Elasticsearch Nest : Fetching random documents

Question

I am trying to get random records using Elastic Search NEST client. Is there any way to do this?

Answer 1

To compliment @pickypg's answer, here's an example of how to compose a function_score query with a random_score function in NEST:

client.Search<MyType>(s => s
    .Query(q => q
        .FunctionScore(fs => fs
            .Query(fq => fq.MatchAll())
            .RandomScore()
        )
    )
);

Answer 2

ES 7.x

NEST Way :

var result = _elastic.Search<dynamic>(s => s
        .Query(q => q
        .FunctionScore(fs => fs.Functions(f => f.RandomScore())
        .Query(fq => fq.MatchAll()))));

raw query way :

 GET index-name/_search
    "size": 1,
    "query": {
        "function_score": {
                "query" : { "match_all": {} },
               "random_score": {}
        }
    }
}

Answer 3

This is more of an Elasticsearch question than one related to NEST. With that in mind, you can do this using a random_score function in Elasticsearch. random_score is one of the many function_score s available in Elasticsearch -- including scripted scores -- and it can be used to control the _score for each matching document.

Relative to Elasticsearch's REST API

curl -XGET localhost:9200/your-index/your-type/_search -d '{
  "query" : {
    "function_score": {
      "query": { "match_all": {} },
      "random_score" : { }
    }
  },
  "size" : 1
}'

You can control the seed used by the random number generator or you can create your own random function score. The current random_score implementation loads the _uid field from the index (the unique identifier), which the documentation notes can be memory intensive.