Class Expression

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

Inheritance
System.Object
Expression
Inherited Members
System.Object.Equals(System.Object)
System.Object.Equals(System.Object, System.Object)
System.Object.GetHashCode()
System.Object.GetType()
System.Object.MemberwiseClone()
System.Object.ReferenceEquals(System.Object, System.Object)
System.Object.ToString()
Namespace: Lucene.Net.Expressions
Assembly: Lucene.Net.Expressions.dll
Syntax
public abstract class Expression
Remarks

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", SortFieldType.SCORE));
bindings.Add(new SortField("popularity", SortFieldType.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);
Note

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

Constructors

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Expression(String, String[])

Creates a new Expression.

Declaration
public Expression(string sourceText, string[] variables)
Parameters
Type Name Description
System.String sourceText

Source text for the expression: e.g. ln(popularity)
System.String[] variables

Names of external variables referred to by the expression

Properties

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SourceText

The original source text

Declaration
public string SourceText { get; }
Property Value
Type Description
System.String
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Variables

Named variables referred to by this expression

Declaration
public string[] Variables { get; }
Property Value
Type Description
System.String[]

Methods

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Evaluate(Int32, FunctionValues[])

Evaluates the expression for the given document.

Declaration
public abstract double Evaluate(int document, FunctionValues[] functionValues)
Parameters
Type Name Description
System.Int32 document

docId of the document to compute a value for
Lucene.Net.Queries.Function.FunctionValues[] functionValues

Lucene.Net.Queries.Function.FunctionValues for each element of Variables.
Returns
Type Description
System.Double

The computed value of the expression for the given document.
Remarks

Evaluates the expression for the given document.

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GetRescorer(Bindings)

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

Declaration
public virtual Rescorer GetRescorer(Bindings bindings)
Parameters
Type Name Description
Bindings bindings
Returns
Type Description
Lucene.Net.Search.Rescorer
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GetSortField(Bindings, Boolean)

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

Declaration
public virtual SortField GetSortField(Bindings bindings, bool reverse)
Parameters
Type Name Description
Bindings bindings
System.Boolean reverse
Returns
Type Description
Lucene.Net.Search.SortField
Remarks

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

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GetValueSource(Bindings)

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

Declaration
public virtual ValueSource GetValueSource(Bindings bindings)
Parameters
Type Name Description
Bindings bindings

Bindings to use for external values in this expression
Returns
Type Description
Lucene.Net.Queries.Function.ValueSource

A value source which will evaluate this expression when used
Remarks

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

See Also