Workaround of issues with chaining/nesting under @each in computed properties/ bound observers: https://github.com/emberjs/ember.js/issues/541

gistfile1.txt

I wanted to do something like this:

App.ApplicationController = Ember.Controller.extend
  selectedAccounts: (->
    accounts = []
    (@get 'currentUser.entities').forEach (entity)->
      accounts.pushObjects entity.get('accounts').filterProperty 'selected'
    accounts
  ).property('currentUser.entities.@each.accounts.@each.selected')



To workaround, I did this:

App.ApplicationController = Ember.Controller.extend
  selectedAccounts: (->
    accounts = []
    (@get 'currentUser.entities').forEach (entity)->
      accounts.pushObjects entity.get('selectedAccounts')
    accounts
  ).property('currentUser.entities.@each.selectedAccounts')

App.Entity = DS.Model.extend
  selectedAccounts: (->
    (@get 'accounts').filterProperty 'selected'
  ).property 'accounts.@each.selected'

Yes, this is pretty much what we ended up doing as well; but note that this will likely still give you horrible quadratic performance, because of the way changes propagate. In other words, as soon as you throw more than a handful of accounts at it, it will grind to a halt.

The usual solution is to serve down the selectedAccounts list from the server, instead of trying to compute it.

(Single @each is bad already, but I seem to recall that simulating nested @each gets you tangled up even worse.)

Hah, just ran into some fresh work that's been done on array CP performance:

https://github.com/emberjs/ember.js/tree/master/packages/ember-runtime/lib/computed
emberjs/ember.js@fc6e2f5

See also http://emberjs.com/blog/2013/08/29/ember-1-0-rc8.html , section Array Computed on how to get these things working without ruining performance (hopefully).