How to filter by field values in ElasticSearch?

Question

Given the ElasticSearch document below:

{
    "_id": "3330481",
    "_type": "user",
    "_source": {
        "id": "3330481",
        "following": ["1", "2", "3", ... , "15000"]
    }
}

For a given user list ["50", "51", "52"] I want to check which ones are followed by the user with id 3330481. Since she is following 15000 users, I don't want to get the whole list and then check it locally.

Is there any way to retrieve only the relevant users?

Answer 1

I am not sure whether you can fetch a sub-array from a doc.

However, one way of achieving this is by using nested fields. You can change the schema of following field to be nested as below.

 {
        "id": "3330481",
        "following": [
              {"userId":"1"}, {"userId":"2"},{"userId": "3"}, ... ]
 }

Then you can use inner_hits to retrieve your matching elements in the array as below.

{
    "query" : {
        "nested" : {
            "path" : "following",
            "query" : {
                "terms" : {"following.userId" : ["50","51","53"]}
            },
            "inner_hits" : {
                "size":0 // fetches all 
            }
        }
    }
}