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 usage:

   // 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, null, 10, sort);
 

See Also:

JavascriptCompiler.compile(java.lang.String)

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

Field Summary

String	sourceText The original source text
String[]	variables Named variables referred to by this expression

Constructor Summary

protected

Expression(String sourceText, String[] variables) Creates a new Expression.

Method Summary

abstract double	evaluate(int document, FunctionValues[] functionValues) Evaluates the expression for the given document.
SortField	getSortField(Bindings bindings, boolean reverse) Get a sort field which can be used to rank documents by this expression.
ValueSource	getValueSource(Bindings bindings) Get a value source which can compute the value of this expression in the context of the given bindings.

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(int document,
                                FunctionValues[] functionValues)

Evaluates the expression for the given document.

Parameters:

document - docId of the document to compute a value for

functionValues - FunctionValues for each element of variables.

Returns:

The computed value of the expression for the given document.

getValueSource

public ValueSource getValueSource(Bindings bindings)

Get a value source 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 value source 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.