EmberJS Data HasMany relationship parent jon contains whole object not ids

EmberJS Data HasMany relationship parent jon contains whole object not ids

App.Message = someParentClass.extend({
    childMessages: DS.hasMany('ChildMessage'),
    message:DS.attr('string',{defaultValue: ""})
}

App.ChildMessage = someParentClass.extend({
    message: DS.attr('string',{defaultValue: ""}),
    code:DS.attr('string',{defaultValue: ""})
}

and the JSON looks like this

{
    "message":"xyz",
    "childMessages":[{"code":"we","message":""},{"code":"uh","message":""},{"code":"wd","message":""}]
}

after fetching the object, code and message for child messages are undefined (not getting populated)

changing json in not in my hand

Please help