ES query to group by parent_id - elasticsearch

Question

I have the below data in my elasticsearch. I would like to query these data with group.
{
"id" : "001",
"parent_id" : "001",
"name" : "test001"
},
{
"id" : "002",
"parent_id" : "001",
"name" : "test002"
},
{
"id" : "003",
"parent_id" : "001",
"name" : "test003"
}
{
"id" : "004",
"parent_id" : "004",
"name" : "test004"
}
Here is my expected format:
{
"id" : "001",
"parent_id" : "001",
"name" : "test001"
"children": [
{
"id" : "002",
"parent_id" : "001",
"name" : "test002"
},
{
"id" : "003",
"parent_id" : "001",
"name" : "test003"
}
]
},
{
"id" : "004",
"parent_id" : "004",
"name" : "test004"
}
Is there any way I can achieve this using elastic search query?

Answer 1

Assuming that parent_id is of the keyword field type, and/or has a multi-field mapping similar to:
"parent_id" : {
"type" : "text",
"fields" : {
"keyword" : { <---
"type" : "keyword"
}
}
}
you could first group all your documents by parent_id.keyword and then list all the children (including #001) using a top_hits aggregation:
POST my-index/_search?filter_path=aggregations.*.buckets.key,aggregations.*.buckets.children.hits.hits._source
{
"size": 0,
"aggs": {
"by_parent_id": {
"terms": {
"field": "parent_id.keyword",
"size": 10
},
"aggs": {
"children": {
"top_hits": {
"sort": [
{
"id.keyword": {
"order": "asc"
}
}
],
"size": 10
}
}
}
}
}
}
yielding
{
"aggregations" : {
"by_parent_id" : {
"buckets" : [
{
"key" : "001",
"children" : {
"hits" : {
"hits" : [
{
"_source" : {
"id" : "001",
"parent_id" : "001",
"name" : "test001"
}
},
{
"_source" : {
"id" : "002",
"parent_id" : "001",
"name" : "test002"
}
},
{
"_source" : {
"id" : "003",
"parent_id" : "001",
"name" : "test003"
}
}
]
}
}
},
{
"key" : "004",
"children" : {
"hits" : {
"hits" : [
{
"_source" : {
"id" : "004",
"parent_id" : "004",
"name" : "test004"
}
}
]
}
}
}
]
}
}
}
You can also sort the children by a metric of your choice — perhaps by id.keyword:
POST my-index/_search?filter_path=aggregations.*.buckets.key,aggregations.*.buckets.children.hits.hits._source
{
"size": 0,
"aggs": {
"by_parent_id": {
"terms": {
"field": "parent_id.keyword",
"size": 10
},
"aggs": {
"children": {
"top_hits": {
"sort": [ <---
{
"id.keyword": {
"order": "asc"
}
}
],
"size": 10
}
}
}
}
}
}
Finally, you can control the order of the top-level, terms aggregation too.