Fluent NHibernate ignore property inside the ClassMap, using FluentMappings

Question

I am using NHibernate 3.1 and Fluent NHibernate as ORM in my project. I need to have a property of a POCO ignored by Fluent NHibernate. At first, my post might look as exact duplicate of this question, but it is not.

My complications come first from the fact that the POCOs are defined in a different assembly than the mapping and I am using fluent mappings for my POCOs. I have additional requirement not to write ingore-property code where the session factory configuration takes place (this happens at a centralized place outside the modules), but as part of the module that defines the mappings. Ideally, I believe the right place would be the concrete ClassMap implementation, since it knows exactly how to describe a POCO to the ORM.

However, I am stuck on this mainly because this is my first impact with NHibernate and its fluent API. Up to now I am having very good impression of its capabilities and extensibility, and I hope there is a way to achieve my requirement in a way that the mapping related code is encapsulated in its corresponding module.

Here is my configuration, from a centralized place:

List<Assembly> assemblies = GetModules().Select(x => x.GetType().Assembly).ToList();

ISessionFactory nhibernateSessionFactory = Fluently
    .Configure()
    .Mappings(m => assemblies.ForEach(asm => m.FluentMappings.AddFromAssembly(asm)))
    .Database(
        MsSqlConfiguration.MsSql2005
            .ShowSql()
            .ConnectionString(DatabaseConfig.Instance.ConnectionString))
    .ExposeConfiguration(c => new SchemaUpdate(c).Execute(true, true))
    .BuildSessionFactory();

I use standard class mappings that inherit from ClassMap:

public class User
{
    public virtual int ID { get; set; }
    public virtual String Username { get; set; }
    public virtual String Password { get; set; }
    public virtual DateTime DateCreated { get; set; }
    public virtual DateTime DateModified { get; set; }

    // Must ignore
    public string ComputedProperty  { get { ... } }
}

public class UserMap : ClassMap<User>
{
    public UserMap()
    {
        Table("User");
        Id(x => x.ID).GeneratedBy.Identity();
        Map(m => m.Username).Not.Nullable().Length(255).UniqueKey("User_Username_Unique_Key");
        Map(m => m.Password).Not.Nullable().Length(255);
        Map(m => m.DateCreated).Not.Nullable();
        Map(m => m.DateModified).Not.Nullable();
    }
}

Answer 1

I think you are right that the ClassMap is the best place to ignore this property.

Example:

.Override<Shelf>(map =>  
{  
  map.IgnoreProperty(x => x.YourProperty);
});

Documentation: https://github.com/jagregory/fluent-nhibernate/wiki/Auto-mapping#ignoring-properties

As far as getting the mappings from another assembly, it should be as easy as something like this (depending on your current configuration):

.Mappings(m =>
              {
                  m.FluentMappings.AddFromAssemblyOf<ProvideClassFromYourOtherAssembly>();
              });

Answer 2

I know this post is bit old, but I post anyway since I didn't find any up todate posts on the subject. I guess the easiest way should be to add an attribute to each property we dont want to be persisted to a table. By add a extension that check if it has for eg. has a [NoEntity] attibute.

/// <summary>
/// Tells a single Property to not be persisted to table.
/// </summary>
public class NoEntity : Attribute { }


    /// <summary>
/// Extension to ignore attributes
/// </summary>
public static class FluentIgnore
{
    /// <summary>
    /// Ignore a single property.
    /// Property marked with this attributes will no be persisted to table.
    /// </summary>
    /// <param name="p">IPropertyIgnorer</param>
    /// <param name="propertyType">The type to ignore.</param>
    /// <returns>The property to ignore.</returns>
    public static IPropertyIgnorer SkipProperty(this IPropertyIgnorer p, Type propertyType)
    {
        return p.IgnoreProperties(x => x.MemberInfo.GetCustomAttributes(propertyType, false).Length > 0);
    }
}

And in the fluent config setup:

            return Fluently.Configure()
            .Database(DatabaseConfig)
            .Mappings(m => m.AutoMappings.Add(AutoMap.Assembly(typeof(IDependency).Assembly)
            .OverrideAll(p => {
                p.SkipProperty(typeof(NoEntity)); 
            }).Where(IsEntity)))
            .ExposeConfiguration(ValidateSchema)
            .ExposeConfiguration(BuildSchema)
            .BuildConfiguration();

Answer 3

Will not Justin. This is the thing with this extension. Just the property you want gets ignored.

public class Person : IEntity{ 
 public virtual string Name{..}
 public virtual string Lastname{..}

 [NoProperty]
 public virtual string FullName{ // Not created property
  get { return Name +  " " + Lastname;  }
 }
}

public class Group : IEntity{ 
 public virtual string FullName{..} //Created property
}