FieldScoreQuery

Class Overview

A query that scores each document as the value of the numeric input field.

The query matches all documents, and scores each document according to the numeric value of that field.

It is assumed, and expected, that:

• The field used here is indexed, and has exactly one token in every scored document.
• Best if this field is un_tokenized.
• That token is parseable to the selected type.

Combining this query in a FunctionQuery allows much freedom in affecting document scores. Note, that with this freedom comes responsibility: it is more than likely that the default Lucene scoring is superior in quality to scoring modified as explained here. However, in some cases, and certainly for research experiments, this capability may turn useful.

When constructing this query, select the appropriate type. That type should match the data stored in the field. So in fact the "right" type should be selected before indexing. Type selection has effect on the RAM usage:

• BYTE consumes 1 * maxDocs bytes.
• SHORT consumes 2 * maxDocs bytes.
• INT consumes 4 * maxDocs bytes.
• FLOAT consumes 8 * maxDocs bytes.

Caching: Values for the numeric field are loaded once and cached in memory for further use with the same IndexReader. To take advantage of this, it is extremely important to reuse index-readers or index-searchers, otherwise, for instance if for each query a new index reader is opened, large penalties would be paid for loading the field values into memory over and over again!

Summary

[Expand] Inherited Methods
From class org.apache.lucene.search.function.ValueSourceQuery Weight createWeight(Searcher searcher) Expert: Constructs an appropriate Weight implementation for this query. boolean equals(Object o) Returns true if o is equal to this. void extractTerms(Set<Term> terms) Expert: adds all terms occurring in this query to the terms set. int hashCode() Returns a hash code value for this object. Query rewrite(IndexReader reader) Expert: called to re-write queries into primitive queries. String toString(String field) Prints a query to a string, with field assumed to be the default field and omitted.
From class org.apache.lucene.search.Query Object clone() Returns a clone of this query. Query combine(Query[] queries) Expert: called when re-writing queries under MultiSearcher. Weight createWeight(Searcher searcher) Expert: Constructs an appropriate Weight implementation for this query. boolean equals(Object obj) void extractTerms(Set<Term> terms) Expert: adds all terms occurring in this query to the terms set. float getBoost() Gets the boost for this clause. @Deprecated Similarity getSimilarity(Searcher searcher) This method is deprecated. Instead of using "runtime" subclassing/delegation, subclass the Weight instead. int hashCode() static Query mergeBooleanQueries(BooleanQuery... queries) Expert: merges the clauses of a set of BooleanQuery's into a single BooleanQuery. Query rewrite(IndexReader reader) Expert: called to re-write queries into primitive queries. void setBoost(float b) Sets the boost for this query clause to b. String toString() Prints a query to a string. abstract String toString(String field) Prints a query to a string, with field assumed to be the default field and omitted. Weight weight(Searcher searcher) Expert: Constructs and initializes a Weight for a top-level query.
From class java.lang.Object Object clone() boolean equals(Object arg0) void finalize() final Class<?> getClass() int hashCode() final void notify() final void notifyAll() String toString() final void wait() final void wait(long arg0, int arg1) final void wait(long arg0)

Public Constructors