db={"records":[{"ItemReport":[{"WorkDoneBy":[{"CompletedHours":11,"DateCompleted":ISODate("2017-09-29T04:00:00Z"),"Person":ObjectId("5dcb6409e63830b7aa54fd6e")},{"CompletedHours":36,"DateCompleted":ISODate("2018-05-18T04:00:00Z"),"Person":ObjectId("5dcb6409e63830b7aa54fd6e")},{"CompletedHours":32,"DateCompleted":ISODate("2018-05-18T04:00:00Z"),"Person":ObjectId("5dcb6409e63830b7aa54fd6e")}]}],"RecordID":9018,"RecordType":"Item","Status":"Done"},{"ItemReport":[{"WorkDoneBy":[{"CompletedHours":1.5,"DateCompleted":ISODate("2017-09-01T04:00:00Z"),"Person":ObjectId("5dcb6409e63830b7aa54fe5f")}]}],"RecordID":9019,"RecordType":"Item","Status":"Done"},{"ItemReport":[{"WorkDoneBy":[{"CompletedHours":2,"DateCompleted":ISODate("2017-09-08T04:00:00Z"),"Person":ObjectId("5dcb6409e63830b7aa54fd6e")},{"CompletedHours":18,"DateCompleted":ISODate("2017-09-15T04:00:00Z"),"Person":ObjectId("5dcb6409e63830b7aa54fd6e")},{"CompletedHours":7,"DateCompleted":ISODate("2017-09-20T04:00:00Z"),"Person":ObjectId("5dcb6409e63830b7aa54fd6e")}]}],"RecordID":9017,"RecordType":"Item","Status":"Done"},{"ItemReport":[{"WorkDoneBy":[{"CompletedHours":1.5,"DateCompleted":ISODate("2015-09-01T04:00:00Z"),"Person":ObjectId("5dcb6409e63830b7aa54fe5f")}]}],"RecordID":9019,"RecordType":"Item","Status":"Done"}],"people":[{_id:ObjectId("5dcb6409e63830b7aa54fe5f"),DisplayName:"Joe Jones"},{_id:ObjectId("5dcb6409e63830b7aa54fd6e"),DisplayName:"Alice Smith"}]}

db.records.aggregate([{"$project":{"ItemReport":{$map:{input:"$ItemReport",as:"ir",in:{WorkDoneBy:{$filter:{input:"$$ir.WorkDoneBy",as:"value",cond:{"$and":[{"$ne":["$$value.DateCompleted",null]},{"$gt":["$$value.DateCompleted",new Date("2017-01-01T12:00:00.000Z")]},{"$lt":["$$value.DateCompleted",new Date("2018-12-31T12:00:00.000Z")]}]}}}}}}}},{"$match":{$expr:{$anyElementTrue:{$map:{input:"$ItemReport",in:{$gt:[{$size:"$$this.WorkDoneBy"},0]}}}}}},{$addFields:{peopleIds:{$reduce:{input:"$ItemReport",initialValue:[],in:{$setUnion:["$$value","$$this.WorkDoneBy.Person"]}}}}},{$lookup:{from:"people",localField:"peopleIds",foreignField:"_id",as:"people"}},{$project:{_id:1,ItemReport:{$map:{input:"$ItemReport",as:"ir",in:{WorkDoneBy:{$map:{input:"$$ir.WorkDoneBy",as:"wdb",in:{$mergeObjects:["$$wdb",{Person:{$arrayElemAt:[{$filter:{input:"$people",cond:{$eq:["$$this._id","$$wdb.Person"]}}},0]}}]}}}}}}}}])