// There are 2 documents in collection virus already.
> db.virus.find()

{ "_id" : ObjectId("4c6cf85f1dc3e52659865ff2"), "did" : 1, "recv_time" : 1, "n" : 1 } { "_id" : ObjectId("4c6cf86f1dc3e52659865ff3"), "did" : 1, "recv_time" : 2, "n" : 2 }

// Using shard key and operator in criteria, and using modifier $set in objNew
> db.virus.update({did:1,recv_time:{$gte:3}},{$set:{n:3}},true,false)

// document inserted even recv_time is null
> db.virus.find()

{ "_id" : ObjectId("4c6cf85f1dc3e52659865ff2"), "did" : 1, "recv_time" : 1, "n" : 1 } { "_id" : ObjectId("4c6cf86f1dc3e52659865ff3"), "did" : 1, "recv_time" : 2, "n" : 2 } { "_id" : ObjectId("4c6cf8f55d602a71c933a105"), "did" : 1, "n" : 3 }

// could query with recv_time==null
> db.virus.find(

{recv_time:null}

)

{ "_id" : ObjectId("4c6cf8f55d602a71c933a105"), "did" : 1, "n" : 3 }

// Can't update via ObjectId
> db.virus.update({_id:ObjectId("4c6cf8f55d602a71c933a105")},

{n:4}

)
right object doesn't have full shard key

// Can't update by criteria with shard key
> db.virus.update(

{did:1,recv_time:null}

,

{n:4}

)
shard key must be in update object