[nhusers] Joined sub-class mapping where some sub classes have an abstract base class

[Andre]

Hello, 


I have a class hierarchy that conceptually looks similar to this:

<https://lh4.googleusercontent.com/-w3hKntlRKnY/UUlxrFoGCwI/AAAAAAAAAGA/J3kwGDGDT-k/s1600/original.jpg>



That is, there's an abstract base class (Relation) and a couple of derived 
classes. In practice, Customer and Supplier share a lot of code, so I 
refactored the commonoalities into an abstract class BusinessContact. Now 
the actual class hierarchy looks like this:


<https://lh4.googleusercontent.com/-gK8StoiTOLw/UUlxwXsdouI/AAAAAAAAAGI/puqW6tyODqY/s1600/augmented.jpg>

        
Or in code:

    public abstract class Relation
    {
        public virtual int Id { get; set; }
    }

    public class ContactPerson : Relation
    {
        public virtual string PhoneNumber { get; set; }
    }

    public abstract class BusinessContact : Relation
    {
        public virtual string Name { get; set; }
    }

    public class Customer : BusinessContact
    {
        public virtual string CustomerNumber { get; set; } 
    }

    public class Supplier : BusinessContact
    {
        public virtual string SupplierNumber { get; set; }
    }

I'd like to map this hierarchy to four tables (Relation, ContactPerson, 
Customer and Supplier) using joined-subclasses in NHibernate, using 
mapping-by-code (ModelMapper). My mapping looks like this:

    var mapper = new ModelMapper();

    mapper.Class<Relation>(map =>
    {
        map.Id(x => x.Id, id => id.Generator(Generators.Native));
    });

    mapper.JoinedSubclass<ContactPerson>(map =>
    {
        map.Key(key => key.Column("Id"));
        map.Property(x => x.PhoneNumber);
    });

    mapper.JoinedSubclass<Customer>(map =>
    {
        map.Key(key => key.Column("Id"));
        map.Property(x => x.Name);
        map.Property(x => x.CustomerNumber);
    });

    mapper.JoinedSubclass<Supplier>(map =>
    {
        map.Key(key => key.Column("Id"));
        map.Property(x => x.Name);
        map.Property(x => x.SupplierNumber);
    });



However, as soon as I try to add the mapping to the Configuration I get an 
exception:

    NHibernate.MappingException: Cannot extend unmapped class: 
BusinessContact

I basically understand why this happens. The generated mapping looks like 
this:

    <?xml version="1.0" encoding="utf-8"?>
    <hibernate-mapping 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"; 
xmlns:xsd="http://www.w3.org/2001/XMLSchema"; 
namespace="JoinedSubClassMapping" assembly="JoinedSubClassMapping" 
xmlns="urn:nhib    ernate-mapping-2.2">
      <class name="Relation" abstract="true">
        <id name="Id" type="Int32">
          <generator class="native" />
        </id>
      </class>
      <joined-subclass name="ContactPerson" extends="Relation">
        <key column="Id" />
        <property name="PhoneNumber" />
      </joined-subclass>
      <joined-subclass name="Customer" extends="BusinessContact">
        <key column="Id" />
        <property name="CustomerNumber" />
      </joined-subclass>
      <joined-subclass name="Supplier" extends="BusinessContact">
        <key column="Id" />
        <property name="SupplierNumber" />
      </joined-subclass>
    </hibernate-mapping>

Customer and Supplier define BusinessContact in their extends attribute, as 
if BusinessContact was a "normal" entity in the model. As there's no 
mapping for BusinessContact, this fails, or course. Note that the "Name" 
property (defined in BusinessContact does not appear in the mapping either.

What I *want *the mapping to look like is this:

    <?xml version="1.0" encoding="utf-8" ?>
    <hibernate-mapping 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"; 
xmlns:xsd="http://www.w3.org/2001/XMLSchema"; 
namespace="JoinedSubClassMapping" assembly="JoinedSubClassMapping" 
xmlns="urn:nhibernate-mapping-2.2">
      <class name="Relation" abstract="true">
        <id name="Id" type="Int32">
          <generator class="native" />
        </id>
      </class>
      <joined-subclass name="ContactPerson" extends="Relation">
        <key column="Id" />
        <property name="PhoneNumber" />
      </joined-subclass>
      <joined-subclass name="Customer" extends="Relation">
        <key column="Id" />
        <property name="CustomerNumber" />
        <property name="Name" />
      </joined-subclass>
      <joined-subclass name="Supplier" extends="Relation">
        <key column="Id" />
        <property name="SupplierNumber" />
        <property name="Name" />
      </joined-subclass>
    </hibernate-mapping>

That is, make Supplier and Customer extend Relation and include all the 
mapped properties of the (otherwise unmapped) BusinessContact class.

How can I achieve this?

Thanks a lot for your time,
Andre

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