/e2e/"],
  transform: {
    "^.+\\.(t|j)sx?$": [
      "ts-jest",
      {
        isolatedModules: true,
        useESM: true,
        tsconfig: {
          // Override any tsconfig settings specifically for tests
          module: "ESNext",
          moduleResolution: "node",
        },
      },
    ],
  },
  extensionsToTreatAsEsm: [".ts", ".tsx"],
  moduleNameMapper: {
    "^@/(.*)$": "<rootDir>/src/$1",
    "^@payload-config$": "<rootDir>/src/payload.config.ts",
    "^payload/generated-types$": "<rootDir>/src/generated-types.ts",
  },
  transformIgnorePatterns: ["/node_modules/(?!(\\.pnpm|@payloadcms))"],
};

export default createNextJest(config);

[vkarpov15]

It looks like you're using TypeScript and pnpm as well, can you please confirm your TypeScript config+version and pnpm version?

[LimChorngUan]

typescript: 5.8.3
pnpm: 10.2.1

ts config:

{
  "compilerOptions": {
    "baseUrl": ".",
    "lib": ["dom", "dom.iterable", "esnext"],
    "allowJs": true,
    "skipLibCheck": true,
    "strict": true,
    "noEmit": true,
    "esModuleInterop": true,
    "module": "esnext",
    "moduleResolution": "bundler",
    "resolveJsonModule": true,
    "isolatedModules": true,
    "jsx": "preserve",
    "incremental": true,
    "plugins": [
      {
        "name": "next"
      }
    ],
    "paths": {
      "@/*": ["./src/*"],
      "@payload-config": ["./src/payload.config.ts"],
      "payload/generated-types": ["src/generated-types.ts"]
    },
    "target": "ES2022",
  },
  "include": [
    "next-env.d.ts",
    "**/*.ts",
    "**/*.tsx",
    "jest.config.ts",
    ".next/types/**/*.ts",
  ],
  "exclude": ["node_modules", ".pnpm-store"]
}

[vkarpov15]

I've been able to repro the issue with the specified TSConfig and Jest config, with Next-specific stuff removed and using npm rather than pnpm. I'm investigating the root cause.

[vkarpov15]

I did some digging, it looks like this issue was fixed by #15471 - it will go away if you upgrade to Mongoose ^8.15.1.

I was also able to fix this issue by unsetting resetModules in your Jest config. That option looks like it clears Node's require() cache and makes it so that Mongoose's internals end up with a different copy of the Mongoose module than the one you're using in your test file. Is there a reason why you're using resetModules?