Nhibernate - partial loading of objects

Question

I have a MenuObject class that represents a websites Top Menu.

This object has amongst other properties, the following:

public class MenuObject
{
    public virtual int Id { get; set; }
    public virtual string Title { get; set; }
    public virtual List<MenuObject> Children { get; set; }
}

The mapping has been configured to eagerly load the Children objects using the Not.LazyLoad() definition in fluent nhibernate.

I now have a problem where I want to use these objects to populate a breadcrumb control and a sidemenu control - For these controls, All I need is:

The ID and Title Properties
The Children collection (also only containing the above two properties)

I don't want to load ALL the properties of my main object as well as ALL the properties of eachchild object as it's just overkill.

I've managed to use Nhibernate Linq to retrurn ONLY properties of the main object, but how do I amend the query to do the same for child objects? (see ???)

return (from mnu in session.Query<MenuObject>()
       (select new MenuObject()
{
    Id = mnu.Id
    Title = mnu.Title,
    Children = ???
}

----------------EDIT---------------------

I've got this to work but I'm missing a where clause - this is setting the 'Children' to a list of all MenuObject instances regardless of relationship - obviously I only want it to add legitimate child objects to each parent object - can anyone assist? Thanks

from menuobject in session
    .Query<MenuObject>()
    where menuobject.Level == level
    select new MenuObject()
    {
        Title = menuobject.Title,
        Url = menuobject.Url,
        Children = session.CreateCriteria<MenuObject>()
                          .SetProjection(Projections.ProjectionList()
                          .Add(Projections.Property("Title"), "Title")
                          .Add(Projections.Property("Url"), "Url"))
                          .SetResultTransformer(Transformers.AliasToBean(typeof (MenuObject)))
                          .List<MenuObject>()
    }
    .ToList();

Firo · Accepted Answer · 2012-01-31 07:46:49Z

1

sorry i missed the multiple childs part. Also i would favor ViewModels or anonymous types instead of partial loaded Domainobjects which could cause confusion down the road.

var results = (from mnu in session.Query<MenuObject>()
               from ch in mnu.Children
               select new
               {
                   mnu.Id,
                   mnu.Title,
                   ChildTitle = ch.Title,
                   ch.Url
               }).AsEnumerable()
               .GroupBy(row => new { row.Id, row.Title })
               .Select(gr => new
               {
                   gr.Key.Id,
                   gr.Key.Title,
                   Children = gr.Select(c => new { c.ChildTitle, c.Url }).ToList()
               });

edited Jan 31, 2012 at 7:46

answered Jan 30, 2012 at 14:34

Firo

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4 Comments

user1162591 Over a year ago

Thanks - however your answer appears to set the property 'Children' to a single instance of my object - 'Children' is actually a List<MenuObject> - I've tried this but with no luck

user1162591 Over a year ago

I've figured it out as above, but just need some assistance filtering out the child objects

user1162591 Over a year ago

Thanks for the answer and the tip; Are there any examples of using ViewModels about?

Firo Over a year ago

viewmodels are just classes which have the relevant data for the view they are used in, nothing fancy

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