find() and find(id) triggering Ajax calls to the server - ember.js

Question

In my application, I have the common parent/child relationship in my route map.
App.Router.map(function () {
this.resource('strats', {path: "/"}, function() {
this.route('strat', {path: "/strat/:strat_id"});
});
});
My understanding is that when Ember first enters the parent route, it calls find() to get all models, which generally triggers an Ajax call to the server. Then when Ember subsequently transitions to a child route, it first calls find(), followed by find(id). If I'm using a data layer with an identity-map implementation (such as Ember-Data or Ember-Model), these subsequent calls to find() and find(id) should result in data being fetched from local memory, and Ember should not have to initiate another Ajax call to the server as a result of calls to these functions as long as the application is running. If this understanding is correct, then I should not have to implement find(id) on the server side.
I'm using Ember-Model in my application. As I'm navigating between routes, I see on the server side requests for an individual model coming through once in awhile, which means calls to find(id) are sometimes triggering Ajax calls to the server, which was unexpected. Where's the flaw in my logic described above?

Answer 1

Firstly, Ember itself only does what your model hooks tell it to do.
And those hooks are only called if you are visiting the route anew. I'll give some examples of this using your router above.
App.Router.map(function () {
this.resource('cow');
this.resource('strats', {path: "/"}, function() {
this.route('strat', {path: "/strat/:strat_id"});
});
});
I visit the strats route. The model hook for that route (StratsRoute) will be hit (in your case a find, returning multiple strats).
I visit the strat/1 route. The model hook for the route (StratsStratRoute) will be hit( find(1))
I visit the strat/2 route. The model hook for the route (StratsStratRoute) will be hit( find(2))
I visit the cow route (which is outside of the strats).
I visit the strat/1 route, the model hook for each route will be called, 1 at a time down to the strat route. The StratsRoute will be called, and until that model has been returned it will wait, once it's returned it will then go to the StratsStratRoute route and wait until that's resolved, once resolved it will continue rendering the page etc.
Interestingly Ember Model has an interesting feature, you can use find or fetch. find will build up a dummy record and return it immediately, and once the ajax is returned it'll update the model. fetch will return a promise, and once the ajax has returned and the record fully built it will resolve the promise.
Note, there is a bit of a race condition in the find approach. Imagine if you do find() in the strats route, then find(1) in the strat route. They will both resolve immediately (with dummy records) and both make calls to the server. The first call will be for all of the records (which might include 1) the second call is for record #1. So we just made 2 calls for record one, that was kind of a waste. In this instance fetch would have been better. Let's think about it with fetch. fetch in the strats route, now we wait til it's resolved. Once it's resolved (aka the server returned all the models) we hit the strat route, it does fetch(1) and instead of it hitting the server, it knows it already has model 1, it came down in the strats route, so it doesn't make an ajax request, and it resolves immediately.
Hopefully this clears up the dust a bit.