NHibernate不加载子对象

Question

I have following class and associated mappings (Fluent NHibernate):

public class Category
{
    public virtual int Id { get; set; }
    public virtual string Name { get; set; }
    public virtual string Description { get; set; }
    public virtual Category ParentCategory { get; set; }
    public virtual IList<Category> ChildCategories { get; set; }
}

Mappings:

public class CategoryMap : ClassMap<Category>
{
    public CategoryMap()
    {
        Table("Categories");

        Id(x => x.Id).Column("Id").CustomType("Int32").Access.Property()
         .CustomSqlType("int").Not.Nullable().Precision(10)
         .GeneratedBy.Identity();

        Map(x => x.Description).Column("Description").Nullable()
         .Generated.Never().CustomType(typeof (string)).Access
         .Property().Length(250);

        Map(x => x.Name).Not.Nullable().Generated.Never().CustomType("string")
         .Access.Property().Column("Name").Length(50);

        References(x => x.ParentCategory).Column("ParentCategoryId");
        HasMany(x => x.ChildCategories).KeyColumn("ParentCategoryId").Inverse()
         .AsBag().Fetch.Select();
    }
}

I creating two Category object as follows:

var c = new Category
        {
            Name = "Ebooks",
            Description = "Contains awz, mobi, pdf, epub and other 
                electronic books"
        };
var cc = new Category
         {
            Name = "Kindle Books",
            Description = "Contains Kindle ebook reader format books 
                    (awz, mobi)",
            ParentCategory = c
         };
session.SaveOrUpdate(c);
session.SaveOrUpdate(cc);

When I try to access saved objects:

var c = session.Load<Category>(1);
var cc = c.ChildCategories;

c contains the Category object with Id of 1 but its ChildCategories property is null .

What I am doing wrong?

PS:- This is my first experiment with NHibernate and so with Fluent NHibernate .

EDIT:- The following stuff worked. I needed to close the session before opening it again for reading. Otherwise it read just from memory nad as @Holf has pointed out I needed to add Child Category to Category like:

c.ChilCategories.Add(cc);

I just did as follows:

var session = sf.OpenSession();
CreateCategory(session);//ADDED TWO CATEGORIES EBooks, Kindle Ebooks
session.Close();

session = sf.OpenSession();
FetchCategories(session);//READ CATEGORY EBooks AND ASSOCIATED CHILDREN
session.Close();

Answer 1

Although you've handled one side of the relationship, by assigning 'c' as the ParentCategory of 'cc', I can't see anywhere that you've done the inverse. I think you'll also need to do

c.ChildCategories.Add(cc);

before doing the SaveOrUpdate.

Answer 2

Can you update your map to the following:

public class CategoryMap : ClassMap<Category>
{
    public CategoryMap()
    {
        Table("Categories");

        Id(x => x.Id).Column("Id").CustomType("Int32").Access.Property()
         .CustomSqlType("int").Not.Nullable().Precision(10)
         .GeneratedBy.Identity();

        Map(x => x.Description).Column("Description").Nullable()
         .Generated.Never().CustomType(typeof (string)).Access
         .Property().Length(250);

        Map(x => x.Name).Not.Nullable().Generated.Never().CustomType("string")
         .Access.Property().Column("Name").Length(50);

        References(x => x.ParentCategory).Column("ParentCategoryId");
        HasMany(x => x.ChildCategories).KeyColumn("ParentCategoryId").Inverse()
         .Cascade.All();
    }
}

Also you cannot be sure that the Id with value 1 refers to the Parent Category, use the LInq provider to load the correct object.