org.apache.lucene.search.grouping
Class FirstPassGroupingCollector

java.lang.Object
  org.apache.lucene.search.Collector
      org.apache.lucene.search.grouping.FirstPassGroupingCollector

public class FirstPassGroupingCollector
extends Collector

FirstPassGroupingCollector is the first of two passes necessary to collect grouped hits. This pass gathers the top N sorted groups.

See org.apache.lucene.search.grouping for more details including a full code example.

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

Constructor Summary

FirstPassGroupingCollector(String groupField, Sort groupSort, int topNGroups)
Create the first pass collector.

Method Summary

boolean	acceptsDocsOutOfOrder() Return true if this collector does not require the matching docIDs to be delivered in int sort order (smallest to largest) to Collector.collect(int).
void	collect(int doc) Called once for every document matching a query, with the unbased document number.
String	getGroupField()
Collection<SearchGroup>	getTopGroups(int groupOffset, boolean fillFields) Returns top groups, starting from offset.
void	setNextReader(IndexReader reader, int docBase) Called before collecting from each IndexReader.
void	setScorer(Scorer scorer) Called before successive calls to Collector.collect(int).

Methods inherited from class java.lang.Object

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

Constructor Detail

FirstPassGroupingCollector

public FirstPassGroupingCollector(String groupField,
                                  Sort groupSort,
                                  int topNGroups)
                           throws IOException

Create the first pass collector.

Parameters:

groupField - The field used to group documents. This field must be single-valued and indexed (FieldCache is used to access its value per-document).

groupSort - The Sort used to sort the groups. The top sorted document within each group according to groupSort, determines how that group sorts against other groups. This must be non-null, ie, if you want to groupSort by relevance use Sort.RELEVANCE.

topNGroups - How many top groups to keep.

Throws:

IOException

Method Detail

getTopGroups

public Collection<SearchGroup> getTopGroups(int groupOffset,
                                            boolean fillFields)

Returns top groups, starting from offset. This may return null, if no groups were collected, or if the number of unique groups collected is <= offset.

getGroupField

public String getGroupField()

setScorer

public void setScorer(Scorer scorer)
               throws IOException

Description copied from class: Collector

Called before successive calls to Collector.collect(int). Implementations that need the score of the current document (passed-in to Collector.collect(int)), should save the passed-in Scorer and call scorer.score() when needed.

Specified by:

setScorer in class Collector

Throws:

IOException

collect

public void collect(int doc)
             throws IOException

Description copied from class: Collector

Called once for every document matching a query, with the unbased document number.

Note: This is called in an inner search loop. For good search performance, implementations of this method should not call Searcher.doc(int) or IndexReader.document(int) on every hit. Doing so can slow searches by an order of magnitude or more.

Specified by:

collect in class Collector

Throws:

IOException

acceptsDocsOutOfOrder

public boolean acceptsDocsOutOfOrder()

Description copied from class: Collector

Return true if this collector does not require the matching docIDs to be delivered in int sort order (smallest to largest) to Collector.collect(int).

Most Lucene Query implementations will visit matching docIDs in order. However, some queries (currently limited to certain cases of BooleanQuery) can achieve faster searching if the Collector allows them to deliver the docIDs out of order.

Many collectors don't mind getting docIDs out of order, so it's important to return true here.

Specified by:

acceptsDocsOutOfOrder in class Collector

setNextReader

public void setNextReader(IndexReader reader,
                          int docBase)
                   throws IOException

Description copied from class: Collector

Called before collecting from each IndexReader. All doc ids in Collector.collect(int) will correspond to reader. Add docBase to the current IndexReaders internal document id to re-base ids in Collector.collect(int).

Specified by:

setNextReader in class Collector

Parameters:

reader - next IndexReader

Throws:

IOException