Find min value of field in nested array object after aggregation - elasticsearch

Question

I would like to find the minimum value of a field in a nested array object after aggregation.
Data example:
[
{
"id": "i1",
"version": 1,
"entries": [
{
"name": "n1",
"position": 1
}, {
"name": "n2",
"position": 2
}
]
}, {
"id": "i1"
"version": 2,
"entries": [
{
"name": "n2",
"position": 3
}, {
"name": "n3",
"position": 4
}
]
},
{
"id": "i2",
"version": 1,
"entries": [
{
"name": "n1",
"position": 8
}, {
"name": "n2",
"position": 7
}
]
}, {
"id": "i2"
"version": 2,
"entries": [
{
"name": "n2",
"position": 6
}, {
"name": "n3",
"position": 5
}
]
}
]
Pseudo Query:
SELECT min(entries["n2"].position) WHERE entries.name="n2" GROUP BY id;
Expected Result:
[
{
"id": "i1",
"min(position)": 2
}, {
"id": "i2",
"min(position)": 6
}
]
I can do this in code, but it's not performant, as I need to return the document sources which can be quite large.
I am thinking of denormalizing the data, but would like to first know if this request is not possible at all.

Answer 1

You can do it by nesting several aggregations like this:
terms agg -> nested agg -> filter agg -> min agg
To test it I set up an index:
PUT /test_index
{
"settings": {
"number_of_shards": 1
},
"mappings": {
"doc": {
"properties": {
"entries": {
"type": "nested",
"properties": {
"name": {
"type": "string"
},
"position": {
"type": "long"
}
}
},
"id": {
"type": "string"
},
"version": {
"type": "long"
}
}
}
}
}
And indexed your docs:
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}]}
Here is the query:
POST /test_index/_search?search_type=count
{
"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"
}
}
}
}
}
}
}
}
}
}
and the result:
{
"took": 2,
"timed_out": false,
"_shards": {
"total": 1,
"successful": 1,
"failed": 0
},
"hits": {
"total": 4,
"max_score": 0,
"hits": []
},
"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"
}
}
}
}
]
}
}
}
Here is the code I used all together:
http://sense.qbox.io/gist/34a013099ef07fb527d9d7cf8490ad1bbafa718b