Better integration with modern .NET practices

[ah1508]

EF Core is catching up and even if Nhibernate still have unique and more advanced features, the lack of

• built-in integration with modern .NET
• mapping by code documentation (already mentionned in another issue). Until now the most reliable and comprehensive documentation of mapping by code http://notherdev.blogspot.com/2012/02/nhibernates-mapping-by-code-summary.html

does not help onboarding for new comers.

Suggestions:

The ConventionalModelMapper could register ClassMapping by introspection, like for hbm.xml files.

It would avoid this kind of boilerplate:

public class MyMapper : ConventionModelMapper
{
    public MyMapper()
    {
        GetType().Assembly.GetTypes().Where(t =>
            t.BaseType != null &&
            t.BaseType.IsGenericType &&
            t.BaseType.GetGenericTypeDefinition() == typeof(ClassMapping<>)
        ).ToList().ForEach(AddMapping);
}

The integration with modern dotnet standards (ILogger, IConfiguration) could be built-in. The default setup still relies on hibernate.cfg.xml while IConfiguration abstraction has beeen the standard for many years now.

Coupling with ILogger requires an extension (NHibernate.Extensions.Logging) while it could also be built-in.

To sum up, I'd love to see that:

ISessionFactory sessionFactory = ISessionFactory.Create(configuration, loggerFactory, "myassembly");

where configuration is an instance of IConfiguration with a NHibernate section.

Implémentation proposal of this method:

    public static ISessionFactory Create(IConfiguration configuration, ILoggerFactory loggerFactory, string assembly, Action<NHibernate.Cfg.Configuration>? customizer = null)
    {
        return Create(configuration, loggerFactory, new string[] { assembly }, customizer);
    }

    public static ISessionFactory Create(IConfiguration configuration, ILoggerFactory loggerFactory, string[] assemblies, Action<NHibernate.Cfg.Configuration>? customizer = null)
    {
        var logger = NHibernateLogger.For(typeof(ISessionFactory));
        logger.Info("Configure logging: NHibernate will use Microsoft.Extensions.Logging");
        NHibernateLogger.SetLoggersFactory(new MicrosoftLoggerFactory(loggerFactory)); // equivalent : loggerFactory.UseAsNHibernateLoggerProvider();
        
        logger.Info("Get properties from NHibernate configuration section");
        IDictionary<string, string> properties = configuration.GetSection("NHibernate")
           .GetChildren()
           .Where(x => x.Value != null)
           .ToDictionary(x => x.Key, x => x.Value!);

        if (properties.TryGetValue(NHibernate.Cfg.Environment.ConnectionStringName, out var connStringName) && !string.IsNullOrWhiteSpace(connStringName))
        {
            logger.Info("Property {0} references connection string {1}", NHibernate.Cfg.Environment.ConnectionStringName, connStringName);
            var connectionString = configuration.GetConnectionString(connStringName) ?? throw new Exception(connStringName + " does not exists");
            logger.Info("Add property {0}", NHibernate.Cfg.Environment.ConnectionString);
            properties[NHibernate.Cfg.Environment.ConnectionString] = connectionString;
            properties.Remove(NHibernate.Cfg.Environment.ConnectionStringName);
        }
        var cfg = new NHibernate.Cfg.Configuration { Properties = properties };

        foreach (var assembly in assemblies.Select(Assembly.Load))
        {
            logger.Info("Register {0}", assembly.GetName());
            cfg.AddAssembly(assembly); // for hbm.xml files

            assembly.GetTypes()
                .Where(t => typeof(ModelMapper).IsAssignableFrom(t))
                .Select(t => Activator.CreateInstance(t))
                .OfType<ModelMapper>()
                .ToList()
                .ForEach(mapper =>
                {
                    logger.Info("Register {0} as {0}", mapper.GetType().Name, nameof(ModelMapper));
                    cfg.AddMapping(mapper.CompileMappingForAllExplicitlyAddedEntities());
                });
        }
        if (customizer != null)
        {
            logger.Info("Apply {0} on configuration", nameof(customizer));
            customizer(cfg);
        }
        logger.Info("Create SessionFactory");
        var sessionFactory = cfg.BuildSessionFactory();
        logger.Info("SessionFactory ready");
        return sessionFactory;
    }

I also think that a "transactional session context" should be added (see #1907 (comment)). TransactionScope is a bit forgotten but remains a neutral way to surround a unit of work. It does not dispose asynchronously but all other implementations of ICurrentSessionContext have also their drawbacks.

My point: it's a pity if NHibernate, which is not as popular as EFCore despite several more advanced features, gives the feeling to be behind modern dotnet because of a few details.

[hazzik]

Thanks for your input @ah1508, however, that is more a discussion than an issue as this is not really actionable.

[fredericDelaporte]

Theses features should be considered for 6.0 I think.

[knuxbbs]

I agree with all the points bring by the OP. Especially the lack of documentation for mapping by code.

How could we help with this, specifically?

[fredericDelaporte]

Documentation can be contributed in the core repository in docbook format. It is in the doc sub-folder. The end result will be published on next minor as "The NHibernate Reference" here.

[ah1508]

How about contacting the author of http://notherdev.blogspot.com/2012/02/nhibernates-mapping-by-code-summary.html ? Maybe some parts must be rephrased, but it's better than writing everything from scratch. For the time being it is the most accurate source of documentation.