Question

I’m converting a previous project from using normal NHibernate hbm.xml mappings to Fluent NHibernate. Currently, I’m stuck on what should be one of the last steps to getting this working. I’ve added a derived class for DefaultAutomappingConfiguration to modify my ID naming convention. The string “Id” is appended to the class name:

    public override bool IsId(FluentNHibernate.Member member)
    {
        return member.Name == member.DeclaringType.Name + "Id";
    }

This should make “Agency” have an ID in a field named “AgencyId”. Instead, I’m getting this error:

The entity 'ClassMap`1' doesn't have an Id mapped. Use the Id method to map your identity property. For example: Id(x => x.Id).
{Name = "ClassMap`1" FullName = "FluentNHibernate.Mapping.ClassMap`1[[BackendDb.Model.Agency, BackendDb, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]"}

I made a breakpoint on the IsId function to see what’s going on:

{Property: Cache}
{Name = "ClassMap`1" FullName = "FluentNHibernate.Mapping.ClassMap`1[[BackendDb.Model.Agency, BackendDb, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]"}

What is this? The object is not something I’ve created. Every other object passes through this function fine, and the ones I actually wanted to map are returning the proper value.

My Session factory looks something like this:

var cfg = new MapConfig();
return Fluently.Configure()
.Database(MsSqlConfiguration.MsSql2008
.ConnectionString(m => m.Server(@".\SqlExpress")
    .Database("{some dbname}")
    .TrustedConnection()))
.Mappings(m =>
    m.AutoMappings
        .Add(AutoMap.AssemblyOf<Agency>(cfg))
)
.BuildSessionFactory();

Annoyingly, it seems that this somehow caused the three tables I was testing Fluent NHibernate on in my dev database to be emptied. What the hell?

Answer 1

The sessionfactory is trying to automap all classes in the assembly that contains your Agency class based on this directive: Add(AutoMap.AssemblyOf<Agency>(cfg)). Since you have an AgencyMap in the assembly andClassMap<> does not have an Id property, FNH is throwing an error.

If you want to use ClassMap<> configurations, instead of (or in addition to) declaring an automapping configuration, declare a fluent mapping:

m.FluentMappings.AddFromAssemblyOf<Agency>();

If you don’t need AutoMappings, remove the `.AutoMappings.Add’ directive.

However, if you want to use AutoMappings, you need to tell FNH what classes you want to map. To handle this, I usually define a marker interface:

public abstract class Entity : IPersistable
{
    public virtual int Id { get; set; }
}

public interface IPersistable
{
}

Then, in the class that I derive from DefaultAutomappingConfiguration, I tell FNH to only map the classes that have that interface (you can limit the mapped classes however you see fit):

public class EntityAutoMappingConfiguration : DefaultAutomappingConfiguration
{
    public override bool ShouldMap(Type type)
    {
        return type.GetInterfaces().Contains(typeof (IPersistable));
    }

}

To handle the primary key mapping, I create a convention class:

public class PrimaryKeyNamePlusId : IIdConvention 
{
    public void Apply(IIdentityInstance instance)
    {
        instance.Column(instance.EntityType.Name+"Id");
    }
}

Finally, I configure my SessionFactory to use the configuration/convention classes:

 m.AutoMappings.AssemblyOf<Entity>(new EntityAutoMappingConfiguration())
            .IgnoreBase<Entity>()
            .UseOverridesFromAssemblyOf<Entity>()
            .Conventions.AddFromAssemblyOf<Entity>();