org.apache.lucene.search.join

Class JoinUtil

java.lang.Object

org.apache.lucene.search.join.JoinUtil

public final class JoinUtil
extends Object

Utility for query time joining using TermsQuery and TermsCollector.

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

Method Summary

Methods

Modifier and Type	Method and Description
static Query	createJoinQuery(String fromField, boolean multipleValuesPerDocument, String toField, Query fromQuery, IndexSearcher fromSearcher, ScoreMode scoreMode) Method for query time joining.

Methods inherited from class java.lang.Object

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

Method Detail

createJoinQuery

public static Query createJoinQuery(String fromField,
                    boolean multipleValuesPerDocument,
                    String toField,
                    Query fromQuery,
                    IndexSearcher fromSearcher,
                    ScoreMode scoreMode)
                             throws IOException

Method for query time joining.

Execute the returned query with a IndexSearcher to retrieve all documents that have the same terms in the to field that match with documents matching the specified fromQuery and have the same terms in the from field.

In the case a single document relates to more than one document the multipleValuesPerDocument option should be set to true. When the multipleValuesPerDocument is set to true only the the score from the first encountered join value originating from the 'from' side is mapped into the 'to' side. Even in the case when a second join value related to a specific document yields a higher score. Obviously this doesn't apply in the case that ScoreMode.None is used, since no scores are computed at all.

Memory considerations: During joining all unique join values are kept in memory. On top of that when the scoreMode isn't set to ScoreMode.None a float value per unique join value is kept in memory for computing scores. When scoreMode is set to ScoreMode.Avg also an additional integer value is kept in memory per unique join value.

Parameters:

fromField - The from field to join from

multipleValuesPerDocument - Whether the from field has multiple terms per document

toField - The to field to join to

fromQuery - The query to match documents on the from side

fromSearcher - The searcher that executed the specified fromQuery

scoreMode - Instructs how scores from the fromQuery are mapped to the returned query

Returns:

a Query instance that can be used to join documents based on the terms in the from and to field

Throws:

IOException - If I/O related errors occur