使用Fluent NHibernate覆盖C＃属性访问器方法的基本行为

Question

I have a bunch of C# classes which are inheriting a number of properties from an abstract base class. All of the types are mapped to a database model using Fluent NHibernate, and all of the property definitions use automatic getters and setters (the standard "get; set;" syntax). I recently found a need to provide a specific implementation for one of the accessor methods for a base type property on one of my derived types. So I created an explicit backing field for the base class property:

public abstract class BaseEntity : IBaseEntity
{
    protected bool active_field;

    ...

    public virtual bool active { get { return active_field; } set { active_field = value; } }

    ...

}

And then defined the specific getter logic for the "active" property in the derived type definition:

public override bool active
    {
        get { return active_field && (this.Expiration == null || this.Expiration < DateTime.Now); }
        set { active_field = value; }
    }

When I fire up the project, though, NHibernate throws an exception:

An exception of type 'System.InvalidOperationException' occurred in FluentNHibernate.dll but was not handled in user code. Additional information: Tried to add property 'active' when already added.

I'm guessing this has something to do with NHibernate needing to provide it's own override for the property definitions (hence why it requires the properties be declared virtual in the first place), but I'm not all that NHibernate savvy. That being the case, I'm happy to provide any other details, but don't really know what else is relevant. Is there an obvious reason why this can't work? If so, is there a simple workaround?

Answer 1

I am not exactly sure about the origin of your problem, but, trying to answer your question:

1. NHibernate needs all properties to be virtual to allow then to be lazy-loaded because it creates a proxy type of your entity type (which is an extension of your class). It needs them to be virtual so it can override them and inject a new behavior in it (fill them with the database value);
2. You do can map non-public properties and fields, but you would have to do this explicitly, follows an example on how to do it with FluentNHibernate.

Mapping a private property or field:

public class EntityMap : ClassMap<Entity>
{
    Id(e => e.Id).GeneratedBy.Identity();
    Map(Reveal.Member<Entity>("PrivatePropertyName"));
}

Now a suggestion to try to solve your problem: you can hide the property on your extended class using the new keyword (the property still needs to be virtual ).

public virtual new bool active
{
    get { return active_field && (this.Expiration == null || this.Expiration < DateTime.Now); }
    set { active_field = value; }
}