Question

Using NHibernate 3.2 ByCode configuration, I am attempting to map the following hierarchical entity:

public class BusinessType
{
    public virtual Guid BusinessTypeId { get; set; }
    public virtual Guid? ParentBusinessTypeId { get; set; }
    public virtual String BusinessTypeName { get; set; }
    public virtual ICollection<BusinessType> Children { get; set; }
}

with this ClassMapping:

public class BusinessTypeMapper : ClassMapping<BusinessType>
{
    public BusinessTypeMapper()
    {
        Id(x => x.BusinessTypeId, x => x.Type(new GuidType()));
        Property(x => x.ParentBusinessTypeId, x => x.Type(new GuidType()));
        Property(x => x.BusinessTypeName);
        Set(x => x.Children,
            cm =>
                {
                    // This works, but there is an ugly string in here
                    cm.Key(y => y.Column("ParentBusinessTypeId"));
                    cm.Inverse(true);
                    cm.OrderBy(bt => bt.BusinessTypeName);
                    cm.Lazy(CollectionLazy.NoLazy);
                },
            m => m.OneToMany());
    }
}

This works fine, but I’d rather be able to specify the key of the relation using a lambda so that refactoring works. This seems to be available, as follows:

public class BusinessTypeMapper : ClassMapping<BusinessType>
{
    public BusinessTypeMapper()
    {
        Id(x => x.BusinessTypeId, x => x.Type(new GuidType()));
        Property(x => x.ParentBusinessTypeId, x => x.Type(new GuidType()));
        Property(x => x.BusinessTypeName);
        Set(x => x.Children,
            cm =>
                {
                    // This compiles and runs, but generates some other column
                    cm.Key(y => y.PropertyRef(bt => bt.ParentBusinessTypeId));
                    cm.Inverse(true);
                    cm.OrderBy(bt => bt.BusinessTypeName);
                    cm.Lazy(CollectionLazy.NoLazy);
                },
            m => m.OneToMany());
    }
}

The problem is that this causes NHibernate to generate a column called businesstype_key, ignoring the already-configured ParentBusinessTypeId. Is there any way to make NHibernate use a lambda to specify the relation, rather than a string?

Answer 1

I never need to navigate from children to parents, only from parents
to children, so I hadn’t thought it necessary

then remove public virtual Guid? ParentBusinessTypeId { get; set; } completly. NH will then only create “businesstype_key” (convention) and no “ParentBusinessTypeId”. if you want to change that then you have to specify your prefered columnname with cm.Key(y => y.Column("yourpreferredColumnName"));