How can I fetch all items from a DynamoDB table without specifying the primary key?

Question

I have a table called products with primary key Id. I want to select all items in the table. This is the code is I'm using:

$batch_get_response = $dynamodb->batch_get_item(array(     'RequestItems' => array(          'products' => array(             'Keys' => array(                 array( // Key #1                     'HashKeyElement'  => array( AmazonDynamoDB::TYPE_NUMBER => '1'),                     'RangeKeyElement' => array( AmazonDynamoDB::TYPE_NUMBER => $current_time),                 ),                 array( // Key #2                     'HashKeyElement'  => array( AmazonDynamoDB::TYPE_NUMBER => '2'),                     'RangeKeyElement' => array( AmazonDynamoDB::TYPE_NUMBER => $current_time),                 ),             )         )     )    )); 

Is it possible to select all items without specifying the primary key? I'm using the AWS SDK for PHP.

Answer 1

Amazon DynamoDB provides the Scan operation for this purpose, which returns one or more items and its attributes by performing a full scan of a table. Please be aware of the following two constraints:

• Depending on your table size, you may need to use pagination to retrieve the entire result set:

  Note
  If the total number of scanned items exceeds the 1MB limit, the scan stops and results are returned to the user with a LastEvaluatedKey to continue the scan in a subsequent operation. The results also include the number of items exceeding the limit. A scan can result in no table data meeting the filter criteria.

  The result set is eventually consistent.

• The Scan operation is potentially costly regarding both performance and consumed capacity units (i.e. price), see section Scan and Query Performance in Query and Scan in Amazon DynamoDB:

  [...] Also, as a table grows, the scan operation slows. The scan operation examines every item for the requested values, and can use up the provisioned throughput for a large table in a single operation. For quicker response times, design your tables in a way that can use the Query, Get, or BatchGetItem APIs, instead. Or, design your application to use scan operations in a way that minimizes the impact on your table's request rate. For more information, see Provisioned Throughput Guidelines in Amazon DynamoDB. [emphasis mine]

You can find more details about this operation and some example snippets in Scanning Tables Using the AWS SDK for PHP Low-Level API for Amazon DynamoDB, with the most simple example illustrating the operation being:

$dynamodb = new AmazonDynamoDB();  $scan_response = $dynamodb->scan(array(     'TableName' => 'ProductCatalog'  ));  foreach ($scan_response->body->Items as $item) {     echo "<p><strong>Item Number:</strong>"          . (string) $item->Id->{AmazonDynamoDB::TYPE_NUMBER};     echo "<br><strong>Item Name: </strong>"          . (string) $item->Title->{AmazonDynamoDB::TYPE_STRING} ."</p>"; }