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GET Representation != POST Representation

GET Representation != POST Representation

So far, the representation of a programmer that we send in our PUT request exactly matches the representation the server sends in the response after a GET request. But it does’t need to be this way.

When we POST or PUT to a programmer URI, we send data that contains an avatarNumber field. But imagine if we designed the API so that when we GET a programmer, the representation in the response contains an avatarUrl instead of avatarNumber. In this world, the representation we send in a request would be different than the representation that the server sends back in a response. And this would be perfectly ok!

The point is that I don’t want you to feel like the data your API receives needs to look exactly like the data you send back. Nope. Both are just representations of a resource.

With that said, if you make the representations inconsistent for no reason, your API users will hunt you down with pitchforks. So if you expect avatarNumber in the POST body, don’t send back avatar_number in the GET request. That’s just mean.

Immutable Properties

In our API, the programmer’s nickname is its unique, primary key. So, I don’t really want it to be editable. In other words, even though the response representation of a programmer resource will contain a nickname property, a PUT request to update it should not have this field.

Let’s first add to our scenario to test that even if we send a nickname field, the resource’s nickname doesn’t change:

# features/api/programmer.feature
# ...

Scenario: PUT to update a programmer
  # ...
  And I have the payload:
    """
    {
      "nickname": "CowgirlCoder",
      "avatarNumber" : 2,
      "tagLine": "foo"
    }
    """
  # ...
  But the "nickname" property should equal "CowboyCoder"

Run the test first to make sure it’s failing. Next, let’s update the handleRequest function to only set the nickname on a new Programmer:

private function handleRequest(Request $request, Programmer $programmer)
{
    $data = json_decode($request->getContent(), true);
    $isNew = !$programmer->id;

    if ($data === null) {
        throw new \Exception(sprintf('Invalid JSON: '.$request->getContent()));
    }

    // determine which properties should be changeable on this request
    $apiProperties = array('avatarNumber', 'tagLine');
    if ($isNew) {
        $apiProperties[] = 'nickname';
    }

    // ...
}

Now run the test:

$ php vendir/bin/behat

Perfect! We’ve decided just to ignore these “extra” properties. You could also decide to return an error response instead. It just depends on your taste. What we did here is easier to use, but our client may also not notice that we’re ignoring some of the submitted data. We’ll talk about error responses in a few minutes.

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