Firebase REST API - Guzzle PATCH request is deleting data

Question

According to the firebase docs, https://www.firebase.com/docs/rest-api.html, it states:

PATCH - Updating Data
You can update specific children at a location without overwriting existing data 
with a PATCH request. Named children in the data being written with PATCH will be 
written, but omitted children will not be deleted. This is equivalent to the 
update( ) function.

curl -X PATCH -d '{"last":"Jones"}' \
 https://SampleChat.firebaseIO-demo.com/users/jack/name/.json
A successful request will be indicated by a 200 OK HTTP status code. 
The response will contain the data written:

{"last":"Jones"}

Now my understanding of this, is that if I wish to update only parts of a resource, then I can use a PATCH request.

My simplified firebase database is as follows:

  "exchange-rates" : {
    "eur" : {
      "fx" : 1.2,
      "currency_symbol" : "€",
      "updated_at" : "2014-06-13T22:49:23+0100",
    },
    "usd" : {
      "fx" : 1.6,
      "currency_symbol" : "$",
      "updated_at" : "2014-06-13T22:49:23+0100",
    },
    "gbp" : {
      "fx" : 1,
      "currency_symbol" : "£",
      "updated_at" : "2014-06-16T15:43:15+0100",
    }
  }

However If I omit the currency_symbol and updated_at from the payload in my patch request, then Firebase removes these attributes from the database.

    $auth = 'SUPER_SECRET_CODE';
    $guzzleClient = new GuzzleHttp\Client();
    $url = https://DATABASE.firebaseio.com/.json;


    $data['exchange-rates']['gbp']['fx'] = (float) 1;
    $data['exchange-rates']['usd']['fx'] = (float) 1.66;
    $data['exchange-rates']['eur']['fx'] = (float) 1.22;

    $payload =
        [
            'query' => [ 'auth' => $auth ],
            'json' => $data
        ];

    $response = $guzzleClient->patch($url, $payload);

As such, the PATCH request is not working as it should, or I have misunderstood what Firebase should do with this PATCH request - or I am missing something. Any thoughts?

Also, If I wish to add an object to the exchange-rates object, I should be able to do so.

$data['exchange-rates']['chf']['fx'] = 2.13;

    $payload =
        [
            'query' => [ 'auth' => $auth ],
            'json' => $data
        ];

    $response = $guzzleClient->patch($url, $payload);

However all this does is just overwrite all the existing exchange-rates, and now I only have 1 exchange rate in the db.

Answer 1

The update/PATCH operations are not recursive. They only observe keys for the direct children of your update. Example:

// assume data:  { foo: 'bar', baz: {uno: 1, dos: 2}, zeta: {hello: 'world'} };

curl -X PATCH -d  '{"tres": 3}' $URL

// baz is now: {uno: 1, dos: 2, tres: 3}

curl -X PATCH -d '{"foo": "barr", baz: {"tres": 3}}' $URL

// baz is now {tres: 3}

So the update is only one level deep. If one of the child records you provide is an object, it replaces the child at that path rather than trying to merge the two.