Router-level middleware order using Express.js - rest

Question

I have the following routers:
/* GET /users/username */
router.get("/:username", function(req, res, next) {
User.findOne({
username: req.params.username
}).exec(function(err, user) {
if (err) return next(error);
res.json(user);
});
});
/* GET /users/id */
router.get("/:id", function(req, res, next) {
User.findById(req.params.id, function(err, user) {
if (err) return next(err);
res.json(user);
});
});
In the above order, /* GET /users/id */ will return null, and if I swap the order the /* GET /users/username */ will result in this error:
Cast to ObjectId failed for value "Guest" at path "_id" for model "User"
Basically, the second middleware is being ignored. However, both are needed for different behaviors. I'm using AngularJS $resource to interact with RESTful server-side data sources.
Why can't I use both simultaneously? Why is the second middleware ignored?
In which order should these two routers be to both working?

Answer 1

The second middleware is ignored, because the url pattern is the same... How do you want the router make the differenciation between an 'username' or an 'id';
You've got to check if it's an id first per exemple.
router.get("/:username", function(req, res, next) {
const username = req.params.username;
if (!isNaN(parseInt(username)) { // <------ Check if it's an ID
next();
} else {
User.findOne({
username: req.params.username
}).exec(function(err, user) {
if (err) return next(error);
res.json(user);
});
}
});
/* GET /users/id */
router.get("/:id", function(req, res, next) {
User.findById(req.params.id, function(err, user) {
if (err) return next(err);
res.json(user);
});
});

Answer 2

It's better to route by doing:
router.route('your/route').get(aJsFile.function);
Then, instead of the exec, just write
attributes: ['id', 'username']
where: {username: username}
Or something like this.