DyanmoDB: not getting the answer I'm expecting using batch_get_item - php

Question

I am trying to do a batch_get_item to request multiple items from a table. I am following the PHP example in the DynamoDB documentation, but I am not getting the results I'm expecting.
Following is the code:
$batch_array = array ();
$batch_array[]= array ('HashKeyElement' =>
array( AmazonDynamoDB::TYPE_STRING => 'V1L3M5O5L1W8R5B6D2Q1S8V0B3R8M7A6R0X0'));
$options = array (
'RequestItems' => array(
'profile_dev' => array (
'Keys' => $batch_array
)
)
);
$result = $this->db->batch_get_item($options);
Instead of getting the data, I am getting a very long response, and I'm including the relevant information from the tail end of it:
[x-aws-body] => {"RequestItems":{"profile_dev":{"Keys":[{"HashKeyElement":{"S":"V1L3M5O5L1W8R5B6D2Q1S8V0B3R8M7A6R0X0"}}]}}} ) [body] => CFSimpleXML Object ( [__type] => com.amazon.coral.validate#ValidationException [message] => One or more parameter values were invalid: The provided key size does not match with that of the schema ) [status] => 400 ) )
The hashKey for this table is a string. It has a rangeKey, but I am using the hashKey so I can get all the rows matching the hashKey. What am I missing?

Answer 1

The DynamoDB documentation (and SDK samples) have colossal bugs in them. The documentation, and actual SDK code, make use only of the hashKeyElement, but in fact if a table has both a hashKey AND a rangeKey, both must be used.
When I used both the hashKey and the rangeKey, the call worked.

Answer 2

Get (or batch get) requires you to completely define the key of all items you are getting. If you want to retrieve all rows with the same hashKey using a single call, it seems like you're looking for Query.

Answer 3

You don't need to use BatchGet, you should be using Query. Here is an example using the PHP SDK to get all items with the HASH key 'YourHashKey' on table 'YourTable'
// Instantiate the class
$dynamodb = new AmazonDynamoDB();
$response = $dynamodb->query(array(
'TableName' => 'YourTable',
'HashKeyValue' => array( AmazonDynamoDB::TYPE_STRING => 'YourHashKey' ),
));
Reference: http://docs.amazonwebservices.com/amazondynamodb/latest/developerguide/LowLevelPHPQuerying.html