Definition
Return Values
A map of IDs (i.e. _id field values) for documents that were upserted by all
update and replace operations in the bulk write.
The index of each ID in the map corresponds to each document's position in the
bulk operation. If a document had an ID prior to upserting (i.e. the server did
not generate an ID), the index will contain its _id field value. Any
server-generated ID will be a MongoDB\BSON\ObjectId instance.
Errors/Exceptions
MongoDB\Exception\BadMethodCallException if this method is
called and the write operation used an unacknowledged write concern.