Promise chain friendly errors

[xpepermint]

Hi. I started using promises all over my code because it makes the code look beautiful. I really like this library but the problem is that errors are returned as Object not as instanceof some ValidationError class.

What I would propose is to wrap errors into validate.ValidationError class where you can still get an object calling toObject() method thus everything works the same way we just add a better support for promises.

Example:

  validate.async(req.body, contraints).then(function() {
    return Model.save(req.body);
  }).then(function(result) {
    res.status(201).json(result);
  }).catch(validate.ValidationError, function(err) {
    res.status(422).json(err);
  }).catch(function(err) {
    res.status(500).json(err);
  });

I would appreciate if we can do this small update. Thanks!

[ansman]

I had something like this before but it caused a bunch of problems (mostly because I extended the error with the result) but I suppose this feature makes sense and I do like clean code :)

I'll give it some thought for the next version.

[ansman]

This relates to #10 BTW.

Would the solution posted in that issue work for you?

validate.async(req.body, contraints).then(function() {
    return Model.save(req.body);
  }).then(function(result) {
    res.status(201).json(result);
  }).catch(Error, function(err) {
    res.status(500).json(err);
  }).catch(function(err) {
    res.status(422).json(err);
  });

[xpepermint]

Yeah, I saw that example. The problem is that usually the last catch is a system (unhandled) error which should not supposed to happen and must have a status 50X. I handle the last catch globally and a user gets only a simple error message, the rest is sent to a developer.

I really feel like the validator should return an instance of a class thus the error could be distinguished in try/catch block (promise). Maybe we could add it as configuration option or something.

The error class could look something like this:

module.exports = function ValidationError(params, message, options) {
  Error.captureStackTrace(this, this.constructor);
  this.name = this.constructor.name;
  this.params = params;
  this.message = message || 'Validation failed';
  this.options = options;
};

require('util').inherits(module.exports, Error);

[ansman]

Yeah, agreed.
I think I always assumed that the error callback would be on the promise returned from validate.async but in your case that isn't true.

I'll probably add a wrapAsyncErrors function that will create the result object.

[xpepermint]

Sounds good. Thanks!

[xpepermint]

Hey @ansman. Any progress on this?

[xpepermint]

I created a simple upgrade so I can move on. Please check PR #57.

[ansman]

Released in 0.8.0 (42e5cb3)