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

Though there is no direct way to bring back original documents and I don't see any value, but try following aggregation query:

db.collection.aggregate([
   {$sort: {fooId:1, timestamp: -1}},
   {$group:{_id:"$fooId", doc:{$first:"$$ROOT"}}},
   {$project:{_id:0, doc:["$doc"]}}
]).forEach(function(item){

  printjson(item.doc[0]);

});

This query will emit:

{ 
    "_id" : ObjectId("570e76d5e94e6584078f02c4"), 
    "fooId" : "2", 
    "status" : "B", 
    "timestamp" : ISODate("2016-01-02T00:00:00.000+0000"), 
    "otherInfo" : "BAR"
}
{ 
    "_id" : ObjectId("570e76d5e94e6584078f02c8"), 
    "fooId" : "3", 
    "status" : "D", 
    "timestamp" : ISODate("2016-01-04T00:00:00.000+0000"), 
    "otherInfo" : "BAR"
}
{ 
    "_id" : ObjectId("570e76d5e94e6584078f02c2"), 
    "fooId" : "1", 
    "status" : "C", 
    "timestamp" : ISODate("2016-01-03T00:00:00.000+0000"), 
    "otherInfo" : "BAR"
}