Nested array of objects aggregation in Elasticsearch - elasticsearch

Question

Documents in the Elasticsearch are indexed as such
Document 1
{
"task_completed": 10
"tagged_object": [
{
"category": "cat",
"count": 10
},
{
"category": "cars",
"count": 20
}
]
}
Document 2
{
"task_completed": 50
"tagged_object": [
{
"category": "cars",
"count": 100
},
{
"category": "dog",
"count": 5
}
]
}
As you can see that the value of the category key is dynamic in nature. I want to perform a similar aggregation like in SQL with the group by category and return the sum of the count of each category.
In the above example, the aggregation should return
cat: 10,
cars: 120 and
dog: 5
Wanted to know how to write this aggregation query in Elasticsearch if it is possible. Thanks in advance.

Answer 1

You can achieve your required result, using nested, terms, and sum aggregation.
Adding a working example with index mapping, search query and search result
Index Mapping:
{
"mappings": {
"properties": {
"tagged_object": {
"type": "nested"
}
}
}
}
Search Query:
{
"size": 0,
"aggs": {
"resellers": {
"nested": {
"path": "tagged_object"
},
"aggs": {
"books": {
"terms": {
"field": "tagged_object.category.keyword"
},
"aggs":{
"sum_of_count":{
"sum":{
"field":"tagged_object.count"
}
}
}
}
}
}
}
}
Search Result:
"aggregations": {
"resellers": {
"doc_count": 4,
"books": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": "cars",
"doc_count": 2,
"sum_of_count": {
"value": 120.0
}
},
{
"key": "cat",
"doc_count": 1,
"sum_of_count": {
"value": 10.0
}
},
{
"key": "dog",
"doc_count": 1,
"sum_of_count": {
"value": 5.0
}
}
]
}
}
}