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  1. PHP Driver: Library
  2. PHPLIB-327

ChangeStream::next() should not increment key for the first event

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    • Type: Icon: Bug Bug
    • Resolution: Fixed
    • Priority: Icon: Minor - P4 Minor - P4
    • 1.3.1
    • Affects Version/s: 1.3.0
    • Component/s: None
    • Labels:
      None

      Given the following script to iterate a change stream:

      $collection = (new MongoDB\Client($uri))->test->inventory;
$collection->drop();

$changeStream = $collection->watch();

for ($changeStream->rewind(); true; $changeStream->next()) {
    if ( ! $changeStream->valid()) {
        continue;
    }

    $event = $changeStream->current();

    printf("%d: %s\n", $changeStream->key(), $event['operationType']);
}

      And a second script to populate it with some events:

      $collection = (new MongoDB\Client($uri))->test->inventory;

$result = $collection->insertOne(['name' => 'Widget', 'quantity' => 5]);
$collection->updateOne(['_id' => $result->getInsertedId()], ['$inc' => ['quantity' => -1]]);
$collection->deleteOne(['_id' => $result->getInsertedId()]);

      I would expect the following output from the first script:

      0: insert
1: update
2: delete

      However, the key of the first "insert" starts at 1. This is likely due to ChangeStream::next() always incrementing the key counter. We might need to make a special allowance to only increment when we're advancing from a previous element.

      Note: if the second script were executed between the call to Collection::watch() and ChangeStream::rewind(), the first key would be 0 as expected.

            Assignee:
            katherine.walker@mongodb.com Katherine Walker (Inactive)
            Reporter:
            jmikola@mongodb.com Jeremy Mikola
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              Created:
              Updated:
              Resolved: