.save() throws expection when using with co / koajs

[michelalbers]

Hi,

I use the latest master release in my koajs project and I encountered some strange issue:

try {
  userToSave = new User(body.user);
  (yield userToSave.save());
  return this.body = [userToSave._id];
} catch (_error) {
  e = _error;
  return this["throw"](500, e);
}

In my tests im trying to actively save a User which will not pass validation. Mongoose then throws an error: No listeners detected, throwing. Consider adding an error listener to your connection.

Even though I wrapped my JavaScript yield userToSave.save() statement in try-catch block the exception cannot be caught and therefore crashes my application 👎

Isn't that contradictionary to the promise pattern? Shouldn't it simply call Promise.reject and not throw an exception on it's own?

The part in mongoose causing this (lib/document.js:1433):

Document.prototype.$__handleReject = function handleReject(err) {
  // emit on the Model if listening
  if (this.listeners('error').length) {
    this.emit('error', err);
  } else if (this.constructor.listeners && this.constructor.listeners('error').length) {
    this.constructor.emit('error', err);
  } else if (this.listeners && this.listeners('error').length) {
    this.emit('error', err);
  } else if (this.db) {
    // emit on the connection
    if (!this.db.listeners('error').length) {
      err.stack = 'No listeners detected, throwing. Consider adding an error listener to your connection.\n' + err.stack
    }
    this.db.emit('error', err);
  } else {
    throw err;
  }
}

Update: Even when using the classic callback approach, the exceptions gets thrown. That can't be right or can it be?

Best,
Michel

[vkarpov15]

Thanks for pointing this out, I'll investigate.

[vizo]

I have same issue .... with normal callback from save ....

No listeners detected, throwing. Consider adding an error listener to your connection.
ValidationError: Path firstName is required.
at model.Document.invalidate (/node_modules/mongoose/lib/document.js:1040:32)
at /node_modules/mongoose/lib/document.js:985:16
at validate (/node_modules/mongoose/lib/schematype.js:632:7)
at /node_modules/mongoose/lib/schematype.js:653:9
at Array.forEach (native)
at SchemaString.SchemaType.doValidate (/node_modules/mongoose/lib/schematype.js:636:19)
at /node_modules/mongoose/lib/document.js:983:9
at process._tickCallback (node.js:419:13)

[justin-lau]

I am able to reproduce this issue in v3.9.7 mongoose test on the ES6 validate() method only:

$ MONGOOSE_DISABLE_STABILITY_WARNING=1 ./node_modules/.bin/mocha --harmony --grep "Documents in ES6 validate()" test/harmony

The test would fail with noErrorListener turned on:

db = start({ noErrorListener: 1 });

However, if I add a model level error listener to the test case that does nothing, the test passes:

M.on('error', function(){});

[joethaw]

I also encounter this issue where the exception still get past the try catch around save() function and crash the process. Like justin-lau mentioned above, the model level error listener does not catch that exception. The exception in my case was thrown in my custom validation function.

[vkarpov15]

Thanks @justin-lau, debugged it for me :) looks like its tricky to determine if there are listeners or not when using yield, so I'm just gonna get rid of that exception.