Meteor (Iron Router subscriptions): handling server errors with waitOn - mongodb

Question

I'm attempting to redirect my users to a 404 page (or even to home) if they stumble onto a page for which there is no database match.
My waitOn code (inside the Iron Router Route)
waitOn: function(){
return Meteor.subscribe('cars', this.params.slug);
},
My publish method:
Meteor.publish("cars", function (slug) {
var selectedCar = Cars.findOne({slug: slug})._id;
return [
Cars.find({ _id: selectedCar}),
Parts.find({carid: selectedCar}),
]
});
Everything is fine, except waitOn hangs whenever someone visits a page for which there is no matching Car (i.e the :slug doesn't match anything in the database)
Example Server error:
Exception from sub cars id CTusRZSAPqJaK9ws3 TypeError: Cannot read
property '_id' of undefined
I've tried all sorts of things as recommended on various blogs/posts, and still not sure how to deal with such server errors when waitOn is involved.
Has anyone been able to deal with such errors in their subscriptions?

Answer 1

In your current code you are not handling the case where findOne method might return undefined as a result.
Please modify your publication:
Meteor.publish("cars", function (slug) {
var selectedCar = Cars.findOne({slug: slug});
if (selectedCar) {
return [
Cars.find({ _id: selectedCar._id}),
Parts.find({carid: selectedCar._id}),
]
}
this.ready()
});
in above code if findOne returns an undefined result, we are calling the this.ready() method which will set the subscription ready.
on the client side if you don't receive any data in your subscription you can display the 404 message (item not found).
Also you should validate the slug, before querying. Just to avoid any nosql injection. for that you could use the check package.