EF CTP4 lazy loading not playing ball

I'm using the CTP4 code first EF framework, but I'm having problems getting lazy loading to work. Reading up on it, it should be simple, but it's just not

public class Folder
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int? ParentFolderId { get; set; }

    public virtual IList<Folder> ChildFolders { get; set; }
}

In the model configuration:

HasMany(f => f.ChildFolders).WithOptional().HasConstraint((child, folder) => child.ParentFolderId == folder.Id);

However, when I do this:

Folder folder = context.Folders.SingleOr开发者_开发知识库Default(f => f.Id == 1);

folder.ChildPages is null....but it should be lazy loading it...

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I found the answer to this, actually: The empty constructor for "Folder" was marked internal, and although there were no hard failures, it seems this was enough to cause problems.

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Is your context based on DbContext or ObjectContext? If it is ObjectContext then you have to turn on lazy loading in ContextOptions.