Scanning Tables Using the AWS SDK for PHP Low-Level API

The scan function supports several optional parameters. For example, you can optionally use a scan filter to filter the scan result. In a scan filter you specify a condition and an attribute name on which you want the condition evaluated. For more information about the parameters and the API, see Scan.

The following PHP code scans the ProductCatalog table to find items that are priced less than 0. The sample specifies the following optional parameters:

The following PHP code snippet scans the ProductCatalog table to find all items priced less than 201.

$response = $client->scan(array(
        "TableName" => "ProductCatalog",
        "AttributesToGet" => array("Id"),
        "ScanFilter" => array(
                "Price" => array(
                        "ComparisonOperator" => ComparisonOperator::LT,
                        "AttributeValueList" => array(
                                array( Type::NUMBER => "201" )
                        )
                ),
        )
));

foreach ($response['Items'] as $key => $value) {
   echo "Id: " . $value['Id']['N'] . PHP_EOL;
   echo PHP_EOL;
}

You can also optionally limit the page size, the number of items per page, by adding the optional Limit parameter. Each time you execute the scan function, you get one page of results with a specified number of items. To fetch the next page you execute the scan function again by providing primary key value of the last item in the previous page so the scan function can return the next set of items. You provide this information in the request by setting the ExclusiveStartKey property. Initially this property can be null. For retrieving subsequent pages you must update this property value to the primary key of the last item in the preceding page.

The following PHP code snippet scans the ProductCatalog table. In the request it specifies the Limit and ExclusiveStartKey optional parameters.

$tableName = "ProductCatalog";

# The Scan API is paginated. Issue the Scan request multiple times.
do {
    echo "Scanning table $tableName" . PHP_EOL;
    $request = array(
        "TableName" => $tableName,
        "ScanFilter" => array(
            "Price" => array(
                "ComparisonOperator" => ComparisonOperator::LT,
                "AttributeValueList" => array(
                    array(Type::NUMBER => "201")
                )
            )
        ),
        "Limit" => 2
    );

    # Add the ExclusiveStartKey if we got one back in the previous response
    if(isset($response) && isset($response['LastEvaluatedKey'])) {
        $request['ExclusiveStartKey'] = $response['LastEvaluatedKey'];
    }

    $response = $client->scan($request);

    foreach ($response['Items'] as $key => $value) {
        echo "Id: " . $value['Id'][Type::NUMBER] . PHP_EOL;
        echo "ProductCategory: " . $value['ProductCategory'][Type::STRING] . PHP_EOL;
        echo "Title: " . $value['Title'][Type::STRING] . PHP_EOL;
        echo "Price: " . $value['Price'][Type::NUMBER] . PHP_EOL;
        echo PHP_EOL;
    }

} while(isset($response['LastEvaluatedKey'])); # If there is no LastEvaluatedKey in the response, there are no more items matching this Scan invocation

The following PHP code example prepares sample data to be used by subsequent examples. The program deletes and then re-creates the ProductCatalog table, then loads the table with data.

<?php

require __DIR__ . '/vendor/autoload.php';

use Aws\DynamoDb\DynamoDbClient;
use Aws\DynamoDb\Enum\KeyType;
use Aws\DynamoDb\Enum\Type;

// Instantiate the DynamoDB client with your AWS credentials
$aws = Aws\Common\Aws::factory("./config.php");
$client = $aws->get("dynamodb");

$tableName = "ProductCatalog";

// Delete an old DynamoDB table

echo "Deleting the table...\n";

$result = $client->deleteTable(array(
    "TableName" => $tableName
));

$client->waitUntilTableNotExists(array("TableName" => $tableName));

echo "The table {$tableName} has been deleted.\n";

// Create a new DynamoDB table

echo "# Creating table $tableName..." . PHP_EOL;

$result = $client->createTable(array(
    "TableName" => $tableName,
    "AttributeDefinitions" => array(
        array(
            "AttributeName" => "Id",
            "AttributeType" => Type::NUMBER
        )
    ),
    "KeySchema" => array(
        array(
            "AttributeName" => "Id",
            "KeyType"       => KeyType::HASH
        )
    ),
    "ProvisionedThroughput" => array(
        "ReadCapacityUnits"  => 5,
        "WriteCapacityUnits" => 6
    )
));

$client->waitUntilTableExists(array("TableName" => $tableName));

echo "Table {$tableName} has been created.\n";

