Generic Filter and Sort Using NHibernate

Question

Is there a way to implement Generic filter for NHibernate on a repository layer? As per Microsoft API Guidelines, the sort and filters are passed as string API Guidelines. what will be the approach to that using NHibernate to make it generic?

Answer 1

Please have a look at this post.There is a section Paging with NHibernate. The code snippet below is from this post.

The approach is to implement a class (in the post it was PagedResult<T>) in your case FilteredResult<T>. Having this class you can implementan extension (in post was NHibernatePagedResultExtensions) in this case NHibernateFilteredResultExtensions.

And the last thing left is to apply this extansion exacly the same way. Hope this will help.

public abstract class PagedResultBase
{
    public int CurrentPage { get; set; }

    public int PageCount { get; set; }

    public int PageSize { get; set; }

    public int RowCount { get; set; }
    public string LinkTemplate { get; set; }

    public int FirstRowOnPage
    {

        get { return (CurrentPage - 1) * PageSize + 1; }
    }

    public int LastRowOnPage
    {
        get { return Math.Min(CurrentPage * PageSize, RowCount); }
    }
}

public class PagedResult<T> : PagedResultBase
{
    public IList<T> Results { get; set; }

    public PagedResult()
    {
        Results = new List<T>();
    }
}


public static class NHibernatePagedResultExtensions
{
    public static async Task<PagedResult<T>> GetPagedAsync<T>(this IQueryable<T> query, int page, int pageSize)
    {
        var result = new PagedResult<T>
        {
            CurrentPage = page,
            PageSize = pageSize,
            RowCount = query.Count()
        };

        var pageCount = (double)result.RowCount / pageSize;
        result.PageCount = (int)Math.Ceiling(pageCount);

        var skip = (page - 1) * pageSize;
        result.Results = await query.Skip(skip).Take(pageSize).ToListAsync();

        return result;
    }
}



public async Task<IActionResult> Index(int page = 1)
{
    var result = await _session.RunInTransaction(async () =>
    {
        var books = await _session.Books
                                    .Where(b => b.Title.StartsWith("How to"))
                                    .GetPagedAsync(page, pageSize: 25);
        return _mapper.Map<PagedResult<BookModel>>(books);
    });

    return View(result);
}