db.ttl.insert( { _id: 12, type: "misc", item: "card", qty: 15, "createAt": new Date(Date.now()), "expireAt": new Date(Date.now()) } )
db.ttl.insert( { _id: 12, type: "misc", item: "card", qty: 15, "expireAt": new Date(Date.now()) } )
db.ttl.update({},{ "$set" : { "expireAt": new Date(Date.now()) }}, false, true)
db.ttl.createIndex({"createAt":1}, {expireAfterSeconds:20})