mongoose difference between pre save and validate? When to use which one? - node.js

Question

Currently I am using pre('save') to do validation:
UserSchema.pre('save', true, function(next, done) {
var self = this //in case inside a callback
var msg = helper.validation.user.username(self.username)
if (msg) {
self.invalidate('username', msg)
done(helper.getValidationError(msg))
}
else
done()
next()
})
The helper module has a function that accepts an input and returns error message.
exports.user = {
username: function(input) {
if (!input)
return 'username is required'
var min = 3
var max = 10
if (input.length < min)
return 'username min of length is ' + min
if (input.length > max)
return 'username max of length is ' + max
return null
}
}
There is another api validate to do similar things. What's the difference between them and which one should I use in what cases?

Answer 1

Update:
The validation is performed before the user defined hooks. You can follow this github post, where the contributor states,
not implementing this. validating first gives us a chance to stop
before continuing into user defined hooks which may include async
updates to other collections.
if we need validation to run again after we make a change from inside
a hook we can always manually run this.validate(next).
Outdated:
Yeah, there is a small difference i know.
Pre hooks are executed before validations.
There is a closed issue on github asking for validation before pre hooks, https://github.com/Automattic/mongoose/issues/400.
And also there is a reason for not having validation before pre hooks, stated in the same link by #kamholz:
Say you have two fields, foo and fooSort, both are required. fooSort is a
lowercased or otherwise transformed version of foo to be used in
sorting. Since fooSort can be automatically generated, it makes sense
to do so in a pre-save hook. But since validation runs first, it will
fail before the pre-save hook runs and has a chance to fill in the
fooSort value. It isn't a question of being able to run validation
again manually.
Again, if you want to validate something and then need the hook for post validate:
UserSchema.post('validate', function(next){
console.log("post validate called");
next();
});
So for summary, the one difference i see is,
you can use both as long as you get inputs to save in db directly without altering anything (only validation).
If you are altering anything you have to use pre save hook.

Answer 2

The above answer is incorrect. If you go to: https://github.com/Automattic/mongoose/issues/400 and read the responses to the topic from the mongoose contributor you'll see that he notes they are run before on purpose.
The topic is named: Validation should run after all other pre-save hooks
Mongoose contributor aheckmann states that:
right now its running before them
not implementing this. validating first gives us a chance to stop before continuing into user defined hooks which may include async updates to other collections.