docs(samples): Update Datastore snippet for read only transaction

BenWhitehead · BenWhitehead · commit 130a00b99270 · 2019-01-30T15:55:49.000-05:00
* `datastore_transactional_single_entity_group_read_only`
diff --git a/datastore/api/src/functions/concepts.php b/datastore/api/src/functions/concepts.php
@@ -840,7 +840,7 @@ function get_or_create(DatastoreClient $datastore, Entity $task)
 function get_task_list_entities(DatastoreClient $datastore)
 {
     // [START datastore_transactional_single_entity_group_read_only]
-    $transaction = $datastore->transaction();
+    $transaction = $datastore->readOnlyTransaction();
     $taskListKey = $datastore->key('TaskList', 'default');
     $query = $datastore->query()
         ->kind('Task')

Original file line number	Diff line number	Diff line change
`@@ -840,7 +840,7 @@ function get_or_create(DatastoreClient $datastore, Entity $task)`
`840`	`840`	`function get_task_list_entities(DatastoreClient $datastore)`
`841`	`841`	`{`
`842`	`842`	`// [START datastore_transactional_single_entity_group_read_only]`
`843`		`- $transaction = $datastore->transaction();`
	`843`	`+ $transaction = $datastore->readOnlyTransaction();`
`844`	`844`	`$taskListKey = $datastore->key('TaskList', 'default');`
`845`	`845`	`$query = $datastore->query()`
`846`	`846`	`->kind('Task')`