Question

public class Category
{
    public virtual int Id { set; get; }
    public virtual string Name { set; get; }
    public virtual int CategoryOrder { set; get; }
    public virtual IEnumerable<News> LatestNews { set; get; }
}

public sealed class CategoryMap :ClassMap<Category>
{

    public CategoryMap()
    {
        LazyLoad();
        Id(x => x.Id);
        Map(x => x.Name);
        Map(x => x.CategoryOrder);
        HasMany(x => x.LatestNews);
    }

}

        IRepository<Category> newsRepo = new NHibernateRepository<Category>();

        using(var session = newsRepo.GetSessionFactory().OpenSession())
        using(var transaction = session.BeginTransaction())
        {
            var result = session.Query<Category>().OrderBy(x => x.CategoryOrder);
            transaction.Commit();
        }

I have this category class Which I want to display a (only one) News per category. Is this correct mapping? or should i change it to Map

When i run this, it gets all the news per category. But i want the latest news per category (only one). I can get the latest news by querying News.DateUpdated.

How should i change the query to get one news per category?

or how do I get some of the News? ie: limit the number of news I can query?

Answer 1

I think you can have your cake and eat it too. You have a list of News items, so just leave that. But add in another property that gets just the News item you want.

public class Category
{
    public virtual int Id { set; get; }
    public virtual string Name { set; get; }
    public virtual int CategoryOrder { set; get; }
    public virtual IEnumerable<News> AllNews { set; get; }
    public virtual News LatestNews 
    {
        get
        {
            // probably needs some work
            return this.AllNews.OrderByDescending(n => n.SomeDateField).Take(1);
        }
    }
}

public sealed class CategoryMap :ClassMap<Category>
{

    public CategoryMap()
    {
        LazyLoad();
        Id(x => x.Id);
        Map(x => x.Name);
        Map(x => x.CategoryOrder);
        HasMany(x => x.AllNews);
    }

}