// Populate DynamoDB table

echo "# Populating Items to $tableName...\n";

for ($i = 1; $i <= 100; $i++) {
    $response = $client->putItem(array(
        "TableName" => $tableName, 
        "Item" => array(
            "Id"      => array( Type::NUMBER     => $i ), // Primary Key
            "Title"   => array( Type::STRING     => "Book {$i} Title" ),
            "ISBN"    => array( Type::STRING     => "111-1111111111" ),
            "Price"   => array( Type::NUMBER     => 25 ),
            "Authors" => array( Type::STRING_SET => array("Author1", "Author2") )
        )
    ));

    $response = $client->getItem(array(
        "TableName" => "ProductCatalog",
        "Key" => array(
            "Id" => array( Type::NUMBER => $i )
        )
    ));

    echo "Item populated: {$response['Item']['Title']['S']}\n";
    sleep(1);
}

echo "{$tableName} is populated with items.\n";
        

The following PHP code example performs a serial Scan on the ProductCatalog table.

<?php

require __DIR__ . '/vendor/autoload.php';

use Aws\DynamoDb\DynamoDbClient;
use Aws\DynamoDb\Enum\Type;

// Instantiate the DynamoDB client with your AWS credentials
$aws = Aws\Common\Aws::factory("./config.php");
$client = $aws->get("dynamodb");

$tableName = "ProductCatalog";
$params = array(
    "TableName" => $tableName,
    "ScanFilter" => array(
        "Title" => array(
            "AttributeValueList" => array(
                array(Type::STRING => "Book")
            ),
            "ComparisonOperator" => "CONTAINS"
        )
    ),
    "Limit" => 10,
);

// Execute scan operations until the entire table is scanned
$count = 0;
do {
    $response = $client->scan($params);
    $items = $response->get("Items");
    $count = $count + count($items);
    
    // Do something with the $items
    foreach($items as $item) {
        echo "Scanned item with Title \"{$item['Title']['S']}\".\n";
    } 
    
    // Set parameters for next scan
    $params["ExclusiveStartKey"] = $response["LastEvaluatedKey"];
} while ($params["ExclusiveStartKey"]);

echo "{$tableName} table scanned completely. {$count} items found.\n";
        

The following Java code example demonstrates a parallel scan, running multiple Scan requests at the same time. Finally, the program prints a summary of run time statistics.

<?php

require __DIR__ . '/vendor/autoload.php';

use Aws\DynamoDb\DynamoDbClient;
use Aws\DynamoDb\Enum\Type;

// Instantiate the DynamoDB client with your AWS credentials
$aws = Aws\Common\Aws::factory("./config.php");
$client = $aws->get("dynamodb");

$tableName = "ProductCatalog";
$totalSegments = 5;
$params = array(
    "TableName" => $tableName,
    "ScanFilter" => array(
        "Title" => array(
            "AttributeValueList" => array(
                array(Type::STRING => "Book")
            ),
            "ComparisonOperator" => "CONTAINS"
        )
    ),
    "Limit" => 10,
    "TotalSegments" => $totalSegments
);

// Create initial scan commands for each segment
$pendingScanCommands = array();
for ($segment = 0; $segment < $totalSegments; $segment++) {
    $params["Segment"] = $segment;
    $pendingScanCommands[] = $client->getCommand("Scan", $params);
}

// Execute scan operations in parallel until the entire table is scanned
while(count($pendingScanCommands) > 0) {
    // Executes the 5 scan operations in parallel using cURL multi handles
    $completedScanCommands = $client->execute($pendingScanCommands);
    $pendingScanCommands = array();

    // Process results of each scan command
    foreach ($completedScanCommands as $scanCommand) {
        $response = $scanCommand->getResult();
        $segment = $scanCommand->getPath("Segment");
        $items = $response->get("Items");

        // Do something with the items
        foreach($items as $item) {
            echo "Scanned item with Title \"{$item['Title']['S']}\" and Segment \"{$segment}\".\n";
        }

        // If LastEvaluatedKey is present we should continue scanning this segment
        // Otherwise we've reached to end of this segment
        if ($response["LastEvaluatedKey"]) {
            echo "LastEvaluatedKey found creating new scan command for Segment: {$segment}.\n";
            $params["Segment"] = $segment;
            $params["ExclusiveStartKey"] = $response["LastEvaluatedKey"];
            $pendingScanCommands[] = $client->getCommand("Scan", $params);
        } else {
            echo "Segment: {$segment} scanned completely!\n";
        }
    }
}

echo "Table {$tableName} scanned completely.\n";