How do I get table-per-inheritance-hierarchy to work with Fluent NHibernate AutoMapping and integer discriminators?

Question

I've tried searching for information on this all over the place, but no one seems to quite cover this issue. I've reduced it to the following example.

This is my database :

create table ThingTypes
(
    Id int,
    Name varchar(50) not null

    constraint PK_ThingTypes primary key (Id)
)
go

insert into ThingTypes(Id, Name) Values(1, 'ThingTypeOne')
insert into ThingTypes(Id, Name) Values(2, 'ThingTypeTwo')

create table Things
(
    Id int identity,
    Name varchar(50) not null,
    ThingTypeId int not null

    constraint PK_Things primary key (Id),
    constraint FK_Things_ThingTypes foreign key (ThingTypeId) references ThingTypes(Id)
)
go

This is my model :

public abstract class Thing
{
    public virtual int Id { get; set; }
    public virtual string Name { get; set; }
}
public class ThingTypeOne : Thing { }
public class ThingTypeTwo : Thing { }

These are my mappings :

public class ThingOverride : IAutoMappingOverride<Thing>
{
    public void Override(AutoMapping<Thing> mapping)
    {
        mapping.DiscriminateSubClassesOnColumn("ThingTypeId", 0);
    }
}

public class ThingTypeOneMap : SubclassMap<ThingTypeOne>
{
    public ThingTypeOneMap()
    {
        DiscriminatorValue(1);
    }
}

public class ThingTypeTwoMap : SubclassMap<ThingTypeTwo>
{
    public ThingTypeTwoMap()
    {
        DiscriminatorValue(2);
    }
}

This is my ISessionFactory builder :

public static ISessionFactory GetFactory(string connectionString)
{
    var configuration = new Configuration().AddProperties(new Dictionary<string, string>
        {
            {Environment.ConnectionDriver, typeof (SqlClientDriver).FullName},
            {Environment.Dialect, typeof (MsSql2008Dialect).FullName},
            {Environment.ConnectionProvider, typeof (DriverConnectionProvider).FullName},
            {Environment.ConnectionString, connectionString},
            {Environment.ShowSql, "true"},
            {Environment.BatchSize, "100"},
            {Environment.Isolation, "ReadCommitted"}
        });

    return Fluently.Configure(configuration)
                    .Mappings(m =>
                        {
                            m.FluentMappings.AddFromAssemblyOf<ThingTypeOneMap>();
                            m.AutoMappings.Add(AutoMap.AssemblyOf<Thing>(new DefaultAutomappingConfiguration())
                                                        .UseOverridesFromAssemblyOf<ThingOverride>()
                                );
                        })
                    .BuildSessionFactory();
}

And this is my failing test :

var sessionFactory = SessionFactoryBuilder.GetFactory(@"Data Source=localhost;Initial Catalog=ThingDatabase;Trusted_Connection=True;");
using (var session = sessionFactory.OpenSession())
{
    session.BeginTransaction();
    session.SaveOrUpdate(new ThingTypeOne
        {
            Name = "New Thing Type One"
        });
    session.Transaction.Commit();
}

It fails because it tries to insert into table "ThingTypeOne", which obviously doesn't exist. What do I need to do to get Fluent NHibernate to actually pay attention to the DiscriminateSubClassesOnColumn property that I've set?

I can get this working if I don't use AutoMapping, i.e. exclude all the table-per-inheritance-hierarchy classes from the auto mapping (adding && !typeof(Thing).IsAssignableFrom(type) to the ShouldMap method of my DefaultAutomappingConfiguration extension) but my base class has a lot of properties and I *really* want to use AutoMapping... — adhocgeek, Nov 01 '13 at 17:05
That doesn't work because then you end up with the exception "Duplicate class/entity mapping ThingTypeOne". — adhocgeek, Nov 04 '13 at 09:05

score 2 · Accepted Answer · answered Nov 04 '13 at 09:35

instead of subclassmaps for each subclass add a convention

class DiscriminatorValueConvention : ISubclassConvention
{
    public void Apply(ISubclassInstance instance)
    {
        if (instance.Type == typeof(ThingTypeOne))
        {
            instance.DiscriminatorValue(1);
        }
        else if (instance.Type == typeof(ThingTypeTwo))
        {
            instance.DiscriminatorValue(2);
        }
    }
}

How do I get table-per-inheritance-hierarchy to work with Fluent NHibernate AutoMapping and integer discriminators?

1 Answers1