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Modeled Responses

Introduction

The result of a performing an operation is what we refer to as a modeled response. Instead of returning the raw XML or JSON data, the SDK will coerce the data into an associative array and normalize some aspects of the data based on its knowledge of the specific service and the underlying response structure.

The actual value returned is a Model (Guzzle\Service\Resource\Model) object. The Model class is a part of the SDK's underlying Guzzle library, but you do not need to know anything about Guzzle to use your operation results. The Model object contains the data from the response and can be used like an array (e.g., $result['Table']). It also has convenience methods like get(), getPath(), and toArray(). The contents of the modeled response depend on the operation that was executed and are documented in the API docs for each operation (e.g., see the Returns section in the API docs for the DynamoDB DescribeTable operation).

$result = $dynamoDbClient->describeTable(array(
    'TableName' => 'YourTableName',
));

// Get a specific value from the result
$table = $result['Table'];
if ($table && isset($table['TableStatus'])) {
    echo $table['TableStatus'];
}
//> ACTIVE

// Get nested values from the result easily
echo $result->getPath('Table/TableStatus');
//> ACTIVE

// Convert the Model to a plain array
var_export($result->toArray());
//> array ( 'Table' => array ( 'AttributeDefinitions' => array ( ... ) ... ) ... )

Working with Model objects

Model objects (and Command objects) inherit from the Guzzle Collection class and implement PHP's native ArrayAccess, IteratorAggregate, and Countable interfaces. This means that they behave like arrays when you are accessing keys and iterating over key-value pairs. You can also use the toArray() method of the Model object to get the array form directly.

However, model objects will not throw errors on undefined keys, so it's safe to use values directly without doing isset() checks. It the key doesn't exist, then the value will be returned as null.

// Use an instance of S3Client to get an object
$result = $s3Client->getObject(array(
    'Bucket' => 'my-bucket',
    'Key'    => 'test.txt'
));

// Using a value that may not exist
if (!$result['ContentLength']) {
    echo "Empty file.";
}

$isDeleted = (bool) $result->get('DeleteMarker');

Of course, you can still use isset() checks if you want to, since Model does implement ArrayAccess. The model object (and underlying Collection object) also has convenience methods for finding and checking for keys and values.

// You can use isset() since the object implements ArrayAccess
if (!isset($result['ContentLength'])) {
    echo "Empty file.";
}

// There is also a method that does the same type of check
if (!$result->hasKey('ContentLength')) {
    echo "Empty file.";
}

// If needed, you can search for a key in a case-insensitive manner
echo $result->keySearch('body');
//> Body
echo $result->keySearch('Body');
//> Body

// You can also list all of the keys in the result
var_export($result->getKeys());
//> array ( 'Body', 'DeleteMarker', 'Expiration', 'ContentLength', ... )

// The getAll() method will return the result data as an array
// You can specify a set of keys to only get a subset of the data
var_export($result->getAll(array('Body', 'ContentLength')));
//> array ( 'Body' => 'Hello!' , 'ContentLength' => 6 )

Getting nested values

The getPath() method of the model is useful for easily getting nested values from a response. The path is specified as a series of keys separated by slashes.

// Perform a RunInstances operation and traverse into the results to get the InstanceId
$result = $ec2Client->runInstances(array(
    'ImageId'      => 'ami-548f13d',
    'MinCount'     => 1,
    'MaxCount'     => 1,
    'InstanceType' => 't1.micro',
));
$instanceId = $result->getPath('Instances/0/InstanceId');

Wildcards are also supported so that you can get extract an array of data. The following example is a modification of the preceding such that multiple InstanceIds can be retrieved.

// Perform a RunInstances operation and get an array of the InstanceIds that were created
$result = $ec2Client->runInstances(array(
    'ImageId'      => 'ami-548f13d',
    'MinCount'     => 3,
    'MaxCount'     => 5,
    'InstanceType' => 't1.micro',
));
$instanceId = $result->getPath('Instances/*/InstanceId');

Using data in the model

Response Models contain the parsed data from the response from a service operation, so the contents of the model will be different depending on which operation you've performed.

The SDK's API docs are the best resource for discovering what the model object will contain for a given operation. The API docs contain a full specification of the data in the response model under the Returns section of the docs for an operation (e.g., S3 GetObject operation, EC2 RunInstances operation).

From within your code you can convert the response model directly into an array using the toArray() method. If you are doing some debugging in your code, you could use toArray() in conjunction with print_r() to print out a simple representation of the response data.

$result = $ec2Client->runInstances(array(/* ... */));
print_r($result->toArray());

You can also examine the service description for a service, which is located in the Resources directory within a given client's namespace directory. For example, here is a snippet from the SQS service description (located in src/Aws/Sqs/Resources/) that shows the schema for the response of the SendMessage operation.

// ...
    'SendMessageResult' => array(
        'type' => 'object',
        'additionalProperties' => true,
        'properties' => array(
            'MD5OfMessageBody' => array(
                'description' => 'An MD5 digest of the non-URL-encoded message body string. This can be used [...]',
                'type' => 'string',
                'location' => 'xml',
            ),
            'MessageId' => array(
                'description' => 'The message ID of the message added to the queue.',
                'type' => 'string',
                'location' => 'xml',
            ),
        ),
    ),
// ...

Getting Response Headers

The Response object is not directly accessible from the Model object. If you are interested in getting header values, the status code, or other data from the response you will need to get the Response object from the Command object (see Command Objects). You may need to switch from using the shorthand command syntax to the expanded syntax so that the command object can be accessed directly.

// Getting the response Model with the shorthand syntax
$result = $s3Client->createBucket(array(/* ... */));

// Getting the response Model with the expanded syntax
$command = $s3Client->getCommand('CreateBucket', array(/* ... */));
$result = $command->getResult();

// Getting the Response object from the Command
$response = $command->getResponse();
$contentLength = $response->getHeader('Content-Length');
$statusCode = $response->getStatusCode();

In some cases, particularly with REST-like services like Amazon S3 and Amazon Glacier, most of the important headers are already included in the response model.