Mongodb get new values from collection without timestamp-CodePudding

I want to fetch added new values from mongodb collections without timestamp value. I guess only choice using objectid field. I using test dataset on github. "https://raw.githubusercontent.com/mongodb/docs-assets/primer-dataset/primer-dataset.json" For example if I add new data to this collection, how ı fetch or how ı find these new values. Some mongodb collections using timestamp value, and I use this timestamp value for get new values. But ı do not know, how ı find without timestamp. Example dataset ; enter image description here

I want like this filter. but it doesn't work

{_id: {$gt: '622e04d69edb39455e06d4af'}}

CodePudding user response：

If you don't want to create a new field in the document.

SomeGlobalObj = ObjectId[] // length limit is 10
 // you will need Redis or other outside storage if you have multi server

SomeGlobalObj.shift(newDocumentId)
SomeGlobalObj = SomeGlobalObj.slice(0,10)
//Make sure to keep the latest 10 IDs.

Now, if you want to retrieve the latest document, you can use this array.

If the up-to-date thing you're talking about is, disappears after checking, you can remove it from this array after query.

CodePudding user response：

In the comments you mentioned that you want to do this using Python, so I shall answer from that perspective.

In Mongo, an ObjectId is composed of 3 sections:

a 4-byte timestamp value, representing the ObjectId's creation, measured in seconds since the Unix epoch

a 5-byte random value generated once per process. This random value is unique to the machine and process.

a 3-byte incrementing counter, initialized to a random value

Because of this, we can use the ObjectId to sort or filter by created timestamp. To construct an ObjectId for a specific date, we can use the following code:

gen_time = datetime.datetime(2010, 1, 1)
dummy_id = ObjectId.from_datetime(gen_time)
result = collection.find({"_id": {"$lt": dummy_id}})

Source: objectid - Tools for working with MongoDB ObjectIds

This example will find all documents created before 2010/01/01. Substituting $gt would allow this query to function as you desire.

If you need to get the timetamp from an ObjectId, you can use the following code:

id = myObjectId.generation_time