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java.lang.Object org.apache.lucene.search.Collector org.apache.lucene.search.join.BlockJoinCollector
public class BlockJoinCollector
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.util.Collection
or IndexWriter.updateDocuments(org.apache.lucene.index.Term, java.util.Collection
). 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 BlockJoinQuery
. 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 BlockJoinQuery
's
matching child documents for the top parent groups,
using getTopGroups(org.apache.lucene.search.join.BlockJoinQuery, org.apache.lucene.search.Sort, int, int, int, boolean)
. Ie,
a single query, which will contain two or more
BlockJoinQuery
'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.
Constructor Summary | |
---|---|
BlockJoinCollector(Sort sort,
int numParentHits,
boolean trackScores,
boolean trackMaxScore)
|
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 parentDoc)
Called once for every document matching a query, with the unbased document number. |
TopGroups<Integer> |
getTopGroups(BlockJoinQuery 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 to Collector.collect(int) . |
Methods inherited from class java.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
---|
public BlockJoinCollector(Sort sort, int numParentHits, boolean trackScores, boolean trackMaxScore) throws IOException
IOException
Method Detail |
---|
public void collect(int parentDoc) throws IOException
Collector
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.
collect
in class Collector
IOException
public void setNextReader(IndexReader reader, int docBase) throws IOException
Collector
Collector.collect(int)
will correspond to reader.
Add docBase to the current IndexReaders internal document id to re-base ids
in Collector.collect(int)
.
setNextReader
in class Collector
reader
- next IndexReader
IOException
public boolean acceptsDocsOutOfOrder()
Collector
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.
acceptsDocsOutOfOrder
in class Collector
public void setScorer(Scorer scorer)
Collector
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.
setScorer
in class Collector
public TopGroups<Integer> getTopGroups(BlockJoinQuery query, Sort withinGroupSort, int offset, int maxDocsPerGroup, int withinGroupOffset, boolean fillSortFields) throws IOException
GroupDocs.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.
IOException
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