Elastic script_score, only count specific array elements

Question

I have a bunch of objects like this one in Elastic:

{
          "id" : "b397ab9c-2bab-4cce-a419-ba6b23545772",
          "name": "Alice",
          // other fields omitted
          "foo" : [
            {
              "id" : "1",
              "bar" : 20
            },
            {
              "id" : "2",
              "bar" : 20
            }
           ]
},
{
          "id" : "826784cb-7dcd-4d2c-b444-a466032a7b06",
          "name": "Bob",
          // other fields omitted
          "foo" : [
            {
              "id" : "1",
              "bar" : 15
            }
           ]
}

I am trying to make a score based on any elements in foo of which the id is 2. So in the above objects, Alice has a score of 20 and Bob has a score of 0 (as there's no element with id 2 in his foo array. I'm however a bit stuck in how to have my script_score look for the specific element. Here is my query:

  "query": {
    "function_score": {
      "score_mode": "max", 
      "functions": [
        {
          "filter": {
            "term": {
              "foo.id": {
                "value": "2"
              }
            }
          },
          "script_score": {
            "script": {
              "source": "doc['foo'].values /* what goes here? */",
              "params": {
              }
            }
          }
        }
      ]
    }
  }

No, the foo key is in the root of the object. It is an array that contains simple objects. — yesman, Nov 30 '20 at 14:55

score 1 · Accepted Answer · answered Nov 30 '20 at 16:56

When foo is not of type nested, you'll have lost the connection between id and bar due to value flattenning.

After you've reconfigured your mapping to be nested, you can do

{
  "query": {
    "nested": {
      "path": "foo",
      "query": {
        "function_score": {
          "score_mode": "max",
          "functions": [
            {
              "script_score": {
                "script": {
                  "source": "if (doc['foo.id.keyword'].value == '2') { def bar = doc['foo.bar'].value; return bar } return 0",
                  "params": {}
                }
              }
            }
          ]
        }
      }
    }
  }
}

but without the filter because that'd have filtered out doc#2 since it does not meet that condition and you probably want to do some sort of a scripted fallback.

Do note that once you're in the nested context, you don't have access to other object groups in your foo array. In other words, when you're in id: 2, you don't see the id: 1 group. More info here.

Thanks Joe, I'll try reconfiguring my mapping tomorrow. – yesman Nov 30 '20 at 20:57 — yesman, Nov 30 '20 at 20:57
Got it working, thanks. I'll buy you a coffee tonight! – yesman Dec 02 '20 at 09:48 — yesman, Dec 02 '20 at 09:48

Elastic script_score, only count specific array elements

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