How to properly display List<class> in ComboBox, and make the value member point to the selected class object?

Question

I am developing simple prof of concept using C# winform , and Nhibernate as ORM,

its very simple just adding an item. and each item have a Foreign Key to Category table.

Sorry i couldnt upload image for the class diagram, i am not allowed yet to upload images. so the classes are

public class Category
{
    public virtual Guid Id { get; set; }
    public virtual string Name { get; set; }
    public virtual string NameArabic { get; set; }

    public static bool AddCategory(Category category)
    {
        using (var session=NhibernateHelper.OpenSession())
        {
            using (var transaction=session.BeginTransaction())
            {
                session.SaveOrUpdate(category);
                transaction.Commit();
            }
            return true;
        }
    }

    public static IList<Category> GetAll()
    {
        using (var session=NhibernateHelper.OpenSession())
        {
            return session.QueryOver<Category>().List<Category>();
        }
    }
}

public class Item
{
    public virtual Guid Id { get; set; }
    public virtual string Description { get; set; }

    public virtual Category Category { get; set; }

    public static bool AddItem(Item item)
    {
        using (var session = NhibernateHelper.OpenSession())
        {
            using (var transaction = session.BeginTransaction())
            {
                session.SaveOrUpdate(item);
                transaction.Commit();
            }
            return true;
        }
    }
}

When the users click insert item button it should execute the following code

    private void insertItem_Click(object sender, EventArgs e)
    {           
         Model.Item item = new Item
        {
         // allCategories is IList<Category> contain all categories retrieved from Database
            Category = (from category in allCategories 
                        where category.Id == Guid.Parse(comboBox1.SelectedValue.ToString())
                       select category).FirstOrDefault(),
            Description = textBox1.Text // the name text box
          };

        if (Model.Item.AddItem(item))
            MessageBox.Show("Transaction Completed");
    }

My problem is, since i am using Nhibernate and to avoid inserting new category in the database each time i add item , i should pass a category object with Guid as the same as the saved one in the database, so i used the linq query as shown above that queries on all categories list retrieved from the database which i think is bad approach.

is there suggestion to bind the allCategories List directly to the comboBox, in which i can use a specific property to point at the derived object Guid that currently listed in the comboBox.

Class Mapping

    public CategoryMap()
    {
        Id(x => x.Id);
        Map(x => x.Name);
        Map(x => x.NameArabic);
    }

    public ItemMap()
    {
        Id(x => x.Id);
        Map(x => x.Description);
        References(x => x.Category);
    }

Thanks,

Answer 1

Use this

YourComboBox.DataSource = YourList<Category>;
YourComboBox.DisplayMember = StringNameOfProperty;

to fill your Combobox. To get the item behind the Propery-Value use:

var item = (Category) YourComboBox.SelectedItem;