[{"_id":"12345","to":"fnk34""messages":[{id:"1",title:"hello",body:"body"createdAt:123},{id:"2",title:"hello",body:"body"createdAt:3},{id:"3",title:"hello",body:"body"createdAt:13},]},]

db.collection.findOneAndUpdate({to:"fnk34"},{$push:{messages:{'$each':[message],'$sort':{'message.createdAt':-1}}}},{upsert:true})