How to filter on nested document length by script in Elasticsearch - elasticsearch

Question

I am trying to filter documents that have at least a given amount of items in a nested field, but I keep getting the following exception:
"caused_by" : {
"type" : "illegal_argument_exception",
"reason" : "No field found for [items] in mapping"
}
Here's an example code to reproduce:
PUT store
{
"mappings": {
"properties": {
"subject": {
"type": "keyword"
},
"items": {
"type": "nested",
"properties": {
"name": {
"type": "keyword"
},
"count": {
"type": "integer"
}
}
}
}
}
}
POST store/_bulk?refresh=true
{"create":{"_index":"store","_id":"1"}}
{"type":"appliance","items":[{"name":"Color TV"}]}
{"create":{"_index":"store","_id":"2"}}
{"type":"vehicle","items":[{"name":"Car"},{"name":"Bicycle"}]}
{"create":{"_index":"store","_id":"3"}}
{"type":"instrument","items":[{"name":"Guitar"},{"name":"Piano"},{"name":"Drums"}]}
GET store/_search
{
"query": {
"bool": {
"filter": [
{
"script": {
"script": {
"source": "doc['items'].size() > 1"
}
}
}
]
}
}
}
Please note that this is only a simplified filter script of what I really wanted to do, and if I can get over this, I will probable be able to solve my task as well.
Any help would be appreciated.

Answer 1

I ended up solving it with a custom score approach:
GET store/_search
{
"min_score": 0.1,
"query": {
"function_score": {
"query": {
"match_all": {}
},
"functions": [
{
"script_score": {
"script": {
"source": "params['_source']['items'].length > 1 ? 1 : 0"
}
}
}
]
}
}
}