mongoexport --host mongodb1.example.net --port 37017 --username user --password pass --collection contacts --db marketing --out mdb1-examplenet.json

mongoimport --host mongodb1.example.net --port 37017 --username user --password pass --collection contacts --db marketing --file /opt/backups/mdb1-examplenet.json

db.collection.find({lang:"zh",createtime:{$gte:new Date("3/31/2015 6:52:46")}});

{"liju":{$ne:null},"liju.mediaid":{$ne:null}};

db.collection.find().sort( { age: -1 } )-1为降序，1为正序

db.collection.find( { $query: {}, $orderby: { age : -1 } } )

var bulk = db.items.initializeUnorderedBulkOp();

bulk.find( { status: "D" } ).update( { $set: { status: "I", points: "0" } } );

bulk.find( { item: null } ).update( { $set: { item: "TBD" } } );

bulk.execute();