Automattic/mongoose · error · MongooseError

`refPath` must be a string or a function that returns a stri

Error message

`refPath` must be a string or a function that returns a string, got ${util.inspect(refPath)}

What it means

Error "`refPath` must be a string or a function that returns a string, got ${util.inspect(refPath)}" thrown in Automattic/mongoose.

Source

Thrown at lib/helpers/populate/modelNamesFromRefPath.js:18

'use strict';

const MongooseError = require('../../error/mongooseError');
const isPathExcluded = require('../projection/isPathExcluded');
const lookupLocalFields = require('./lookupLocalFields');
const mpath = require('mpath');
const util = require('util');
const utils = require('../../utils');

const hasNumericPropRE = /(\.\d+$|\.\d+\.)/g;

module.exports = function modelNamesFromRefPath(refPath, doc, populatedPath, modelSchema, queryProjection) {
  if (refPath == null) {
    return [];
  }

  if (typeof refPath !== 'string') {
    throw new MongooseError('`refPath` must be a string or a function that returns a string, got ' + util.inspect(refPath));
  }

  if (queryProjection != null && isPathExcluded(queryProjection, refPath)) {
    throw new MongooseError('refPath `' + refPath + '` must not be excluded in projection, got ' +
      util.inspect(queryProjection));
  }

  // If populated path has numerics, the end `refPath` should too. For example,
  // if populating `a.0.b` instead of `a.b` and `b` has `refPath = a.c`, we
  // should return `a.0.c` for the refPath.

  if (hasNumericPropRE.test(populatedPath)) {
    const chunks = populatedPath.split(hasNumericPropRE);

    if (chunks[chunks.length - 1] === '') {
      throw new Error('Can\'t populate individual element in an array');
    }

View on GitHub (pinned to 49cdab0136)

When it happens

Trigger: Thrown at lib/helpers/populate/modelNamesFromRefPath.js:18 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of Automattic/mongoose@49cdab0136 (2026-08-21). Data as JSON: /api/errors/b0cc81a2bcf4c0dd. Report an issue: GitHub.