adding a script-based field to an elasticSearch index mapping - elasticsearch

Question

I am following the following docs: https://www.elastic.co/guide/en/elasticsearch/reference/current/runtime-indexed.html
I have a field which I would like to not be scripted on runtime but rather on index-time, and according to above I can do that simply by putting the field and its script inside the mapping object as normal.
Here is a simplified version of the index I'm trying to create
{
"settings": {
"analysis": {
"analyzer": {
"case_insensitive_analyzer": {
"type": "custom",
"filter": ["lowercase"],
"tokenizer": "keyword"
}
}
}
},
"mappings": {
"properties": {
"id": {
"type": "text"
},
"events": {
"properties": {
"fields": {
"type": "text"
},
"id": {
"type": "text"
},
"event": {
"type": "text"
},
"time": {
"type": "date"
},
"user": {
"type": "text"
},
"state": {
"type": "integer"
}
}
},
"eventLast": {
"type": "date",
"on_script_error": "fail",
"script": {
"source": "def events = doc['events']; emit(events[events.length-1].time.value"
}
}
}
}
}
I'm getting this 400 error back:
{
"error": {
"root_cause": [
{
"type": "mapper_parsing_exception",
"reason": "unknown parameter [script] on mapper [eventLast] of type [date]"
}
],
"type": "mapper_parsing_exception",
"reason": "Failed to parse mapping [_doc]: unknown parameter [script] on mapper [eventLast] of type [date]",
"caused_by": {
"type": "mapper_parsing_exception",
"reason": "unknown parameter [script] on mapper [eventLast] of type [date]"
}
},
"status": 400
}
Essentially I'm trying to create a scripted indexed field that is calculated off the last event time in the events array of the document.
Thanks

Answer 1

Tldr;
As the error states, you can not define your script in here.
There is a specific way to create runtime fields in elasticsearch.
You need to put the definition at the root of the json in the runtime object.
Solution
{
"settings": {
"analysis": {
"analyzer": {
"case_insensitive_analyzer": {
"type": "custom",
"filter": ["lowercase"],
"tokenizer": "keyword"
}
}
}
},
"runtime": {
"eventLast": {
"type": "date",
"on_script_error": "fail",
"script": {
"source": "def events = doc['events']; emit(events[events.length-1].time.value"
}
}
},
"mappings": {
"properties": {
"id": {
"type": "text"
},
"events": {
"properties": {
"fields": {
"type": "text"
},
"id": {
"type": "text"
},
"event": {
"type": "text"
},
"time": {
"type": "date"
},
"user": {
"type": "text"
},
"state": {
"type": "integer"
}
}
}
}
}
}