Automattic/mongoose · error · MongooseError

Cannot set special property `${last}` on a schema

Error message

Cannot set special property `${last}` on a schema

What it means

Error "Cannot set special property `${last}` on a schema" thrown in Automattic/mongoose.

Source

Thrown at lib/schema.js:1306

      return mapPath;
    }

    // Look if a parent of this path is mixed
    schematype = this.hasMixedParent(cleanPath);
    if (schematype != null) {
      return schematype;
    }

    // subpaths?
    return hasNumericSubpathRegex.test(path)
      ? getPositionalPath(this, path, cleanPath)
      : undefined;
  }

  const subpaths = path.indexOf('.') === -1 ? [path] : path.split('.');
  const last = subpaths.pop();
  if (utils.specialProperties.has(last)) {
    throw new MongooseError('Cannot set special property `' + last + '` on a schema');
  }

  // some path names conflict with document methods
  const firstPieceOfPath = subpaths.length === 0 ? last : subpaths[0];
  if (Object.hasOwn(reserved, firstPieceOfPath) && !this.options.suppressReservedKeysWarning) {
    const errorMessage = `\`${firstPieceOfPath}\` is a reserved schema pathname and may break some functionality. ` +
      'You are allowed to use it, but use at your own risk. ' +
      'To disable this warning pass `suppressReservedKeysWarning` as a schema option.';

    utils.warn(errorMessage);
  }

  if (typeof obj === 'object' && utils.hasUserDefinedProperty(obj, 'ref')) {
    validateRef(obj.ref, path);
  }

  // update the tree
  let branch = this.tree;

View on GitHub (pinned to 49cdab0136)

When it happens

Trigger: Thrown at lib/schema.js:1306 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/9fa309019ef1bb57. Report an issue: GitHub.