Sorting by a nested field in elasticsearch

Question

If I had a data structure that looked like this

[{"_id" 1 
 "scores" [{"student_id": 1, "score": 100"}, {"student_id": 2, "score": 80"}
 ]}, 
{"_id" 2
 "scores" [{"student_id": 1, "score": 20"}, {"student_id": 2, "score": 90"}
 ]}]

Would it be possible to sort this dataset by student_1's score or by student_2's score?

For example if I sorted descending by student 1's score, I would get document 1,2, but if I sorted descending by student 2's score, I would get 2,1.

I could re-arrange the data, but I don't want to use another index because there's a bunch of metadata not included above for brevity. Thanks!

Could you please provide index mapping ?

Sagar Patel
– Sagar Patel

2022-12-02 04:26:51 +00:00
Commented Dec 2, 2022 at 4:26 — Sagar Patel
– Sagar Patel, Commented Dec 2, 2022 at 4:26

llermaly · Accepted Answer · 2022-12-02 07:33:57Z

1

Yes, it is possible. You must use "nested" field type for your scores, that way you can keep the relation between each student_id and its score.

You can read an article I wrote about that subject: https://opster.com/guides/elasticsearch/data-architecture/elasticsearch-nested-field-object-field/

Now the example:

Mappings

PUT test_students
{
  "mappings": {
    "properties": {
      "scores": {
        "type": "nested",
        "properties": {
          "student_id": {
            "type": "keyword"
          },
          "score": {
            "type": "long"
          }
        }
      }
    }
  }
}

Documents

PUT test_students/_doc/1
{
  "scores": [{"student_id": 1, "score": 100}, {"student_id": 2, "score": 80}]
}

PUT test_students/_doc/2
{
  "scores": [{"student_id": 1, "score": 20}, {"student_id": 2, "score": 90}]
}

Query


POST test_students/_search
{
   "sort" : [
       {
          "scores.score" : {
             "mode" :  "max",
             "order" : "desc",
             "nested": {
                "path": "scores",
                "filter": {
                   "term" : { "scores.student_id" : "2" }
                }
             }
          }
       }
    ]
}

answered Dec 2, 2022 at 7:33

llermaly

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1 Comment

jdkealy Over a year ago

thank you! works perfecrtly

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