Class AbstractFirstPassGroupingCollector<GROUP_VALUE_TYPE>

  • Direct Known Subclasses:
    TermFirstPassGroupingCollector

    public abstract class AbstractFirstPassGroupingCollector<GROUP_VALUE_TYPE>
    extends Collector
    FirstPassGroupingCollector is the first of two passes necessary to collect grouped hits. This pass gathers the top N sorted groups. Concrete subclasses define what a group is and how it is internally collected.

    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.
    • Constructor Detail

      • AbstractFirstPassGroupingCollector

        public AbstractFirstPassGroupingCollector​(Sort groupSort,
                                                  int topNGroups)
                                           throws IOException
        Create the first pass collector.
        Parameters:
        groupSort - The Sort 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.
        Throws:
        IOException - If I/O related errors occur
    • Method Detail

      • getTopGroups

        public Collection<SearchGroup<GROUP_VALUE_TYPE>> getTopGroups​(int groupOffset,
                                                                      boolean fillFields)
        Returns top groups, starting from offset. This may return null, if no groups were collected, or if the number of unique groups collected is <= offset.
        Parameters:
        groupOffset - The offset in the collected groups
        fillFields - Whether to fill to SearchGroup.sortValues
        Returns:
        top groups, starting from offset
      • 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) or IndexReader.document(int) on every hit. Doing so can slow searches by an order of magnitude or more.

        Specified by:
        collect in class Collector
        Throws:
        IOException
      • acceptsDocsOutOfOrder

        public boolean acceptsDocsOutOfOrder()
        Description copied from class: Collector
        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).

        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.

        Specified by:
        acceptsDocsOutOfOrder in class Collector
      • getDocGroupValue

        protected abstract GROUP_VALUE_TYPE getDocGroupValue​(int doc)
        Returns the group value for the specified doc.
        Parameters:
        doc - The specified doc
        Returns:
        the group value for the specified doc
      • copyDocGroupValue

        protected abstract GROUP_VALUE_TYPE copyDocGroupValue​(GROUP_VALUE_TYPE groupValue,
                                                              GROUP_VALUE_TYPE reuse)
        Returns a copy of the specified group value by creating a new instance and copying the value from the specified groupValue in the new instance. Or optionally the reuse argument can be used to copy the group value in.
        Parameters:
        groupValue - The group value to copy
        reuse - Optionally a reuse instance to prevent a new instance creation
        Returns:
        a copy of the specified group value