NHibernate 3.0 利用MultiCriteria进行分页

To display many forms and web pages, we need to run several queries. For example, it's 
common to display search results one page at a time. This typically requires two queries. The 
first counts all the available results, and the second fetches the data for only 10 or 20 results. 
MultiCriteria allows us to combine these two queries into a single database round 
trip, speeding up our application. In this recipe, I'll show you how to use MultiCriteria to 
fetch a paged result set of product

1.  Complete the setup steps in the introduction at the beginning of this chapter.

2.  Add the following structure inside the Queriesclass:

public struct PageOf<T>
{
     public int PageCount;
     public int PageNumber;
     public IEnumerable<T> PageOfResults;
}

3.  Add the following methods to the Queriesclass:

public PageOf<Product> GetPageOfProducts(
     int pageNumber,
     int pageSize)
{
     var skip = (pageNumber - 1) * pageSize;
     var countQuery = GetCountQuery();
     var resultQuery = GetPageQuery(skip, pageSize);
     var multiCrit = _session.CreateMultiCriteria().Add<int>("count", countQuery).Add<Product>("page", resultQuery);
     var productCount = ((IList<int>)multiCrit.GetResult("count")).Single();
     var products = (IList<Product>)multiCrit.GetResult("page");
     var pageCount = (int) Math.Ceiling(productCount/(double) pageSize);
     return new PageOf<Product>()
             {

                  PageCount = pageCount,
                  PageOfResults = products,
                  PageNumber = pageNumber
              };
}
private ICriteria GetCountQuery()
{
     return _session.QueryOver<Product>()
        .Select(list => list
        .SelectCount(m => m.Id))
        .UnderlyingCriteria;
}
private ICriteria GetPageQuery(int skip, int take)
{
     return _session.QueryOver<Product>()
         .OrderBy(m => m.UnitPrice).Asc
         .Skip(skip)
         .Take(take)
         .UnderlyingCriteria;
}

4.  In Program.cs, use the following code in the RunQueriesmethod:

static void RunQueries(ISession session)
{
     var queries = new Queries(session);
     var result = queries.GetPageOfProducts(1, 2);
     var heading = string.Format("Page {0} of {1}",
     result.PageNumber,result.PageCount);
     Show(heading, result.PageOfResults);
}

5.  Build and run your application. You should see the following output: