I was wondering if I could get an extra pair of eyes on this JSBin: http://jsbin.com/naperubu/1/edit?js,output
As far as I can tell I’ve done the right thing as per the docs, but I get the error TypeError: Cannot read property 'typeKey' of undefined
Apologies if I’ve missed something obvious it’s 5.30 on a Friday 
I modified your jsbin : jsbin please take a look is that what you want? Embedded records with ember data lil bit tricky with real REST server, I spent few days trying to make them work but with no success and decided to side loaded them in REST adapter serializer
Thank you @alekso I see what you did there!
Unfortunately the payload from our API will be like that of my original JSBin example - is it even possible to do out of the box? Or would I have to write a custom deserializer?
I dont believe it will work out of the box. For me it wasnt. Did you saw this article of Transition.md ?
My server API returns relationships as embedded too and I just did overwrite extract single and extractArray as described in link I mentioned above. And its kinda working 
. If you want to support native embedded you should implement EmbeddedRecordsMixin, but I found this not easy job because you need to download it as separate package and it works with activemodel-adapter package. As I know activemodel is Rails specific adapter, but may be I’m wrong. I suggest you to make some research because I’m also writing my first app and not emberjs expert so dont want to put you on wrong way :). It will be great if you will share your solution as well here
BR
Alex
Ah ha,
I managed to create what I was after by using ActiveModelSerializer instead of RESTSerializer. I’m not sure why it doesn’t work with RESTSerializer
Got it… changing the URLS in the above JSBin from beta to canary works.