Fluent NHibernate Generated Audits

Question

I need some help setting up my Fluent NHibernate POCO class structure. I'm trying to simply have a way to make an object auditable. On Create, I want my created and modified datetimes to be set and on update, I want my modified to be updated. I've been following some examples, but I have hit a road block. This is my current setup:

IAuditable.cs

namespace ZeroBase.Domain.Entities
{
public interface IAuditable
{
    DateTime Created
    {
        get;
    }

    DateTime Modified
    {
        get;
    }

    string CreatedPropertyName
    {
        get;
    }

    string ModifiedPropertyName
    {
        get;
    }

    void SetCreationDate(DateTime created);
    void SetModifiedDate(DateTime modified);
}
}

AuditableEntity.cs

namespace ZeroBase.Domain.Entities
{
public class AuditableEntity<T> : IAuditable
{
    public DateTime Created { get; private set; }
    public DateTime Modified { get; private set; }

    void IAuditable.SetCreationDate(DateTime created)
    {
        this.Created = created;
    }

    void IAuditable.SetModifiedDate(DateTime modified)
    {
        this.Modified = modified;
    }

    string IAuditable.CreatedPropertyName
    {
        get
        {
            string createdPropName = "Created";

        #if DEBUG
            CheckIfPropertyExists(createdPropName);
        #endif

            return createdPropName;
        }
    }

    string IAuditable.ModifiedPropertyName
    {
        get
        {
            string modifiedPropName = "Modified";

        #if DEBUG
            CheckIfPropertyExists(modifiedPropName);
        #endif

            return modifiedPropName;
        }
    }

    private void CheckIfPropertyExists(string propertyName)
    {
        PropertyInfo pi = this.GetType().GetProperty(propertyName);
        Debug.Assert(pi != null, String.Format("There exists no property {0}", propertyName));
    }
}
}

User.cs

namespace ZeroBase.Domain.Entities
{
public class User : AuditableEntity<User>
{
    public virtual Guid Id { get; set; }
    public virtual string Username { get; set; }
    public virtual string Password { get; set; }
    public virtual string FirstName { get; set; }
    public virtual string LastName { get; set; }
    public virtual string EmailAddress { get; set; }
    public virtual IEnumerable<Comment> Comments { get; set; }
}
}

AuditInterceptor.cs

namespace ZeroBase.Infrastructure.Data
{
public class AuditInterceptor : EmptyInterceptor
{
    public override bool OnFlushDirty(object entity, object id, object[] currentState, object[] previousState,
        string[] propertyNames, NHibernate.Type.IType[] types)
    {
        IAuditable auditableObject = entity as IAuditable;

        if (auditableObject != null)
        {
            for (int i = 0; i < propertyNames.Length; i++)
            {
                if (propertyNames[i] == auditableObject.ModifiedPropertyName)
                {
                    currentState[i] = DateTime.Now;
                }
            }
            return true;
        }

        return false;
    }

    public override bool OnSave(object entity, object id, object[] state, string[] propertyNames, NHibernate.Type.IType[] types)
    {
        IAuditable auditableObject = entity as IAuditable;

        if (auditableObject != null)
        {
            DateTime currentDate = DateTime.Now;

            for (int i = 0; i < propertyNames.Length; i++)
            {
                if (propertyNames[i] == auditableObject.CreatedPropertyName)
                {
                    state[i] = currentDate;
                }
                if (propertyNames[i] == auditableObject.ModifiedPropertyName)
                {
                    state[i] = currentDate;
                }
            }

            System.Diagnostics.Debug.WriteLine("interceptor: created: " + auditableObject.Created);
            System.Diagnostics.Debug.WriteLine("interceptor: modified: " + auditableObject.Modified);

            return true;
        }

        return false;
    }
}
}

AuditMap.cs

namespace ZeroBase.Infrastructure.Data
{
public class AuditMap<T>: ClassMap<T> where T : AuditableEntity<T>
{
    public AuditMap()
    {
        Map(p => p.Created);
        Map(p => p.Modified);
    }
}
}

UserMap.cs

namespace ZeroBase.Infrastructure.Data
{
public class UserMap : AuditMap<User>
{
    public UserMap()
    {
        Id(x => x.Id)
            .Column("Id")
            .GeneratedBy.Guid();
        Map(x => x.Username);
        Map(x => x.Password);
        Map(x => x.FirstName);
        Map(x => x.LastName);
        Map(x => x.EmailAddress);
        HasMany(x => x.Comments);
        Table("Users");
    }
}
}

SessionHelper.cs

_sessionFactory = Fluently.Configure()

            // Set up database connection
            .Database(MsSqlConfiguration.MsSql2005
                .ConnectionString(x => x.Is(_connectionString))
                //.ShowSql()
            )

            // Use class mappings
            .Mappings(m => m.FluentMappings
                .AddFromAssemblyOf<UserMap>())

            .ExposeConfiguration(c => c.SetInterceptor(new AuditInterceptor()))

            .BuildSessionFactory();

When I try to run this, I get this runtime error: The following types may not be used as proxies: ZeroBase.Domain.Entities.User: method get_Created should be 'public/protected virtual' or 'protected internal virtual' ZeroBase.Domain.Entities.User: method get_Modified should be 'public/protected virtual' or 'protected internal virtual'"}

What is this trying to tell me?

Does this have anything to do with Fluent NHibernate?

I'm a little confused and would love some help!

Answer 1

Created and Modified properties in your AuditableEntity<T> class need to be virtual. This is a requirement of NHibernate, if you are using lazy loading (on by default).

Also, there are some questions about it here on SO.