When using db.getLastErrorObj(), clients must issue the db.getLastErrorObj() on the same connection as the write operation they wish to confirm.
Changed in version 2.6: A new protocol for write operations integrates write concerns with the write operations, eliminating the need for a separate db.getLastErrorObj(). Most write methods now return the status of the write operation, including error information. In previous versions, clients typically used the db.getLastErrorObj() in combination with a write operation to verify that the write succeeded.
The db.getLastErrorObj() can accept the following parameters:
Parameter Type Description key int or string Optional. The write concern’s w value. wtimeout int Optional. The time limit in milliseconds.
The returned document provides error information on the previous write operation.
If the db.getLastErrorObj() method itself encounters an error, such as an incorrect write concern value, the db.getLastErrorObj() throws an exception.
For information on the returned document, see getLastError command.