Using Transform for document count when document updated

Elastic Stack Elasticsearch
2

Is the above understanding is correct - transform will not delete {status : "new",count : "1"} from transform dest index in above senario?

This is correct.

like add an field indicating when the transform result is generated/updated

This other answer may help - Creating an ingest pipeline for transforms.

  • create an ingest pipeline that adds a timestamp field
  • use the Put Transform API to set the pipeline in the dest.pipeline field

Any document added or updated in the destination index will get a new timestamp.

It would look something like:

PUT _ingest/pipeline/pipeline_add_ingest_timestamp
{ 
  "description": "Adds event.ingested field which represents time of ingestion.",
  "processors": [
    {
      "set": {
        "field": "event.ingested",
        "value": "{{_ingest.timestamp}}"
      }
    }
  ]
}

PUT _transform/new_orders_count
{
  ...
  "dest": {
    "index": "dest_index_name",
    "pipeline": "pipeline_add_ingest_timestamp"
  },
  ...
}