Hi @MWD_Wajih_N_A,
Atlas Triggers use the MongoDB Change Streams API which is a standard feature of modern MongoDB Server versions (3.6+). Change Streams use the replication oplog in their underlying implementation, but provide a stable API to subscribe and react to changes for a single collection, database, or an entire deployment (replica set or sharded cluster). You should use the Change Streams API rather than directly reading the oplog.
Atlas triggers are provided via Atlas’ cluster management interface. You can implement similar logic in an on-premise deployment by creating a persistent application using change streams.
The On-Demand Materialised Views documentation includes examples of creating and updating data using the $merge aggregation functionality in MongoDB 4.2+. The documentation examples use the mongo shell for illustration purposes, but you can translate those approaches into any of the supported drivers for MongoDB 4.2+.
You can find examples of working with change streams in different drivers in the MongoDB manual. For example: Open a Change Stream.
Regards,
Stennie