Fields in the _source field can be accessed directly in a pipeline definition simply by either using the field name or adding the _source prefix to the field name.
On the other hand, if you are referring to the value of a field, then you can use the {{field_name}} template snippet to retrieve the value. Let's take an example of using a set processor to add an ingest_timestamp field to the document, which records the timestamp value when the ingest processing occurs. This value is provided by the API, as we mentioned in the result of the _simulate pipeline example. The partially relevant codes are as follows:
"processors": [{
"set": {
"field": "ingest_timestamp",
"value": "{{_ingest.timestamp}}"
}
}
Dynamic mapping fields and field values are also supported in the same...
