Given this aggregation: db.inventory.drop() db.inventory.insertOne( { item: 1, qty:{ sold: 1 } }); db.inventory.insertOne( { item: 3, qty:{ etc: 3 } }); db.inventory.insertOne( { item: 4, }); var pipeline = [{ $project : { "_id" : 0, "0" : { "sold" : "$qty.sold" } } }]; var result = db.inventory.aggregate(pipeline); result.forEach( function (r) { printjson(r) } ) If you run the above aggregation against 3.2.* this is the result: { "0" : { "sold" : 1 } } { } { } If you run the above aggregation against 3.4.* this is the result: { "0" : { "sold" : 1 } } { "0" : { } } { "0" : { } }