Meteor Iron-Router: why isn't this routing setup (with waitOn and data functions) working correctly?

Question

Using Iron-Router 1.0.3 and Meteor 1.0.

I have this route defined:

Router.route('audit', {
    path: '/audit/:audit_id/',
    template: 'audit',
    data: function() {
        audit = Audits.findOne({_id: this.params.audit_id});
        lineitems = LineItems.find(JSON.parse(audit.query));
        return {
            audit: audit,
            lineitems: lineitems
        }
    },
    waitOn: function () {
        return [
            Meteor.subscribe('audits'),
            Meteor.subscribe('lineitems', this.params.audit_id),
        ]
    }
});

Objects in the Audits collection have the following structure:

{
    _id: 'timestamped-id-that-I-generate',
    name: 'some name',
    query: JSON.stringify({'$and': [list of query conditions here]})
}

When I go to this route I get the following error in my console:

Uncaught TypeError: Cannot read property 'query' of undefined

But if I go to my browser console, I can examine the Audits collections and I see that the Audit object with the appropriate _id and query exists as expected.

Incidentally, the publish method for the lineitems on the server side will simply look up the same audit object and publish the line items that match it's query.

(I have to serialize the query back and forth via JSON because otherwise the query object would contain field names that violate MongoDB regulations.)

Answer 1

As of this writing, Iron Router's data hook may run multiple times when a route is evaluated. You can assume it will run once before the subscriptions are ready, and again afterward. Because it will run prior to your subscriptions being ready, you need to assume that Audits.findOne will return undefined at least once. You have two choices:

1. Check for this.ready() in your data hook:

data: function() {
  if (this.ready()) {
    audit = Audits.findOne({_id: this.params.audit_id});
    lineitems = LineItems.find(JSON.parse(audit.query));
    return {audit: audit, lineitems: lineitems};
  }
}

2. Use a guard:

data: function() {
  audit = Audits.findOne({_id: this.params.audit_id});
  if (audit && audit.query) {
    lineitems = LineItems.find(JSON.parse(audit.query));
    return {audit: audit, lineitems: lineitems};
  }
}

A combination of the two may actually be appropriate if: (a) you don't have any audits, or (b) not all audits have a query.