发布于 2015-09-14 15:17:30 | 83 次阅读 | 评论: 0 | 来源: 网络整理
Only return the index key or keys for the results of the query. If $returnKey is set to true and the query does not use an index to perform the read operation, the returned documents will not contain any fields. Use one of the following forms:
db.collection.find( { <query> } )._addSpecial( "$returnKey", true )
db.collection.find( { $query: { <query> }, $returnKey: true } )