add json parameter to the scroll function

Author: ShisunXia

README.md

@@ -987,7 +987,7 @@ The package is developed and tested under Elasticsearch ``v6.*``. It should be a
    |:--------:|:--------:|:-----------------------:|:---------:|:-----------------------------------------------------:|
    |scroll_alive|          | ``string``             |``5m``    | This specifies the life span of the scroll session.   |
    |scroll_size|          | ``integer``             |``500``   | This specifies the number of records retrieved from Elasticsearch per batch.|
-   
+   |json      |          | ``boolean``             |``false``   | If encode the results from each batch in JSON format. Fetching data and put the data in PHP array can consume a lot of memory. This option can greatly reduce the memory usage.|
 * Output
    
    ``array``

src/LaravelElasticsearchQueryBuilder.php

@@ -748,7 +748,7 @@ public function get() {
 		return $this;
 	}
 
-	public function scroll($scroll_alive = '5m', $scroll_size = 500) {
+	public function scroll($scroll_alive = '5m', $scroll_size = 500, $json = false) {
 		$this->scroll_alive = $scroll_alive;
 		$this->scroll_size = $scroll_size;
 		$scroll_id = $this->get()->rawResults()['_scroll_id'];
@@ -760,9 +760,13 @@ public function scroll($scroll_alive = '5m', $scroll_size = 500) {
 				]
 			);
 			if (count($response['hits']['hits']) > 0) {
-				array_map(function ($value) use (&$results) {
-					$results[] = $value['_source'];
-				}, $response['hits']['hits']);
+				if($json) {
+					$results[] = json_encode(array_column($response['hits']['hits'], '_source'));
+				} else {
+					array_map(function ($value) use (&$results) {
+						$results[] = $value['_source'];
+					}, $response['hits']['hits']);
+				}
 				$scroll_id = $response['_scroll_id'];
 			} else {
 				break;