Function Score Query

More info about function score query is in the official elasticsearch docs

The function score query allows you to modify the score of documents that are retrieved by a query. This can be useful if, for example, a score function is computationally expensive and it is sufficient to compute the score on a filtered set of documents.

Example with linear decay function

{
  "query": {
    "function_score": {
      "query": {
        "range": {
          "price": {
            "gte": 10,
            "lte": 100
          }
        }
      },
      "functions": [
        {
          "linear": {
            "price": {
              "origin": 10,
              "scale": 50,
              "offset": 0,
              "decay" : 0.5
            }
          }
        }
      ]
    }
  }
}

In DSL

$rangeQuery = new RangeQuery('price');
$rangeQuery->addParameter(RangeQuery::GTE, 10);
$rangeQuery->addParameter(RangeQuery::LTE, 100);
$functionScoreQuery = new FunctionScoreQuery($rangeQuery);
$functionScoreQuery->addDecayFunction(
    'linear',
    'price',
    [
        'origin' => 10,
        'scale' => 50,
        'offset' => 0,
        'decay' => 0.5
    ]
);

$search = new Search();
$search->addQuery($functionScoreQuery);

$queryArray = $search->toArray();

Example weight function to multiply score of subset

{
  "query": {
    "function_score": {
      "query": {
        "match_all": {}
      },
      "functions": [
        {
          "weight": 2,
          "filter": {
            "range": {
              "price": {
                "gte": 10,
                "lte": 40
              }
            }
          }
        }
      ]
    }
  }
}

In DSL:

$functionScoreQuery = new FunctionScoreQuery(new MatchAllQuery());
$rangeFilter = new RangeQuery('price', ['gte' => 10, 'lte' => 100]);
$functionScoreQuery->addWeightFunction(2, $rangeFilter);

$search = new Search();
$search->addQuery($functionScoreQuery);

$queryArray = $search->toArray();

Example Field Value Factor Function

$functionScoreQuery = new FunctionScoreQuery(new MatchAllQuery());
$existsQuery = new ExistsQuery('price');
$functionScoreQuery->addFieldValueFactorFunction('price', 0.5, 'ln', $existsQuery, 0);

$search = new Search();
$search->addQuery($functionScoreQuery);

$queryArray = $search->toArray();

Will result in

{
  "query": {
    "function_score": {
      "query": {
        "match_all": {}
      },
      "functions": [
        {
          "field_value_factor": {
            "field": "price",
            "factor": 0.5,
            "modifier": "ln"
          },
          "filter": {
            "exists": {
              "field": "price"
            }
          }
        }
      ]
    }
  }
}

Random function example

$functionScoreQuery = new FunctionScoreQuery(new MatchAllQuery());
$functionScoreQuery->addRandomFunction();

$search = new Search();
$search->addQuery($functionScoreQuery);

$queryArray = $search->toArray();

Will result in

{
  "query": {
    "function_score": {
      "query": {
        "match_all": {}
      },
      "functions": [
        {
          "random_score": {}
        }
      ]
    }
  }
}