Package org.apache.lucene.search.join

Class ToParentBlockJoinCollector

  • public class ToParentBlockJoinCollector
extends org.apache.lucene.search.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.util.Collection<org.apache.lucene.document.Document>) or IndexWriter.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 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 Detail

      • ToParentBlockJoinCollector

        public ToParentBlockJoinCollector​(org.apache.lucene.search.Sort sort,
                                  int numParentHits,
                                  boolean trackScores,
                                  boolean trackMaxScore)
                           throws IOException
        Throws:
        IOException

    • Method Detail

      • collect

        public void collect​(int parentDoc)
             throws IOException
        Specified by:
        collect in class org.apache.lucene.search.Collector
        Throws:
        IOException

      • setNextReader

        public void setNextReader​(org.apache.lucene.index.IndexReader reader,
                          int docBase)
                   throws IOException
        Specified by:
        setNextReader in class org.apache.lucene.search.Collector
        Throws:
        IOException

      • acceptsDocsOutOfOrder

        public boolean acceptsDocsOutOfOrder()
        Specified by:
        acceptsDocsOutOfOrder in class org.apache.lucene.search.Collector

      • setScorer

        public void setScorer​(org.apache.lucene.search.Scorer scorer)
        Specified by:
        setScorer in class org.apache.lucene.search.Collector

      • getTopGroups

        public org.apache.lucene.search.grouping.TopGroups<Integer> getTopGroups​(ToParentBlockJoinQuery query,
                                                                         org.apache.lucene.search.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 the 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.
        Throws:
        IOException