org.apache.lucene.expressions

Class Expression

java.lang.Object

org.apache.lucene.expressions.Expression

public abstract class Expression
extends Object

Base class that computes the value of an expression for a document.

Example that sorts based on an expression:

   // compile an expression:
   Expression expr = JavascriptCompiler.compile("sqrt(_score) + ln(popularity)");
   
   // SimpleBindings just maps variables to SortField instances
   SimpleBindings bindings = new SimpleBindings();
   bindings.add(new SortField("_score", SortField.Type.SCORE));
   bindings.add(new SortField("popularity", SortField.Type.INT));
   
   // create a sort field and sort by it (reverse order)
   Sort sort = new Sort(expr.getSortField(bindings, true));
   Query query = new TermQuery(new Term("body", "contents"));
   searcher.search(query, 10, sort);
 

Example that modifies the scores produced by the query:

   // compile an expression:
   Expression expr = JavascriptCompiler.compile("sqrt(_score) + ln(popularity)");

   // SimpleBindings just maps variables to SortField instances
   SimpleBindings bindings = new SimpleBindings();
   bindings.add(new SortField("_score", SortField.Type.SCORE));
   bindings.add(new SortField("popularity", SortField.Type.INT));

   // create a query that matches based on body:contents but
   // scores using expr
   Query query = new FunctionScoreQuery(
       new TermQuery(new Term("body", "contents")),
       expr.getDoubleValuesSource(bindings));
   searcher.search(query, 10);
 

See Also:

JavascriptCompiler.compile(java.lang.String)

WARNING: This API is experimental and might change in incompatible ways in the next release.

Field Summary

Fields

Modifier and Type	Field and Description
String	sourceText The original source text
String[]	variables Named variables referred to by this expression

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	Expression(String sourceText, String[] variables) Creates a new Expression.

Method Summary

Modifier and Type	Method and Description
abstract double	evaluate(DoubleValues[] functionValues) Evaluates the expression for the current document.
DoubleValuesSource	getDoubleValuesSource(Bindings bindings) Get a DoubleValuesSource which can compute the value of this expression in the context of the given bindings.
Rescorer	getRescorer(Bindings bindings) Get a Rescorer, to rescore first-pass hits using this expression.
SortField	getSortField(Bindings bindings, boolean reverse) Get a sort field which can be used to rank documents by this expression.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

sourceText

public final String sourceText

The original source text

variables

public final String[] variables

Named variables referred to by this expression

Constructor Detail

Expression

protected Expression(String sourceText,
                     String[] variables)

Creates a new Expression.

Parameters:

sourceText - Source text for the expression: e.g. ln(popularity)

variables - Names of external variables referred to by the expression

Method Detail

evaluate

public abstract double evaluate(DoubleValues[] functionValues)

Evaluates the expression for the current document.

Parameters:

functionValues - DoubleValues for each element of variables.

Returns:

The computed value of the expression for the given document.

getDoubleValuesSource

public DoubleValuesSource getDoubleValuesSource(Bindings bindings)

Get a DoubleValuesSource which can compute the value of this expression in the context of the given bindings.

Parameters:

bindings - Bindings to use for external values in this expression

Returns:

A DoubleValuesSource which will evaluate this expression when used

getSortField

public SortField getSortField(Bindings bindings,
                              boolean reverse)

Get a sort field which can be used to rank documents by this expression.

getRescorer

public Rescorer getRescorer(Bindings bindings)

Get a Rescorer, to rescore first-pass hits using this expression.