mongodb: extract timestamp from ObjectID in json query

You can do this fairly simply, at doc page Mongo Extended JSON (which is quite well hidden) you can find a table describing how to represent mongo extended datatypes in JSON. As you probably know, the first 4 bytes of ObjectId represent the timestamp, this maps directly to 8 first characters in the hex string. Thus, the following should work:

jhonkola@ubuntu:~$ mongoexport -d so_test -c example -q '{"_id" : {"$gt" : {"$oid" : "4fad36290000000000000000"}}}'connected to: 127.0.0.1{ "_id" : { "$oid" : "4fad3629a8bbba98829d5c1e" }, "a" : "bar", "b" : 2 }{ "_id" : { "$oid" : "4fad362ea8bbba98829d5c1f" }, "a" : "baz", "b" : 3 }{ "_id" : { "$oid" : "4fad3635a8bbba98829d5c20" }, "a" : "buzz", "b" : 4 }{ "_id" : { "$oid" : "4fad363ca8bbba98829d5c21" }, "a" : "fizz", "b" : 5 }exported 4 recordsjhonkola@ubuntu:~$ 

Below are all the commands used for the example for reference.

> use so_testswitched to db so_test> db.example.insert({a: "foo", b: 1})> db.example.insert({a: "bar", b: 2})> db.example.insert({a: "baz", b: 3})> db.example.insert({a: "buzz", b: 4})> db.example.insert({a: "fizz", b: 5})> db.example.find(){ "_id" : ObjectId("4fad3620a8bbba98829d5c1d"), "a" : "foo", "b" : 1 }{ "_id" : ObjectId("4fad3629a8bbba98829d5c1e"), "a" : "bar", "b" : 2 }{ "_id" : ObjectId("4fad362ea8bbba98829d5c1f"), "a" : "baz", "b" : 3 }{ "_id" : ObjectId("4fad3635a8bbba98829d5c20"), "a" : "buzz", "b" : 4 }{ "_id" : ObjectId("4fad363ca8bbba98829d5c21"), "a" : "fizz", "b" : 5 }> db.example.find({_id : {$gt : ObjectId("4fad362e0000000000000000")}}){ "_id" : ObjectId("4fad362ea8bbba98829d5c1f"), "a" : "baz", "b" : 3 }{ "_id" : ObjectId("4fad3635a8bbba98829d5c20"), "a" : "buzz", "b" : 4 }{ "_id" : ObjectId("4fad363ca8bbba98829d5c21"), "a" : "fizz", "b" : 5 }> byejhonkola@ubuntu:~$ mongodump -d so_test -c example -q '{"_id" : {"$gt" : {"$oid" : "4fad36290000000000000000"}}}'connected to: 127.0.0.1DATABASE: so_test    to     dump/so_test    so_test.example to dump/so_test/example.bson         4 objectsjhonkola@ubuntu:~$ mongoexport -d so_test -c example -q '{"_id" : {"$gt" : {"$oid" : "4fad36290000000000000000"}}}'connected to: 127.0.0.1{ "_id" : { "$oid" : "4fad3629a8bbba98829d5c1e" }, "a" : "bar", "b" : 2 }{ "_id" : { "$oid" : "4fad362ea8bbba98829d5c1f" }, "a" : "baz", "b" : 3 }{ "_id" : { "$oid" : "4fad3635a8bbba98829d5c20" }, "a" : "buzz", "b" : 4 }{ "_id" : { "$oid" : "4fad363ca8bbba98829d5c21" }, "a" : "fizz", "b" : 5 }exported 4 records