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$returnKeyNote
Deprecated since v3.2
Starting in v3.2, the
$returnKeyoperator is deprecated in themongoshell. In themongoshell, usecursor.returnKey()instead.Only return the index field or fields for the results of the query. If
$returnKeyis set totrueand the query does not use an index to perform the read operation, the returned documents will not contain any fields. Use one of the following forms:db.collection.find( { <query> } )._addSpecial( "$returnKey", true ) db.collection.find( { $query: { <query> }, $returnKey: true } )