Group Mongo documents by id and get the latest document by timestamp

Question

Imagine we have the following set of documents stored in mongodb:

{ \"fooId\" : \"1\", \"status\" : \"A\", \"timestamp\" : ISODate(\"2016-01-01T00:00:00.000Z         


        

Answer 1

If you are doing and aggregation, you need to do similar to SQL , which mean specify the aggregation operation per column, the only option you have is use the $$ROOT operator

db.test.aggregate(
   [
    { $sort: { timestamp: 1 } },
     {
       $group:
         {
           _id: "$fooId",
           timestamp: { $last: "$$ROOT" }
         }
     }
   ]
);

But that will change the output a little bit

{ "_id" : "1", "timestamp" : { "_id" : ObjectId("570e6be3e81c8b195818e7fa"), 
  "fooId" : "1", "status" : "A", "timestamp" :ISODate("2016-01-01T00:00:00Z"), 
  "otherInfo" : "BAR" } }

If you want to return the original document format, you probably need a $project stage after that