Mapping a struct as Id in nhibernate - nhibernate

Question

I have the following struct and class:
public struct DepartmentId{
public int Value {get; set;}
}
public class Department{
public virtual DepartmentId Id{get;set;}
public virtual string Name {get; set;}
}
I created a mapping file for Department as follows:
public class DepartmentMapping : ClassMapping<Department>{
public DepartmentMapping{
Table("Department");
Id(dept => dept.Id, mapper => {
mapper.Column("Id");
mapper.Type(new DepartmentIdType());
});
Property(dept => dept.Name, mapper => mapper.Column("Name"));
}
}
where DepartmentIdType implements IIdentifierType:
class DepartmentIdType : PrimitiveType, IIdentifierType
{
public DepartmentIdType() : base(SqlTypeFactory.Int32)
{
}
public override object DeepCopy(object val, EntityMode entityMode, ISessionFactoryImplementor factory)
{
return val;
}
public override object Replace(object original, object current, ISessionImplementor session, object owner, IDictionary copiedAlready)
{
return original;
}
public override Type ReturnedClass
{
get { return typeof(DepartmentId); }
}
public object StringToObject(string xml)
{
return new DepartmentId {Value = int.Parse(xml)};
}
public override string Name
{
get { return typeof(DepartmentId).Name; }
}
public override void Set(IDbCommand cmd, object value, int index)
{
var id = (DepartmentId) value;
((IDataParameter) cmd.Parameters[index]).Value = id.Value;
}
public override object Get(IDataReader rs, int index)
{
int value = rs.GetInt32(index);
return new DepartmentId {Value = value};
}
public override object Get(IDataReader rs, string name)
{
return Get(rs, rs.GetOrdinal(name));
}
public override string ToString(object val)
{
if (val == null) return "";
return val.ToString();
}
public override object FromStringValue(string xml)
{
return new DepartmentId {Value = Int32.Parse(xml)};
}
public override object DefaultValue
{
get { return new DepartmentId {Value = 0}; }
}
public override string ObjectToSQLString(object value, NHibernate.Dialect.Dialect dialect)
{
return value.ToString();
}
public override Type PrimitiveClass
{
get { return typeof(DepartmentId); }
}
}
However, at the time of creating the HbmMapping, I get the following error:
Could not compile the mapping document: mapping_by_code
NHibernate.MappingException: Could not compile the mapping document:
mapping_by_code ---> NHibernate.MappingException:
Could not determine type for: Demo.Models.DepartmentId, Demo.Models,
for columns: NHibernate.Mapping.Column(Id)
at NHibernate.Mapping.SimpleValue.get_Type()
at NHibernate.Cfg.XmlHbmBinding.ClassIdBinder.CreateIdentifierProperty(HbmId idSchema, PersistentClass rootClass, SimpleValue id)
at NHibernate.Cfg.XmlHbmBinding.ClassIdBinder.BindId(HbmId idSchema, PersistentClass rootClass, Table table)
at NHibernate.Cfg.XmlHbmBinding.RootClassBinder.Bind(HbmClass classSchema, IDictionary`2 inheritedMetas)
at NHibernate.Cfg.XmlHbmBinding.MappingRootBinder.AddRootClasses(HbmClass rootClass, IDictionary`2 inheritedMetas)
at NHibernate.Cfg.XmlHbmBinding.MappingRootBinder.AddEntitiesMappings(HbmMapping mappingSchema, IDictionary`2 inheritedMetas)
at NHibernate.Cfg.XmlHbmBinding.MappingRootBinder.Bind(HbmMapping mappingSchema)
at NHibernate.Cfg.Configuration.AddDeserializedMapping(HbmMapping mappingDocument, String documentFileName)
How do I fix this issue (without changing DepartmentId from struct to class)?
Thanks in advance for your help.

Answer 1

I suggest using class instead of struct and ComponentAsId instead of Id method for this case. If you don't use id generator it is a straightforward approach without any hacking.
public class DepartmentMapping : ClassMapping<Department> {
public DepartmentMapping{
Table("Department");
ComponentAsId(dept => dept.Id);
Property(dept => dept.Name, mapper => mapper.Column("Name"));
}}
public class DepartmentIdMapping : ComponentMapping<DepartmentId> {
public DepartmentIdMapping{
Property(x=> x.Value, mapper => mapper.Column("Id"));
}}
I tried your approach when investigating this strong typed ids together with id generation but I finally decided to implement custom Hi/Lo generator and use NHibernate assigned ids.

Answer 2

I'm just going to put this here for a reference.
In XML mapping, I did this through mapping as a composite id:
<class name"Department" ... >
<composite-id name="Id" access="property"
class="DepartmentId">
<key-property name="Value"
column="Id"
access="property"
type="System.Int32"/>
</composite-id>
... other stuff
</class>