org.apache.lucene.search.join

Class ToParentBlockJoinCollector

java.lang.Object

org.apache.lucene.search.join.ToParentBlockJoinCollector

All Implemented Interfaces:

Collector

public class ToParentBlockJoinCollector
extends Object
implements Collector

Collects parent document hits for a Query containing one more more BlockJoinQuery clauses, sorted by the specified parent Sort. Note that this cannot perform arbitrary joins; rather, it requires that all joined documents are indexed as a doc block (using IndexWriter.addDocuments(java.lang.Iterable<? extends java.lang.Iterable<? extends org.apache.lucene.index.IndexableField>>) or IndexWriter.updateDocuments(org.apache.lucene.index.Term, java.lang.Iterable<? extends java.lang.Iterable<? extends org.apache.lucene.index.IndexableField>>)). Ie, the join is computed at index time.

This collector MUST be used with ToParentBlockJoinIndexSearcher, in order to work correctly.

The parent Sort must only use fields from the parent documents; sorting by field in the child documents is not supported.

You should only use this collector if one or more of the clauses in the query is a ToParentBlockJoinQuery. This collector will find those query clauses and record the matching child documents for the top scoring parent documents.

Multiple joins (star join) and nested joins and a mix of the two are allowed, as long as in all cases the documents corresponding to a single row of each joined parent table were indexed as a doc block.

For the simple star join you can retrieve the TopGroups instance containing each ToParentBlockJoinQuery's matching child documents for the top parent groups, using getTopGroups(org.apache.lucene.search.join.ToParentBlockJoinQuery, org.apache.lucene.search.Sort, int, int, int, boolean). Ie, a single query, which will contain two or more ToParentBlockJoinQuery's as clauses representing the star join, can then retrieve two or more TopGroups instances.

For nested joins, the query will run correctly (ie, match the right parent and child documents), however, because TopGroups is currently unable to support nesting (each group is not able to hold another TopGroups), you are only able to retrieve the TopGroups of the first join. The TopGroups of the nested joins will not be correct. See org.apache.lucene.search.join for a code sample.

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

Constructor Summary

Constructors

Constructor and Description
ToParentBlockJoinCollector(Sort sort, int numParentHits, boolean trackScores, boolean trackMaxScore) Creates a ToParentBlockJoinCollector.

Method Summary

Methods

Modifier and Type	Method and Description
LeafCollector	getLeafCollector(LeafReaderContext context)
float	getMaxScore() Returns the highest score across all collected parent hits, as long as trackMaxScores=true was passed on construction.
TopGroups<Integer>	getTopGroups(ToParentBlockJoinQuery query, Sort withinGroupSort, int offset, int maxDocsPerGroup, int withinGroupOffset, boolean fillSortFields) Returns the TopGroups for the specified BlockJoinQuery.
TopGroups<Integer>	getTopGroupsWithAllChildDocs(ToParentBlockJoinQuery query, Sort withinGroupSort, int offset, int withinGroupOffset, boolean fillSortFields) Returns the TopGroups for the specified BlockJoinQuery.
boolean	needsScores()

Methods inherited from class java.lang.Object

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

Constructor Detail

ToParentBlockJoinCollector

public ToParentBlockJoinCollector(Sort sort,
                          int numParentHits,
                          boolean trackScores,
                          boolean trackMaxScore)
                           throws IOException

Creates a ToParentBlockJoinCollector. The provided sort must not be null. If you pass true trackScores, all ToParentBlockQuery instances must not use ScoreMode.None.

Throws:

IOException

Method Detail

getLeafCollector

public LeafCollector getLeafCollector(LeafReaderContext context)
                               throws IOException

Specified by:

getLeafCollector in interface Collector

Throws:

IOException

getTopGroups

public TopGroups<Integer> getTopGroups(ToParentBlockJoinQuery query,
                              Sort withinGroupSort,
                              int offset,
                              int maxDocsPerGroup,
                              int withinGroupOffset,
                              boolean fillSortFields)
                                throws IOException

Returns the TopGroups for the specified BlockJoinQuery. The groupValue of each GroupDocs will be the parent docID for that group. The number of documents within each group is calculated as minimum of maxDocsPerGroup and number of matched child documents for that group. Returns null if no groups matched.

Parameters:

query - Search query

withinGroupSort - Sort criteria within groups

offset - Parent docs offset

maxDocsPerGroup - Upper bound of documents per group number

withinGroupOffset - Offset within each group of child docs

fillSortFields - Specifies whether to add sort fields or not

Returns:

TopGroups for specified query

Throws:

IOException - if there is a low-level I/O error

getTopGroupsWithAllChildDocs

public TopGroups<Integer> getTopGroupsWithAllChildDocs(ToParentBlockJoinQuery query,
                                              Sort withinGroupSort,
                                              int offset,
                                              int withinGroupOffset,
                                              boolean fillSortFields)
                                                throws IOException

Returns the TopGroups for the specified BlockJoinQuery. The groupValue of each GroupDocs will be the parent docID for that group. The number of documents within each group equals to the total number of matched child documents for that group. Returns null if no groups matched.

Parameters:

query - Search query

withinGroupSort - Sort criteria within groups

offset - Parent docs offset

withinGroupOffset - Offset within each group of child docs

fillSortFields - Specifies whether to add sort fields or not

Returns:

TopGroups for specified query

Throws:

IOException - if there is a low-level I/O error

getMaxScore

public float getMaxScore()

Returns the highest score across all collected parent hits, as long as trackMaxScores=true was passed on construction. Else, this returns Float.NaN

needsScores

public boolean needsScores()

Specified by:

needsScores in interface Collector