How to get sum of diferent fields / array values in elasticsearch? - elasticsearch

Question

Using Elasticsearch 7.9.0
My document looks like this
{
"student": {
"marks": [
{
"sub": 80
},
{
"sub": 90
},
{
"sub": 100
}
]
}
}
I need one more field total_marks in the response of GET API
Something like this
{
"hits": [
{
"_index": "abc",
"_type": "_doc",
"_id": "blabla",
"_score": null,
"_source": {
"student": {
"marks": [
{
"sub": 80
},
{
"sub": 90
},
{
"sub": 100
}
]
}
},
"total_marks": 270
}
]
}
I tried using script_fields
My query is
GET sample/_search
{
"query": {
"match_all": {}
},
"script_fields": {
"total_marks": {
"script": {
"source": """double sum = 0.0;
for( item in params._source.student.marks)
{ sum = sum + item.sub }
return sum;"""
}
}
}
}
I got response as
{
"hits": [
{
"_index": "abc",
"_type": "_doc",
"_id": "blabla",
"_score": null,
"_source": {
"student": {
"marks": [
{
"sub": 80
},
{
"sub": 90
},
{
"sub": 100
}
]
}
},
"fields": {
"total_marks": [
270
]
}
}
]
}
Is thare any way to get as expected?
Any better/optimal solution would be helps a lot.
Thank you.

Answer 1

Terms aggregation and sum aggregation can be used to find total marks per group
{
"aggs": {
"students": {
"terms": {
"field": "student.id.keyword",
"size": 10
},
"aggs": {
"total_marks": {
"sum": {
"field": "student.marks.sub"
}
}
}
}
}
}
Result
"aggregations" : {
"students" : {
"doc_count_error_upper_bound" : 0,
"sum_other_doc_count" : 0,
"buckets" : [
{
"key" : "1",
"doc_count" : 1,
"total_marks" : {
"value" : 270.0
}
}
]
}
}
This will be faster than script but Pagination will be easier in query as compared to aggregation. So choose accordingly.
Best option may be to have it calculated at index time. If those fields are not changing frequently.