Class BlockGroupingCollector
- java.lang.Object
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- org.apache.lucene.search.Collector
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- org.apache.lucene.search.grouping.BlockGroupingCollector
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public class BlockGroupingCollector extends Collector
BlockGroupingCollector performs grouping with a single pass collector, as long as you are grouping by a doc block field, ie all documents sharing a given group value were indexed as a doc block using the atomicIndexWriter.addDocuments(java.util.Collection<org.apache.lucene.document.Document>)
orIndexWriter.updateDocuments(org.apache.lucene.index.Term, java.util.Collection<org.apache.lucene.document.Document>)
API.This results in faster performance (~25% faster QPS) than the two-pass grouping collectors, with the tradeoff being that the documents in each group must always be indexed as a block. This collector also fills in TopGroups.totalGroupCount without requiring the separate
TermAllGroupsCollector
. However, this collector does not fill in the groupValue of each group; this field will always be null.NOTE: this collector makes no effort to verify the docs were in fact indexed as a block, so it's up to you to ensure this was the case.
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.
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Constructor Summary
Constructors Constructor Description BlockGroupingCollector(Sort groupSort, int topNGroups, boolean needsScores, Filter lastDocPerGroup)
Create the single pass collector.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description boolean
acceptsDocsOutOfOrder()
Returntrue
if this collector does not require the matching docIDs to be delivered in int sort order (smallest to largest) toCollector.collect(int)
.void
collect(int doc)
Called once for every document matching a query, with the unbased document number.TopGroups
getTopGroups(Sort withinGroupSort, int groupOffset, int withinGroupOffset, int maxDocsPerGroup, boolean fillSortFields)
Returns the grouped results.void
setNextReader(IndexReader reader, int docBase)
Called before collecting from each IndexReader.void
setScorer(Scorer scorer)
Called before successive calls toCollector.collect(int)
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Constructor Detail
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BlockGroupingCollector
public BlockGroupingCollector(Sort groupSort, int topNGroups, boolean needsScores, Filter lastDocPerGroup) throws IOException
Create the single pass collector.- Parameters:
groupSort
- TheSort
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.needsScores
- true if the collected documents require scores, either because relevance is included in the withinGroupSort or because you plan to pass true for either getSscores or getMaxScores togetTopGroups(org.apache.lucene.search.Sort, int, int, int, boolean)
lastDocPerGroup
- aFilter
that marks the last document in each group.- Throws:
IOException
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Method Detail
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getTopGroups
public TopGroups getTopGroups(Sort withinGroupSort, int groupOffset, int withinGroupOffset, int maxDocsPerGroup, boolean fillSortFields) throws IOException
Returns the grouped results. Returns null if the number of groups collected is <= groupOffset.NOTE: This collector is unable to compute the groupValue per group so it will always be null. This is normally not a problem, as you can obtain the value just like you obtain other values for each matching document (eg, via stored fields, via FieldCache, etc.)
- Parameters:
withinGroupSort
- TheSort
used to sort documents within each group. Passing null is allowed, to sort by relevance.groupOffset
- Which group to start fromwithinGroupOffset
- Which document to start from within each groupmaxDocsPerGroup
- How many top documents to keep within each group.fillSortFields
- If true then the Comparable values for the sort fields will be set- Throws:
IOException
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setScorer
public void setScorer(Scorer scorer) throws IOException
Description copied from class:Collector
Called before successive calls toCollector.collect(int)
. Implementations that need the score of the current document (passed-in toCollector.collect(int)
), should save the passed-in Scorer and call scorer.score() when needed.- Specified by:
setScorer
in classCollector
- Throws:
IOException
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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)
orIndexReader.document(int)
on every hit. Doing so can slow searches by an order of magnitude or more.- Specified by:
collect
in classCollector
- Throws:
IOException
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acceptsDocsOutOfOrder
public boolean acceptsDocsOutOfOrder()
Description copied from class:Collector
Returntrue
if this collector does not require the matching docIDs to be delivered in int sort order (smallest to largest) toCollector.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 theCollector
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 classCollector
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setNextReader
public void setNextReader(IndexReader reader, int docBase) throws IOException
Description copied from class:Collector
Called before collecting from each IndexReader. All doc ids inCollector.collect(int)
will correspond to reader. Add docBase to the current IndexReaders internal document id to re-base ids inCollector.collect(int)
.- Specified by:
setNextReader
in classCollector
- Parameters:
reader
- next IndexReader- Throws:
IOException
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