Question

I am reading data from an external organisation using Oracle.DataAccess through the Oracle10g provider. One of the tables has a composite id made up of these fields.

course:
  institutioncode: "X11"
  coursecode:      "N100"
  campuscode:      "A"
  entryyear:       2011
  entrymonth:      10

The problem is that the campus code is allowed to be null by the external provider instead of empty. This leads to nHibernate returning collections that contain null references instead of course entities.

Other domain objects will use these fields to refer to this course entity as well, so this is actually used as a key and I can’t easily remap to use a surrogate key.

From the source in tag 3.1.0GA, the check that is causing this behavior can be found in Nhibernate.Type.ComponentType.Hydrate(IDataReader rs, string[] names, ISessionImplementor session, object owner). This is always refusing the possibility that a key-property could be null. Could this change to make nullability an option on key-property and key-reference properties?

Failing that, how would you recommend reading this data directly with nHibernate?

Answer 1

ok my first comment didnt worked out on References (ManyToOne). So here my alternative solution: a usertype to work around the check.

class CourseMap : ClassMap<Course>
{
    public CourseMap()
    {
        CompositeId()
            .KeyProperty(c => c.InstitutionCode)
            .KeyProperty(c => c.CourseCode)
            .KeyProperty(c => c.CampusCode, key => key.Type(typeof(MyUserType)))
            .KeyProperty(c => c.EntryYear)
            .KeyProperty(c => c.EntryMonth);
    }
}

class MyUserType : IUserType
{
    public object Assemble(object cached, object owner)
    {
        return DeepCopy(cached);
    }

    public object DeepCopy(object value)
    {
        return value;
    }

    public object Disassemble(object value)
    {
        return DeepCopy(value);
    }

    public new bool Equals(object x, object y)
    {
        return object.Equals(x, y);
    }

    public int GetHashCode(object x)
    {
        return (x == null) ? 0 : x.GetHashCode();
    }

    public bool IsMutable
    {
        get { return false; }
    }

    public object NullSafeGet(IDataReader rs, string[] names, object owner)
    {
        var value = NHibernateUtil.String.NullSafeGet(rs, names[0]);
        return (value == null) ? string.Empty : value;
    }

    public void NullSafeSet(IDbCommand cmd, object value, int index)
    {
        string d = string.IsNullOrEmpty((string)value) ? null : (string)value;
        NHibernateUtil.String.NullSafeSet(cmd, d, index);
    }

    public object Replace(object original, object target, object owner)
    {
        return DeepCopy(original);
    }

    public Type ReturnedType
    {
        get { return typeof(string); }
    }

    public SqlType[] SqlTypes
    {
        get { return new[] { SqlTypeFactory.GetString(100) }; }
    }
}



class SomeEntityMap : ClassMap<SomeEntity>
{
    public EntityMap()
    {
        Id(e => e.Id).GeneratedBy.Assigned();

        References(e => e.Course)
            .Columns("InstitutionCode", "CourseCode", "CampusCode", "EntryYear", "EntryMonth")
            .Fetch.Join();  // important because we can't rely on values, NULL is invalid value
    }
}