How to reference parent entity in the same table with fluent nhibernate auto mappings?

Question

I am trying to use FluentNHibernate AutoMappings to create an entity with reference to its parent. I was able to do this with help of ClassMap<>, but now I want to move everything to AutoMappings. I have a table with the following schema:

CREATE TABLE [dbo].[Job]
(
   [Id] INT NOT NULL IDENTITY(1,1), 
   [ParentId] INT NULL, 
   PRIMARY KEY ([Id]), 
   CONSTRAINT [FK_Job_Parent] FOREIGN KEY ([ParentId]) REFERENCES [Job]([Id]) 
)

And the following C# code:

using FluentNHibernate;
using FluentNHibernate.Automapping;
using FluentNHibernate.Cfg;
using FluentNHibernate.Cfg.Db;
using FluentNHibernate.Conventions;
using FluentNHibernate.Conventions.Instances;
using System;
using System.Configuration;

namespace NHibernateTest
{
    public class Program
    {
        private static void Main(string[] args)
        {
            var sessionFactory = Fluently.Configure()
              .Database(MsSqlConfiguration.MsSql2008.ConnectionString(ConfigurationManager.ConnectionStrings["Default"].ConnectionString))
              .Mappings(m =>
              {
                  m.AutoMappings.Add(
                      AutoMap.AssemblyOf<Program>(new MappingConfig()).Conventions.Setup(conv =>
                  {
                      conv.Add<DefaultReferenceConvention>();
                      conv.Add<DefaultHasManyConvention>();
                      conv.Add<SimpleForeignKeyConvention>();
                  }));
              })
              .BuildSessionFactory();

            using (var session = sessionFactory.OpenSession())
            {
                using (var tran = session.BeginTransaction())
                {
                   var jobs = session
                        .QueryOver<Job>()
                        .List<Job>();

                    tran.Commit();
                }
            }
        }
    }

    public class Job
    {
        public virtual int Id { get; set; }

        public virtual Job Parent { get; set; }
    }

    public class MappingConfig : DefaultAutomappingConfiguration
    {
        public override bool ShouldMap(Type type)
        {
            return type == typeof(Job);
        }
    }

    public class SimpleForeignKeyConvention : ForeignKeyConvention
    {
        protected override string GetKeyName(Member property, Type type)
        {
            if (property == null)
            {
                return type.Name + "Id";
            }

           return property.Name + "Id";
        }
    }

    public class DefaultHasManyConvention : IHasManyConvention
    {
        public void Apply(IOneToManyCollectionInstance instance)
        {
            instance.Key.Column(string.Format("{0}{1}", instance.EntityType.Name, "Id"));
            instance.LazyLoad();
        }
    }

    public class DefaultReferenceConvention : IReferenceConvention
    {
        public void Apply(IManyToOneInstance instance)
        {
            var col = string.Format("{0}Id", instance.Class.Name);
            instance.Column(col);
            instance.LazyLoad();
        }
    }
}

I am getting:

An invalid or incomplete configuration was used while creating a SessionFactory. Check PotentialReasons collection, and InnerException for more detail.

Foreign key (FK7D5D63A6AE42E0BA:Job [JobId, ParentId])) must have same number of columns as the referenced primary key (Job [Id])

Is there a way to do this using auto mappings only?

Answer 1

Your DefaultReferenceConvention appears to conflict with your SimpleForeignKeyConvention . One of them uses the property name as the basis for the column name, the other uses the property type . It looks like for some reason Fluent NH is using both of these, and thinks you have a composite key.

Remove DefaultReferenceConvention and see if that fixes it. It's unnecessary anyway because Fluent NH's default foreign key column naming is already {Class.Name}Id .

Fluent NH conventions are excellent for painting your mappings with broad brush strokes, but they are not the right tool for changing the column name of a single property. In that case, you should define an IAutoMappingOverride<T> instead.