org.apache.lucene.search.function
Class FieldScoreQuery

java.lang.Object
  org.apache.lucene.search.Query
      org.apache.lucene.search.function.ValueSourceQuery
          org.apache.lucene.search.function.FieldScoreQuery

All Implemented Interfaces:

Serializable, Cloneable

public class FieldScoreQuery
extends ValueSourceQuery

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:

• FieldScoreQuery.Type.BYTE consumes 1 * maxDocs bytes.
• FieldScoreQuery.Type.SHORT consumes 2 * maxDocs bytes.
• FieldScoreQuery.Type.INT consumes 4 * maxDocs bytes.
• FieldScoreQuery.Type.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!

See Also:

Serialized Form

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

Nested Class Summary

static class

FieldScoreQuery.Type Type of score field, indicating how field values are interpreted/parsed.

Constructor Summary

FieldScoreQuery(String field, FieldScoreQuery.Type type)
Create a FieldScoreQuery - a query that scores each document as the value of the numeric input field.

Method Summary

Methods inherited from class org.apache.lucene.search.function.ValueSourceQuery

createWeight, equals, extractTerms, hashCode, rewrite, toString

Methods inherited from class org.apache.lucene.search.Query

clone, combine, getBoost, getSimilarity, mergeBooleanQueries, setBoost, toString, weight

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

FieldScoreQuery

public FieldScoreQuery(String field,
                       FieldScoreQuery.Type type)

Create a FieldScoreQuery - a query that scores each document as the value of the numeric input field.

The type param tells how to parse the field string values into a numeric score value.

Parameters:

field - the numeric field to be used.

type - the type of the field: either FieldScoreQuery.Type.BYTE, FieldScoreQuery.Type.SHORT, FieldScoreQuery.Type.INT, or FieldScoreQuery.Type.FLOAT.