What is the correct way to rebuild Lucene's index

Question

I have a forum like web application written in Asp.net MVC. I'm trying to implement Lucene.net as the search engine. When I build my index, every now and then I get exceptions related to Lucene not being able to rename the deletable file. I think it's because I empty the index every time I want to rebuild it. Here is the code that deals with indexing:

public class SearchService : ISearchService
{
    Directory   IndexFileLocation;
    IndexWriter Writer;
    IndexReader Reader; 
    Analyzer    Analyzer;

    public SearchService(String indexLocation)
    {
        IndexFileLocation = FSDirectory.GetDirectory(indexLocation, System.IO.Directory.Exists(indexLocation) == false);
        Reader            = IndexReader.Open(IndexFileLocation);
        Writer            = new IndexWriter(IndexFileLocation, Analyzer, IndexFileLocation.List().Length == 0);
        Analyzer          = new StandardAnalyzer();
    }

    public void ClearIndex()
    {
        var DocumentCount = Writer.DocCount();
        if (DocumentCount == 0)
            return;

        for (int i = 0; i < DocumentCount; i++)
            Reader.DeleteDocument(i);
    }

    public void AddToSearchIndex(ISearchableData Data)
    {
        Document Doc = new Document();

        foreach (var Entry in Data)
        {
            Field field = new Field(Entry.Key, 
                                    Entry.Value, 
                                    Lucene.Net.Documents.Field.Store.NO, 
                                    Lucene.Net.Documents.Field.Index.TOKENIZED, 
                                    Lucene.Net.Documents.Field.TermVector.WITH_POSITIONS_OFFSETS);
            Doc.Add(field);
        }

        Field KeyField = new Field(
            SearchField.Key.ToString(), 
            Data.Key, 
            Lucene.Net.Documents.Field.Store.YES, 
            Lucene.Net.Documents.Field.Index.NO);

        Doc.Add(KeyField);
        Writer.AddDocument(Doc);
    }

    public void Dispose()
    {
        Writer.Optimize();
        Writer.Close();
        Reader.Close();
    }
}

And here is the code that executes it all:

    private void btnRebuildIndex_Click(object sender, EventArgs e)
    {
        using (var SearchService = new SearchService(Application.StartupPath + @"\indexs\"))
        {
            SearchService.ClearIndex();
        }

        using (var SearchService = new SearchService(Application.StartupPath + @"\indexs\"))
        {
            Int32 BatchSize = 50;
            Int32 Current = 0;
            var TotalQuestions = SubmissionService.GetQuestionsCount();

            while (Current < TotalQuestions)
            {
                var Questions = SubmissionService.ListQuestions(Current, BatchSize, "Id", Qsparx.SortOrder.Asc);

                foreach (var Question in Questions)
                {
                    SearchService.AddToSearchIndex(Question.ToSearchableData());
                }

                Current += BatchSize;
            }
        }
    }

Why does Lucene complain about renaming the "deletable" file?

Answer 1

Not sure why you are recreating the index everytime. You can append to the index thus:

Writer = new IndexWriter(IndexFileLocation, Analyzer,false);

The false flag at the end tells the IndexWriter to open in append mode(i.e. not overwrite). That might make your problem go away.

Answer 2

It turned out, if no index files exist, then creating an IndexReader before an IndexWriter is not a good idea. I also realized even though the AddDocument method of IndexWriter has two overloads (one w/ and one w/o Analyzer parameter) only the one with analyzer parameter works for me.