node.js - Aggregate: return document with no subdocument OR with latest subdocument only -


this more complex version of the query in question

i've got these mongoose schemas: 

var thread = new schema({     title: string, messages: [message] }); var message = new schema({     date_added: date, author: string, text: string });

how return threads latest message subdocument (limit 1) , threads without message subdocuments well?


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