Return ValidationError from post findOneAndUpdate middleware does not contain message

[jeremyml]

@vkarpov15 suggested the code below in this comment

schema.post('findOneAndUpdate', (result, next) =>{
  if (result.docField == 'invalidValue'){
    return next(new mongoose.Error.ValidationError('docField had an invalid value'));
  }
  // ...
});

But the ValidationError does not contain the custom message

docField had an invalid value

Instead the message is simply the canned message

Validation failed

This is the ValidationError in string from:

{
	"errors": {},
	"_message": "Validation failed",
	"message": "Validation failed",
	"name": "ValidationError"
}

I tested it in v 4.13.8 and v 5.0.7

[lineus]

hi @jeremyml. From what I can tell, it looks like @vkarpov15 was just helping with the async portion of the hook you suggested. After looking at the source for ValidationError, it would appear that if you give it a string instead of an instance of a model, your message will only ever be 'Validation failed'

function ValidationError(instance) {
  this.errors = {};
  this._message = '';
  if (instance && instance.constructor.name === 'model') {
    this._message = instance.constructor.modelName + ' validation failed';
    MongooseError.call(this, this._message);
  } else {
    this._message = 'Validation failed';
    MongooseError.call(this, this._message);
  }
  this.name = 'ValidationError';
  if (Error.captureStackTrace) {
    Error.captureStackTrace(this);
  } else {
    this.stack = new Error().stack;
  }
  if (instance) {
    instance.errors = this.errors;
  }
}

[lineus]

If you can live with an instance of Error the following works:

#!/usr/bin/env node
'use strict'

const mongoose = require('../lib/test_db')
const Schema = mongoose.Schema

const testSchema = Schema({
  docField: String
})

testSchema.post('findOneAndUpdate', (result, next) => {
  let err = new Error('invalid docfield value')
  err.name = 'ValidationError'
  
  if (result.docField === 'invalidValue') {
    return next(err)
  }
})

const Test = mongoose.model('test', testSchema)

const test = new Test({
  docField: 'valid'
})

let savedDoc = test.save()
savedDoc.then(() => {
  Test.findOneAndUpdate({
    _id: test.id
  }, { docField: 'invalidValue' }, { runValidators: true, new: true }, (err, res) => {
    if (err) { return console.error(err) }
    console.log(res)
  })
})

output:

InspiredMacPro:Help lineus$ ./mongoose5/6171/index.js 
{ ValidationError: invalid docfield value
    at Query.testSchema.post (/Users/lineus/dev/Help/mongoose5/6171/index.js:12:25)
    at callMiddlewareFunction (/Users/lineus/dev/Help/mongoose5/node_modules/kareem/index.js:399:23)
    at next (/Users/lineus/dev/Help/mongoose5/node_modules/kareem/index.js:193:9)
    at Kareem.execPost (/Users/lineus/dev/Help/mongoose5/node_modules/kareem/index.js:217:3)
    at _cb (/Users/lineus/dev/Help/mongoose5/node_modules/kareem/index.js:289:15)
    at _init (/Users/lineus/dev/Help/mongoose5/node_modules/mongoose/lib/query.js:2010:5)
    at model.Document.init (/Users/lineus/dev/Help/mongoose5/node_modules/mongoose/lib/document.js:370:5)
    at completeOne (/Users/lineus/dev/Help/mongoose5/node_modules/mongoose/lib/query.js:1996:12)
    at cb (/Users/lineus/dev/Help/mongoose5/node_modules/mongoose/lib/query.js:2368:14)
    at /Users/lineus/dev/Help/mongoose5/node_modules/mongoose/lib/query.js:2454:16
    at /Users/lineus/dev/Help/mongoose5/node_modules/mongoose/lib/utils.js:418:16
    at session.endSession (/Users/lineus/dev/Help/mongoose5/node_modules/mongodb/lib/utils.js:400:74)
    at ClientSession.endSession (/Users/lineus/dev/Help/mongoose5/node_modules/mongodb-core/lib/sessions.js:69:41)
    at args.push (/Users/lineus/dev/Help/mongoose5/node_modules/mongodb/lib/utils.js:397:17)
    at handleCallback (/Users/lineus/dev/Help/mongoose5/node_modules/mongodb/lib/utils.js:128:55)
    at /Users/lineus/dev/Help/mongoose5/node_modules/mongodb/lib/collection.js:2296:12 name: 'ValidationError' }
^C
InspiredMacPro:Help lineus$ 

[vkarpov15]

@jeremyml you're right, my example was incorrect

schema.post('findOneAndUpdate', (result, next) =>{
  if (result.docField == 'invalidValue'){
    var validationError = new mongoose.Error.ValidationError(null);
    validationError.addError('docField', new mongoose.Error.ValidatorError({ message: 'Invalid' })); 
    return next(validationError);
  }
  // ...
});

A ValidationError is a mapping of paths to ValidatorError instances, so you need to add one of those