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# Function Score Query
> More info about function score query is in the [official elasticsearch docs][1]
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
```JSON
{
"query": {
"function_score": {
"query": {
"range": {
"price": {
"gte": 10,
"lte": 100
}
}
},
"functions": [
{
"linear": {
"price": {
"origin": 10,
"scale": 50,
"offset": 0,
"decay" : 0.5
}
}
}
]
}
}
}
```
In DSL
```php
$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
```JSON
{
"query": {
"function_score": {
"query": {
"match_all": {}
},
"functions": [
{
"weight": 2,
"filter": {
"range": {
"price": {
"gte": 10,
"lte": 40
}
}
}
}
]
}
}
}
```
In DSL:
```php
$functionScoreQuery = new FunctionScoreQuery(new MatchAllQuery());
$rangeFilter = new RangeFilter('price', ['gte' => 10, 'lte' => 100]);
$functionScoreQuery->addWeightFunction(2, $rangeFilter);
$search = new Search();
$search->addQuery($functionScoreQuery);
$queryArray = $search->toArray();
```
## Example Field Value Factor Function
```php
$functionScoreQuery = new FunctionScoreQuery(new MatchAllQuery());
$existsFilter = new ExistsFilter('price');
$functionScoreQuery->addFieldValueFactorFunction('price', 0.5, 'ln', $existsFilter);
$search = new Search();
$search->addQuery($functionScoreQuery);
$queryArray = $search->toArray();
```
Will result in
```JSON
{
"query": {
"function_score": {
"query": {
"match_all": {}
},
"functions": [
{
"field_value_factor": {
"field": "price",
"factor": 0.5,
"modifier": "ln"
},
"filter": {
"exists": {
"field": "price"
}
}
}
]
}
}
}
```
## Random function example
```php
$functionScoreQuery = new FunctionScoreQuery(new MatchAllQuery());
$functionScoreQuery->addRandomFunction();
$search = new Search();
$search->addQuery($functionScoreQuery);
$queryArray = $search->toArray();
```
Will result in
```JSON
{
"query": {
"function_score": {
"query": {
"match_all": {}
},
"functions": [
{
"random_score": {}
}
]
}
}
}
```
[1]: https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-function-score-query.html