creating an ember-data application serialzer

I've been trying to use ember data for a few days now. The problem is the api I have does not match the strcuture ember-data would like to receive.

item:

{
    "data": {
        "id": 1,
        "username": "rodzzlessa",
        "slug": "rodzzlessa"
     }
}

collection:

{
"data": [
    {
        "id": 34,
        "name": "HDG common nails 50lbs",
        "slug": "hdg-common-nails-50lbs4569",
        "description": "Accusantium ipsam impedit omnis sint dolorum.",
        "image_src": "nail-box-angle.png",
        "categories": {
            "data": [
                {
                     "id": 2,
                     "name": "nails",
                    "image_src": "nails-icon.png"
                }
             ]
         }
     }
  ]
}

from what I've seen I need to modify the extractSingle and extractArray methods. There really isn't an online resource showing what the methods are really doing and how to modify them. I check the ember-data api guide but the example is so specific and its not an application serializer so it seems much easier the problem they are solving. I tried finding an ember-data book but they don't exist yet. Are there any online resources to help me?