ASP.NET 全文搜索

最近做一个在线阅读的网站文本内容的全文搜索网站(aspnet+sqlserver)，当时有两个方案：1. Sql server 2005 Full Text Search service。2. Lucene.Net。

Sql server的全文搜索索引管理比较方便，sqlserver 会自己管理索引的更新工作，也支持并发查询，但是遗憾的是没有HitHighlight功能，而且中文分词也做的比较瞎。

Lucene.NET的功能就比较全了，可惜自带的SimpleAnalyzer中文分词也比较瞎，就是把每个字拆开，还好有IkAnalyzer，分词效果还不错，中科院也个有分词系统听说做的不错（SharpICTCLAS），可是索引更新以及并发查询就是问题了。

综合一下，采用折中方案，索引以及查询用sql server做，查出结果后，用Lucene.NET里的HitHighlight对结果做命中高亮显示。

-- SP to search on the full text index with paging.

CREATE PROCEDURE [dbo].[SearchOnPageContent](@SearchTerm nvarchar(200),@startIndex INT,@pageSize INT)
AS
SELECT 
COUNT([key])
FROM 
CONTAINSTABLE(
Page,
PageContent,
@SearchTerm,
2052)
WHERE [RANK] > 0;

WITH tmp(id,pagenumber,pagecontent,[rank],seq) AS
(
select 
[key] AS id,
dbo.Page.PageNumber,
page.PageContent,
T.[rank],
ROW_NUMBER() OVER (ORDER BY T.[rank] DESC)
FROM 
CONTAINSTABLE(
Page,
PageContent,
@SearchTerm,
2052)AS T
JOIN PAGE ON PAGE.id = T.[key]
where t.[rank] > 0 
)
    
SELECT * FROM tmp WHERE seq BETWEEN (@startIndex -1)*@pageSize AND @startIndex *@pageSize
GO

// Class to handle hithighlight

using IKAnalyzerNet;
using Lucene.Net.QueryParsers;
using Lucene.Net.Search;

namespace OnlineReader.HitHighlight
{
    // User HitHighlight component to cite the hits terms.

    public class HitHighlighter
    {
        static IKAnalyzer analyzer = new IKAnalyzer();

        static QueryParser parser = new QueryParser("text", analyzer);

        private Query query = null;

        //static Lucene.Net.Search.IndexSearcher searcher = null;

        public string HitHighlight(string hitString,string searchTerm)
        {           
            query = parser.Parse(searchTerm);

            Lucene.Net.Highlight.Formatter formatter = new Lucene.Net.Highlight.SimpleHTMLFormatter("<span class='hit'> ", "</span>");

            Lucene.Net.Highlight.SimpleFragmenter fragmenter = new Lucene.Net.Highlight.SimpleFragmenter(400);
            Lucene.Net.Highlight.QueryScorer scorer = new Lucene.Net.Highlight.QueryScorer(query);
            Lucene.Net.Highlight.Highlighter highlighter = new Lucene.Net.Highlight.Highlighter(formatter, scorer);
            highlighter.SetTextFragmenter(fragmenter);

            Lucene.Net.Analysis.TokenStream stream = analyzer.TokenStream("", new System.IO.StringReader(hitString));
            string highlighted_text = highlighter.GetBestFragments(stream, hitString, 1, "...");

            if (highlighted_text == "") // someties the highlighter fails to emit text...
            {
                highlighted_text = hitString.Replace("'", "''");
            }
            if (highlighted_text.Length > 3000)
            {
                highlighted_text = highlighted_text.Substring(0, 3000);
            }
            return highlighted_text;
        }
    }
}