Inserting unique value into DynamoDB list.

gistfile1.txt

  $marshaler = new Marshaler();

        $UpdateExpression = "
		SET #subscribers = list_append(if_not_exists(#subscribers, :empty_list), :subscriber)
	";

    	$ConditionExpression = "
		 NOT contains (#subscribers,:subscriberStr)
	";

        $ExpressionAttributeNames = [
		"#subscribers" => "subscribers"
	];


	$ExpressionAttributeValues = $marshaler->marshalJson('
		{
			":subscriber" : ['.$subscriber.'],
			":subscriberStr" : '.$subscriber.',
			":empty_list" :[]
		}
	');


	$tableName = 'publisherRelationships';

        $key = $marshaler->marshalJson('
                {
			"publisher": '.$publisher.'
                }
       ');

        $params = [
                'TableName' => $tableName,
    		'Key' => $key,
		'UpdateExpression' => $UpdateExpression,
		'ConditionExpression' => $ConditionExpression,
		'ExpressionAttributeNames' => $ExpressionAttributeNames,
		'ExpressionAttributeValues' => $ExpressionAttributeValues
        ];