ConditionExpression attribute_not_exists()

Question

I tried using ConditionExpression when inserting items in the database but it doesn't work, the php script breaks when the Putitem() function runs.

If the item does not exist, I want to insert the item.

$response = $client->putItem(array(
    'TableName' => 'tablename',
    'Item' => array(
        'serialNumber'   => array('S' => 'test123'),
        'deviceType' => array('S' => '1')
    ),
    'ConditionExpression' => 'attribute_not_exists(serialNumber)'
));

I tried var_dump $response but the code breaks on the function above.

serialNumber It is a partition key and should work as expected.

The code below works fine, but he replaces the existing items with new values, which is what I don't want to happen.

$response = $client->putItem(array(
    'TableName' => 'tablename',
    'Item' => array(
        'serialNumber'   => array('S' => 'test123'),
        'deviceType' => array('S' => '1')
    )
));

Answer 1

When the condition you set evaluates to false, you are expected to return a CondidtionCheckFailedException. Try wrapping the code in a try/catch block and see if it works as expected?

try {
$response = $client->putItem(array(
    'TableName' => 'tablename',
    'Item' => array(
        'serialNumber'   => array('S' => 'test123'),
        'deviceType' => array('S' => '1')
    )
));
}
catch(Exception $e) {
  echo $e->getMessage();
}