MongoDB的：从对象ID在JSON查询

Question

提取物戳我想用一个JSON查询提取从我的对象ID时间戳，因为我想用mongodump但只有某些转储日期之间的数据。我不想把我的时间戳放在ObjectID以外的地方，因为我需要数据库尽可能小。

是否有向exstract从对象ID时间戳与mongodump接受一个简单的JSON查询的方法吗？

Answer 1

你可以很简单地做到这一点，在文档页Mongo Extended JSON（这是很好的隐藏），你可以找到一张表，描述如何用JSON表示mongo扩展数据类型。您可能知道，ObjectId的前4个字节表示时间戳，它直接映射到十六进制字符串中的8个第一个字符。因此，以下应该工作：

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 records 
jhonkola@ubuntu:~$ 

以下是用于示例供参考的所有命令。

> use so_test 
switched 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 } 
> 
bye 

jhonkola@ubuntu:~$ mongodump -d so_test -c example -q '{"_id" : {"$gt" : {"$oid" : "4fad36290000000000000000"}}}' 
connected to: 127.0.0.1 
DATABASE: so_test to  dump/so_test 
    so_test.example to dump/so_test/example.bson 
     4 objects 

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 records