Assertion Failed: You modified xy twice


I am new to ember.

I want to display async relations of a model but I am running into the You modified "model.posts" twice on <eui@model:user::ember271:vV63NgcG0b4R7pm0th0K> in a single render. error.

I am using the newly generated ember app with these modifications (I omitted the imports):


export default DS.Model.extend({
      message: DS.attr('string')


export default DS.Model.extend({
  name: DS.attr('string'),
  posts: DS.hasMany('post', { async: true })


export default Ember.Route.extend({
  model(params) {
    return'user', params._id);


export default Ember.Route.extend({
  model() {


{{#each model.posts as |post|}}

What am I doing wrong?

Thank you! Daniel


Do you happen to be using Ember Data version 2.14.2? If so there seems to be a bug that is causing this,

I’ve rolled back to 2.13.2 and everything is happy again.

Let me know if rolling back works… if not we have some digging todo :slight_smile:

Cheers, Benjamin


Hey Benjamin,

thank you very much! After rolling back to 2.13.2 it works es expected!

Since I am new to ember (but not to web development) I could not believe that this is impossible. I researched the web for like 2 days straight.

Again, many thanks!


It’s super rare that this happens, most of the time the thing to do is upgrade :grin:

Year, well… shit happens :slight_smile:

Funny thing is, in 15 years I never head to post in a forum for something like this. But I really couldn’t wrap my head around this one. And in 15 years I never run into a bug :smiley: I guess there really is a first for everything.