Class ToParentBlockJoinCollector
- java.lang.Object
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- org.apache.lucene.search.Collector
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- org.apache.lucene.search.join.ToParentBlockJoinCollector
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public class ToParentBlockJoinCollector extends 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 (usingIndexWriter.addDocuments(java.util.Collection<org.apache.lucene.document.Document>)
orIndexWriter.updateDocuments(org.apache.lucene.index.Term, java.util.Collection<org.apache.lucene.document.Document>)
). Ie, the join is computed at index time.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 eachToParentBlockJoinQuery
's matching child documents for the top parent groups, usinggetTopGroups(org.apache.lucene.search.join.ToParentBlockJoinQuery, org.apache.lucene.search.Sort, int, int, int, boolean)
. Ie, a single query, which will contain two or moreToParentBlockJoinQuery
's as clauses representing the star join, can then retrieve two or moreTopGroups
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.
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Constructor Summary
Constructors Constructor Description ToParentBlockJoinCollector(Sort sort, int numParentHits, boolean trackScores, boolean trackMaxScore)
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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 parentDoc)
Called once for every document matching a query, with the unbased document number.TopGroups<Integer>
getTopGroups(ToParentBlockJoinQuery query, Sort withinGroupSort, int offset, int maxDocsPerGroup, int withinGroupOffset, boolean fillSortFields)
Return the TopGroups for the specified BlockJoinQuery.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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ToParentBlockJoinCollector
public ToParentBlockJoinCollector(Sort sort, int numParentHits, boolean trackScores, boolean trackMaxScore) throws IOException
- Throws:
IOException
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Method Detail
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collect
public void collect(int parentDoc) 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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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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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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setScorer
public void setScorer(Scorer scorer)
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.
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getTopGroups
public TopGroups<Integer> getTopGroups(ToParentBlockJoinQuery query, Sort withinGroupSort, int offset, int maxDocsPerGroup, int withinGroupOffset, boolean fillSortFields) throws IOException
Return the TopGroups for the specified BlockJoinQuery. The groupValue of each GroupDocs will be the parent docID for that group. Note that theGroupDocs.totalHits
, which would be the total number of child documents matching that parent, is not computed (will always be 0). Returns null if no groups matched.- Throws:
IOException
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