[{"createdByUserId":ObjectId("5e6c2dddad72870c84f8476b"),"dateStart":"1"},{"createdByUserId":ObjectId("5e6c2dddad72870c84f8476a"),"dateStart":"2"}]

db.collection.aggregate([{$match:{$and:[{$expr:{$eq:[{$toObjectId:"5e6c2dddad72870c84f8476b"},"$createdByUserId"]}},{dateStart:{$gte:"1"}}]}}])