Cannot do min aggregation on nested fields

[Burgov]

Elasticsearch version (bin/elasticsearch --version):
Tried on both 5.2.0 and 5.5.0

Plugins installed: [xpack]

JVM version (java -version):
1.8.0_91

OS version (uname -a if on a Unix-like system):
Linux x 4.4.0-81-generic #104-Ubuntu SMP Wed Jun 14 08:17:06 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

Description of the problem including expected versus actual behavior:
When doing a min/max aggregation on a nested field, rather than getting the expected value, you get null

Steps to reproduce:

PUT /test_index
{
   "settings": {
      "number_of_shards": 1
   },
   "mappings": {
      "doc": {
         "properties": {
            "entries": {
               "type": "nested",
               "properties": {
                  "name": {
                     "type": "keyword"
                  },
                  "position": {
                     "type": "long"
                  }
               }
            },
            "id": {
               "type": "keyword"
            },
            "version": {
               "type": "long"
            }
         }
      }
   }
}

PUT /test_index/doc/_bulk
{"index":{"_id":1}}
{"id":"i1","version":1,"entries":[{"name":"n1","position":1},{"name":"n2","position":2}]}
{"index":{"_id":2}}
{"id":"i1","version":2,"entries":[{"name":"n2","position":3},{"name":"n3","position":4}]}
{"index":{"_id":3}}
{"id":"i2","version":1,"entries":[{"name":"n1","position":8},{"name":"n2","position":7}]}
{"index":{"_id":4}}
{"id":"i2","version":2,"entries":[{"name":"n2","position":6},{"name":"n3","position":5}]}

POST /test_index/_search
{
   "aggs": {
      "id_terms": {
         "terms": {
            "field": "id"
         },
         "aggs": {
            "nested_entries": {
               "nested": {
                  "path": "entries"
               },
               "aggs": {
                  "filter_name": {
                     "filter": {
                        "term": {
                           "entries.name": "n2"
                        }
                     },
                     "aggs": {
                        "min_position": {
                           "min": {
                              "field": "position"
                           }
                        }
                     }
                  }
               }
            }
         }
      }
   }
}

expected output:

{
    // snip
   "aggregations": {
      "id_terms": {
         "doc_count_error_upper_bound": 0,
         "sum_other_doc_count": 0,
         "buckets": [
            {
               "key": "i1",
               "doc_count": 2,
               "nested_entries": {
                  "doc_count": 4,
                  "filter_name": {
                     "doc_count": 2,
                     "min_position": {
                        "value": 2,
                        "value_as_string": "2.0"
                     }
                  }
               }
            },
            {
               "key": "i2",
               "doc_count": 2,
               "nested_entries": {
                  "doc_count": 4,
                  "filter_name": {
                     "doc_count": 2,
                     "min_position": {
                        "value": 6,
                        "value_as_string": "6.0"
                     }
                  }
               }
            }
         ]
      }
   }
}

actual output:

{
    // snip
   "aggregations": {
      "id_terms": {
         "doc_count_error_upper_bound": 0,
         "sum_other_doc_count": 0,
         "buckets": [
            {
               "key": "i1",
               "doc_count": 2,
               "nested_entries": {
                  "doc_count": 4,
                  "filter_name": {
                     "doc_count": 2,
                     "min_position": {
                        "value": null
                     }
                  }
               }
            },
            {
               "key": "i2",
               "doc_count": 2,
               "nested_entries": {
                  "doc_count": 4,
                  "filter_name": {
                     "doc_count": 2,
                     "min_position": {
                        "value": null
                     }
                  }
               }
            }
         ]
      }
   }
}

[costin]

You need to specify the full path of the nested field just its name in a similar fashion to filter in filter_name: "field": "position" -> "field": "entries.position"

Hth

[Burgov]

@costin ha, you're right, i missed it in my example, and when I add it, it works. However, I have a case where it doesn't work even though I do add that path part. Thought I had produced a minimum case for reproducing it, but apparently I didn't... back to the drawing table.