Id is Returning 0 for Rest API with Go

I have been trying to build some simple backend REST API using Go using the Google App Engine and its datastore and AngularJS on the frontend. I was able to get everything working but the edit. And I am not sure why the JSON is not un-marshaling correctly.

Struct:

type Article struct {
    Key    int64    `json:"Key" datastore:"-"`
    Title  string
    Text   string   `datastore:",noindex"`
    Author string
    Tags   string
    Posted time.Time
}

When I load the article, I populate the Key property with the id value from the datastore. Example: 5593215650496512

I keep that field in a hidden input on my form, and submit the form's content as JSON through an HTTP Post to the Go backend.

Before the submit, I can see that the Key holds the proper value. Here is the form though:

                <form name="articleForm" ng-submit="saveArticle(article)">
                    <fieldset>
                        <input type="hidden" name="key" ng-value="article.Key" />
                        <div class="form-group">
                            <input class="form-control" ng-model="article.Title" placeholder="Title" name="title" type="text" required autofocus />
                            <div class="alert alert-danger" ng-show="articleForm.Title.$invalid && articleForm.Title.$dirty">
                                <ul>
                                    <li ng-show="articleForm.title.$error.required">this field is required</li>
                                </ul>
                            </div>
                        </div>
                        <div class="form-group">
                            <wysiwyg 
                                name="text"
                                textarea-id="articleText" 
                                textarea-class="form-control"  
                                textarea-height="180px" 
                                textarea-name="articleText"
                                ng-model="article.Text" 
                                enable-bootstrap-title="true" 
                                textarea-required>
                            </wysiwyg>
                            <div class="alert alert-danger" ng-show="articleForm.text.$invalid && articleForm.text.$dirty">
                                <ul>
                                    <li ng-show="articleForm.text.$error.required">this field is required</li>
                                </ul>
                            </div>
                        </div>
                        <div class="form-group">
                            <tags-input ng-model="tags"></tags-input>
                        </div>
                        <button type="submit" ng-disabled="!articleForm.$valid" class="btn btn-primary">
                            Save Article
                        </button>
                    </fieldset>
                </form>

The $scope.article object right before the http post:

> Author: "Matt Ridley"
Key: "5593215650496512"
Posted: "2015-06-29T12:57:20.833525Z"
Tags: "test,so-cool"
Text: "<div>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer nec odio. Praesent libero. Sed cursus ante dapibus diam. Sed nisi. Nulla quis sem at nibh elementum imperdiet. Duis sagittis ipsum. Praesent mauris. Fusce nec tellus sed augue semper porta. Mauris massa. Vestibulum lacinia arcu eget nulla.&nbsp;</div>"
Title: "Example Article 8"

However, the Key property remains 0. I am able to pass that value in as a single id value with no issue for delete and load.

Code for loading just the id (this was the load version, it works):

var id int64
json.Unmarshal(body, &id)
c.Infof("ID: %v", id)

key := datastore.NewKey(c, "Article", "", id, nil)

Code for the edit with additional values (does not work, id = 0):

var article Article
json.Unmarshal(body, &article)
c.Infof("Article:%g", article)
c.Infof("Body:" + string(body))
c.Infof("Key:%v", article.Key)
article.Posted = time.Now()

Here is a dump of the struct after json.Unmarshal:

> 2015/06/29 03:04:08 INFO: Article:{%!g(int64=0) %!g(string=Example Article 8)
> %!g(string=<div>Lorem ipsum dolor sit amet, consectetur adipiscing
> elit. Integer nec odio. Praesent libero. Sed cursus ante dapibus diam.
> Sed nisi. Nulla quis sem at nibh elementum imperdiet. Duis sagittis
> ipsum. Praesent mauris. Fusce nec tellus sed augue semper porta.
> Mauris massa. Vestibulum lacinia arcu eget
> nulla.&nbsp;</div>) %!g(string=Matt Ridley)
> %!g(string=test,so-cool) {%!g(int64=63570890170) %!g(int32=842211000)
> %!g(*time.Location=&{UTC [] [] 0 0 <nil>})}}

Key is logging as...

> 2015/06/29 03:04:08 INFO: Key:0

The body dump:

> 2015/06/29 14:00:34 INFO: Body:{"Key":"5593215650496512","Title":"Example Article 8","Text":"<div>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer nec odio. Praesent libero. Sed cursus ante dapibus diam. Sed nisi. Nulla quis sem at nibh elementum imperdiet. Duis sagittis ipsum. Praesent mauris. Fusce nec tellus sed augue semper porta. Mauris massa. Vestibulum lacinia arcu eget nulla.&nbsp;</div>","Author":"Matt Ridley","Tags":"test,so-cool","Posted":"2015-06-29T13:28:06.168062Z"}

I have been banging my head on this for a few days, so any insight would be appreciated. Thanks!

You're ignoring the error when you Unmarshal into your Article. You should see json: cannot unmarshal string into Go value of type int64, because the Key value in the body is being formatted as a string.

If it is what you expect, then you can tell the json package to make use of it by adding the string option to the tag:

type Article struct {
    Key    int64    `json:"Key,string" datastore:"-"`
    Title  string
    Text   string   `datastore:",noindex"`
    Author string
    Tags   string
    Posted time.Time
}