NHibernate.Property.Expression

A convention based expression resolver for NHibernate. If a <PropertyName>Expression exists it will be used for Linq queries.

On your data object do this:

 public class Person
    {
        public virtual Guid Id { get; set; }
        public virtual string Name { get; set; }
        public virtual DateTime StartDate { get; set; }
        public virtual DateTime? EndDate { get; set; }
        public virtual Person Manager { get; set; }

        public static Expression<Func<Person, bool>> IsActiveExpression =
            person => person.StartDate <= DateTimeTestable.Today() && (person.EndDate == null || person.EndDate >= DateTimeTestable.Today());

        public static Func<Person, bool> CompiledIsActive = IsActiveExpression.Compile(); 

        public virtual bool IsActive { get { return CompiledIsActive(this); } }
    }

The important parts are the IsActiveExpression field and the IsActive property as they are linked by convention.

To query, use 

    session.QueryExtended<Person>().Where(p => p.IsActive)

When a new NHibernate is releaset it appears it appears that it will be possible to do (in github code for NHibernate): cfg.SetProperty(Environment.QueryLinqProvider, typeof(ExpressionUnpackQueryProvider).Name)

and use the normal

  session.Query<Person>().Where(p => p.IsActive)

The sql generated by NHibernate will be something like this:

    select
        person0_.Id as Id0_,
        person0_.Name as Name0_,
        person0_.StartDate as StartDate0_,
        person0_.EndDate as EndDate0_,
        person0_.Manager as Manager0_ 
    from
        Person person0_ 
    where
        person0_.StartDate<=@p0 
        and (
            person0_.EndDate is null 
            or person0_.EndDate>=@p1
        );