mongodb findandmodify

1const READ_DOCUMENTATION ; 
2https://docs.mongodb.com/manual/reference/command/findAndModify/#lasterrorobject
3
4The lastErrorObject embedded document contains the following fields:
5updatedExisting boolean
6  true if an update operation modified an existing document.
7upserted document
8	Contains the ObjectId of the inserted document if an update operation with upsert: true resulted in a new document.
9Value
10	For remove operations, value contains the removed document if the query matches a document. If the query does not match a document to remove, value contains null.
11
12	For update operations, the value embedded document contains the following:
13
14	If the new parameter is not set or is false:
15
16    the pre-modification document if the query matches a document;
17    otherwise, null.
18    If new is true:
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20    the modified document if the query returns a match;
21    the inserted document if upsert: true and no document matches the query;
22    otherwise, null.
23