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Date: Fri, 21 Aug 2009 07:17:14 -0700 (PDT)
From: "Tim Smith (JIRA)" <jira@apache.org>
To: java-dev@lucene.apache.org
Subject: [jira] Commented: (LUCENE-1821) Weight.scorer() not passed doc
 offset for "sub reader"
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    [ https://issues.apache.org/jira/browse/LUCENE-1821?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12745988#action_12745988 ] 

Tim Smith commented on LUCENE-1821:
-----------------------------------

here's what you can do:

{code}
  /** @deprecated use {@link getDocIdSet(IndexSearcher, IndexReader)} */
  public DocIdSet getDocIdSet(final IndexReader reader) throws IOException {
    return getDocIdSet(new IndexSearcher(reader), reader);
  }

  public DocIdSet getDocIdSet(final IndexSearcher searcher, final IndexReader reader) {
    final Weight weight = query.weight(searcher);
    return new DocIdSet() {
      public DocIdSetIterator iterator() throws IOException {
        return weight.scorer(searcher, reader, true, false);
      }
    };
  }
{code}

and yeah, i'm all for tons warnings in javadoc explicitly defining the contracts


> Weight.scorer() not passed doc offset for "sub reader"
> ------------------------------------------------------
>
>                 Key: LUCENE-1821
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1821
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Search
>    Affects Versions: 2.9
>            Reporter: Tim Smith
>             Fix For: 2.9
>
>         Attachments: LUCENE-1821.patch
>
>
> Now that searching is done on a per segment basis, there is no way for a Scorer to know the "actual" doc id for the document's it matches (only the relative doc offset into the segment)
> If using caches in your scorer that are based on the "entire" index (all segments), there is now no way to index into them properly from inside a Scorer because the scorer is not passed the needed offset to calculate the "real" docid
> suggest having Weight.scorer() method also take a integer for the doc offset
> Abstract Weight class should have a constructor that takes this offset as well as a method to get the offset
> All Weights that have "sub" weights must pass this offset down to created "sub" weights
> Details on workaround:
> In order to work around this, you must do the following:
> * Subclass IndexSearcher
> * Add "int getIndexReaderBase(IndexReader)" method to your subclass
> * during Weight creation, the Weight must hold onto a reference to the passed in Searcher (casted to your sub class)
> * during Scorer creation, the Scorer must be passed the result of YourSearcher.getIndexReaderBase(reader)
> * Scorer can now rebase any collected docids using this offset
> Example implementation of getIndexReaderBase():
> {code}
> // NOTE: more efficient implementation can be done if you cache the result if gatherSubReaders in your constructor
> public int getIndexReaderBase(IndexReader reader) {
>   if (reader == getReader()) {
>     return 0;
>   } else {
>     List readers = new ArrayList();
>     gatherSubReaders(readers);
>     Iterator iter = readers.iterator();
>     int maxDoc = 0;
>     while (iter.hasNext()) {
>       IndexReader r = (IndexReader)iter.next();
>       if (r == reader) {
>         return maxDoc;
>       } 
>       maxDoc += r.maxDoc();
>     } 
>   }
>   return -1; // reader not in searcher
> }
> {code}
> Notes:
> * This workaround makes it so you cannot serialize your custom Weight implementation

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