ELASTICSEARCH - Get a count of values from the most recent document - elasticsearch

Question

I can't get a count of fields with a filtered document value.
I have this json
``
{
"took" : 6,
"timed_out" : false,
"_shards" : {
"total" : 1,
"successful" : 1,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : {
"value" : 2,
"relation" : "eq"
},
"max_score" : 1.0,
"hits" : [
{
"_index" : "net",
"_type" : "_doc",
"_id" : "RTHRTH",
"_score" : 1.0,
"_source" : {
"created_at" : "2020-05-31 19:01:01",
"data" : [...]
{
"_index" : "net",
"_type" : "_doc",
"_id" : "LLLoIJBHHM",
"_score" : 1.0,
"_source" : {
"created_at" : "2020-06-23 15:11:59",
"data" : [...]
}
}
]
}
}
``
In the "data" field, there are more fields within other fields respectively.
I want to filter the most recent document, and then count a certain value in the most recent document.
This is my query:
`{
"query": {
"match": {
"name.keyword": "net"
}
},
"sort": [
{
"created_at.keyword": {
"order": "desc"
}
}
],
"size": 1,
"aggs": {
"CountValue": {
"terms": {
"field": "data.add.serv.desc.keyword",
"include": "nginx"
}
}
}
}`
And the output is:
`{
"took" : 3,
"timed_out" : false,
"_shards" : {
"total" : 1,
"successful" : 1,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : {
"value" : 2,
"relation" : "eq"
},
"max_score" : null,
"hits" : [ ]
},
"aggregations" : {
"CountValue" : {
"doc_count_error_upper_bound" : 0,
"sum_other_doc_count" : 0,
"buckets" : [
{
"key" : "nginx",
"doc_count" : 2
}
]
}
}`
I suspect that doc_count is the number of documents the value appears in, not the number of times the value is repeated within the filtered document.
Any advice I will be very grateful!

Answer 1

Unless any of the fields under the path data.add.serv are of the nested type, the terms agg will produce per-whole-doc results, not per-field.
Exempli gratia:
POST example/_doc
{
"serv": [
{
"desc": "nginx"
},
{
"desc": "nginx"
},
{
"desc": "nginx"
}
]
}
then
GET example/_search
{
"size": 0,
"aggs": {
"NAME": {
"terms": {
"field": "serv.desc.keyword"
}
}
}
}
produces doc_count==1.
When, however, specified as nested:
DELETE example
PUT example
{
"mappings": {
"properties": {
"serv": {
"type": "nested"
}
}
}
}
POST example/_doc
{"serv":[{"desc":"nginx"},{"desc":"nginx"},{"desc":"nginx"}]}
then
GET example/_search
{
"size": 0,
"aggs": {
"NAME": {
"nested": {
"path": "serv"
},
"aggs": {
"NAME": {
"terms": {
"field": "serv.desc.keyword"
}
}
}
}
}
}
we end up with doc_count==3.
This has to do with the way non-nested array types are flattened and de-duplicated. At the end, you may need to reindex your collections after having applied the nested mapping.
EDIT
In order to only take the latest doc, you could do the following:
PUT example
{
"mappings": {
"properties": {
"serv": {
"type": "nested"
},
"created_at": {
"type": "date",
"format": "yyyy-MM-dd HH:mm:ss"
}
}
}
}
then
POST example/_doc
{
"created_at" : "2020-05-31 19:01:01",
"serv": [
{
"desc": "nginx"
},
{
"desc": "nginx"
},
{
"desc": "nginx"
}
]
}
POST example/_doc
{
"created_at" : "2020-06-23 15:11:59",
"serv": [
{
"desc": "nginx"
},
{
"desc": "nginx"
}
]
}
then use a terms agg of size 1, sorted by timestamp desc:
GET example/_search
{
"size": 0,
"aggs": {
"NAME": {
"terms": {
"field": "created_at",
"order": {
"_term": "desc"
},
"size": 1
},
"aggs": {
"NAME2": {
"nested": {
"path": "serv"
},
"aggs": {
"NAME": {
"terms": {
"field": "serv.desc.keyword"
}
}
}
}
}
}
}
}