Reverse_nested aggregation + top hits : get parent and nested data at the same time - elasticsearch

Question

Do you know how to use reverse_nested aggregation to get both the parent and ONLY the nested data inside my top hit aggregations ?
The 'ONLY' part is the problem right now.
This is my mapping :
{
"ticket": {
"mappings": {
"properties": {
"name": {
"type": "keyword"
}
},
"tasks": {
"type": "nested",
"properties": {
"string_task_name": {
"type": "keyword"
}
}
}
}
}
}
My query uses top hits and reverse nested aggs.
{
"aggs": {
"object_tasks": {
"nested": {
"path": "object_tasks"
},
"aggs": {
"filter_by_tasks_attribute": {
"filter": {
"bool": {
"must": [
{
"wildcard": {
"object_tasks.string_task_name.keyword": "*"
}
}
]
}
},
"aggs": {
"using_reverse_nested": {
"reverse_nested": {
"path": "object_tasks"
},
"aggs": {
"names": {
"top_hits": {
"_source": {
"includes": [
"object_tasks.string_task_name",
"string_name"
]
},
"sort": [
{
"object_tasks.string_task_name.keyword": {
"order": "desc"
}
}
],
"from": 0,
"size": 10
}
}
}
}
}
}
}
}
}
}
{
"hits": {
"total": {
"value": 25,
"relation": "eq"
},
"max_score": null,
"hits": [
{
"_index": "random_index",
"_type": "_doc",
"_id": "5",
"_score": null,
"_source": {
"object_tasks": [ ================> I don't want all these tasks names, I just want the task name of the current nested object I am in.
{
"string_task_name": "task1"
},
{
"string_task_name": "task2"
},
{
"string_task_name": "task3"
},
{
"string_task_name": "task4"
}
],
"string_name": "Dummy Ticket 854"
},
"sort": [
"seek_a_sme"
]
}
]
}
}
As you can see the result is giving me 4 tasks name. What I want is to return only 1 task name.
The only workaround I have found is to copy the data of tickets inside the tasks. But if I can avoid it that would be awesome.

Answer 1

I don't want all these tasks names, I just want the task name of the current nested object I am in.
The statement "of the current nested object I'm in" implies that you are inside of a nested context but you cannot be in one when you escape it through reverse_nested…
I'm not sure if I truly understood what you're gunning for here but you could aggregate on the terms of object_tasks.string_task_name.keyword and the keys of this aggregation would then function as the individual "current nested objects" that you're after:
{
"size": 0,
"aggs": {
"object_tasks": {
"nested": {
"path": "object_tasks"
},
"aggs": {
"filter_by_tasks_attribute": {
"filter": {
"bool": {
"must": [
{
"wildcard": {
"object_tasks.string_task_name.keyword": "*"
}
}
]
}
},
"aggs": {
"by_string_task_name": {
"terms": {
"field": "object_tasks.string_task_name.keyword",
"order": {
"_key": "desc"
},
"size": 10
},
"aggs": {
"using_reverse_nested": {
"reverse_nested": {},
"aggs": {
"names": {
"top_hits": {
"_source": {
"includes": [
"string_name"
]
},
"from": 0,
"size": 10
}
}
}
}
}
}
}
}
}
}
}
}
yielding
"aggregations" : {
"object_tasks" : {
...
"filter_by_tasks_attribute" : {
...
"by_string_task_name" : {
...
"buckets" : [
{
"key" : "task4", <--
...
"using_reverse_nested" : {
...
"names" : {
"hits" : {
...
"hits" : [
{
...
"_source" : {
"string_name" : "Dummy Ticket 854" <--
}
}
]
}
}
}
},
{
"key" : "task3", <--
...
},
{
"key" : "task2", <--
...
},
{
"key" : "task1", <--
...
}
}
]
}
}
}
}
Notice that the top_hits aggregation doesn't need to be sorted anymore -- object_tasks.string_task_name.keyword will always be the same for any currently aggregated terms bucket. What I did instead was order this terms aggregation by _key which works the same way as a top_hits sort would have. BTW -- yours was missing the nested path parameter.