Package org.apache.lucene.search.join

Class ToParentBlockJoinQuery

  • All Implemented Interfaces:
    Serializable, Cloneable
    public class ToParentBlockJoinQuery
extends Query
    This query requires that you index children and parent docs as a single block, using the 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>) API. In each block, the child documents must appear first, ending with the parent document. At search time you provide a Filter identifying the parents, however this Filter must provide an FixedBitSet per sub-reader.

    WARNING: to create the parents filter, always use RawTermFilter (so that the filter includes deleted docs), wrapped with CachingWrapperFilter (so that the returned bit set per reader is a FixedBitSet), specifying DeletesMode.IGNORE (so that on reopen, the filter still includes deleted docs). Failure to do this can result in completely wrong documents being returned! For example: 

       Filter parents = new CachingWrapperFilter(
                          new RawTermFilter(new Term("parent", "yes")),
                          CachingWrapperFilter.DeletesMode.IGNORE);

    Once the block index is built, use this query to wrap any sub-query matching only child docs and join matches in that child document space up to the parent document space. You can then use this Query as a clause with other queries in the parent document space.

    See ToChildBlockJoinQuery if you need to join in the reverse order.

    The child documents must be orthogonal to the parent documents: the wrapped child query must never return a parent document.

    If you'd like to retrieve TopGroups for the resulting query, use the ToParentBlockJoinCollector. Note that this is not necessary, ie, if you simply want to collect the parent documents and don't need to see which child documents matched under that parent, then you can use any collector.

    NOTE: If the overall query contains parent-only matches, for example you OR a parent-only query with a joined child-only query, then the resulting collected documents will be correct, however the TopGroups you get from ToParentBlockJoinCollector will not contain every child for parents that had matched.

    See org.apache.lucene.search.join for an overview.

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

    • Constructor Detail

      • ToParentBlockJoinQuery

        public ToParentBlockJoinQuery​(Query childQuery,
                              Filter parentsFilter,
                              ToParentBlockJoinQuery.ScoreMode scoreMode)
        Create a ToParentBlockJoinQuery.
        Parameters:
        childQuery - Query matching child documents.
        parentsFilter - Filter (must produce FixedBitSet per-seegment) identifying the parent documents.
        scoreMode - How to aggregate multiple child scores into a single parent score.

    • Method Detail

      • createWeight

        public Weight createWeight​(Searcher searcher)
                    throws IOException
        Description copied from class: Query
        Expert: Constructs an appropriate Weight implementation for this query.

        Only implemented by primitive queries, which re-write to themselves.

        Overrides:
        createWeight in class Query
        Throws:
        IOException

      • extractTerms

        public void extractTerms​(Set<Term> terms)
        Description copied from class: Query
        Expert: adds all terms occurring in this query to the terms set. Only works if this query is in its rewritten form.
        Overrides:
        extractTerms in class Query

      • rewrite

        public Query rewrite​(IndexReader reader)
              throws IOException
        Description copied from class: Query
        Expert: called to re-write queries into primitive queries. For example, a PrefixQuery will be rewritten into a BooleanQuery that consists of TermQuerys.
        Overrides:
        rewrite in class Query
        Throws:
        IOException

      • toString

        public String toString​(String field)
        Description copied from class: Query
        Prints a query to a string, with field assumed to be the default field and omitted.

        The representation used is one that is supposed to be readable by QueryParser. However, there are the following limitations:

        • If the query was created by the parser, the printed representation may not be exactly what was parsed. For example, characters that need to be escaped will be represented without the required backslash.
        • Some of the more complicated queries (e.g. span queries) don't have a representation that can be parsed by QueryParser.
        Specified by:
        toString in class Query

      • equals

        public boolean equals​(Object _other)
        Overrides:
        equals in class Query

      • hashCode

        public int hashCode()
        Overrides:
        hashCode in class Query

      • clone

        public Object clone()
        Description copied from class: Query
        Returns a clone of this query.
        Overrides:
        clone in class Query