c# Lucene search - build index

public class LuceneService : ILuceneService
{
    // Note there are many different types of Analyzer that may be used with Lucene, the exact one you use
    // will depend on your requirements
    private Analyzer analyzer = new WhitespaceAnalyzer(); 
    private Directory luceneIndexDirectory;
    private IndexWriter writer;
    private string indexPath = @"c:\temp\LuceneIndex";

    public LuceneService()
    {
        InitialiseLucene();
    }

    private void InitialiseLucene()
    {
        if(System.IO.Directory.Exists(indexPath))
        {
            System.IO.Directory.Delete(indexPath,true);
        }

        luceneIndexDirectory = FSDirectory.GetDirectory(indexPath);
        writer = new IndexWriter(luceneIndexDirectory, analyzer, true);
    }

    public void BuildIndex(IEnumerable<SampleDataFileRow> dataToIndex)
    {
        foreach (var sampleDataFileRow in dataToIndex)
	    {
		    Document doc = new Document();
            doc.Add(new Field("LineNumber", 
			sampleDataFileRow.LineNumber.ToString() , 
			Field.Store.YES, 
			Field.Index.UN_TOKENIZED));
            doc.Add(new Field("LineText", 
			sampleDataFileRow.LineText, 
			Field.Store.YES, 
			Field.Index.TOKENIZED));
            writer.AddDocument(doc);
	    }
        writer.Optimize();
        writer.Flush();
        writer.Close();
        luceneIndexDirectory.Close();
    }


    ....
    ....
    ....
    ....
    ....
}