Hello Stefano,

EntitySet<> could be created only with Entity/IEntity derived types. So your Generic<> should be an entity.

DataObjects.Net supports generic entities in two possible scenarios:

1) It could use any generic type if you register all required generic instances in DomainConfiguration explicitly:

var configuration = DomainConfiguration.Load("MyDomain");
configuration.Types.Register(typeof (MyGeneric<MyOtherType>));
configuration.Types.Register(typeof (MyGeneric<MyAnotherType>));

In this sample you could use MyGeneric<MyOtherType> and MyGeneric<MyAnotherType> as a regular Entity. However no other MyGeneric<> instantiations will work.

2) If generic type satisfies some conditions DataObjects.Net applies so called automatic generic instantiation. To have it working all your generic parameters should have a type constraint: either Entity/IEntity or their derived types/interfaces. Let me show you some example:

// This interface marks all entities suitable for audit
public interface IAuditable : IEntity
{
}

// This is audit record.
// Any auditable entities would be automatically substituted as TEntity
// and corresponding generic instance would be available in domain.
[HierarchyRoot]
public class AuditRecord<TEntity> : Entity 
  where TEntity : Entity, IAuditable
{
  [Key, Field]
  public long Id { get; private set; }

  [Field]
  public TEntity Target { get; private set; }
}

// This entity does not match AuditRecord<> constraints.
// AuditRecord<EntityA> would not be created.
[HierarchyRoot]
public class EntityA : Entity 
{
  [Key, Field]
  public long Id { get; private set; }
}

// This entity matches AuditRecord<> constraints.
// AuditRecord<EntityB> would be created.
[HierarchyRoot]
public class EntityB : Entity, IAuditable
{
  [Key, Field]
  public long Id { get; private set; }
}

// This entity also matches AuditRecord<> constraints,
// however AuditRecord<EntityC> would not be created because
// DataObjects.Net instantiates generics only for the most base type
// in the hierarchy that matches constraint. In our sample it is EntityB.
[HierarchyRoot]
public class EntityC : EntityB 
{
  [Key, Field]
  public long Id { get; private set; }
}