Question

I would like to add a conditional property to an NHibernate entity using FluentNhibernate for mapping. I would also like to order by this property in my search criteria.

I have a list of contracts, which I would like to flag as expired or not based on the passing of the EndDate property on the contract. As for the order, I would like expired contracts to drop to the bottom of the list.

My desired outcome as a T-SQL statement;

SELECT ID, BeginDate, EndDate, CASE WHEN EndDate > GETDATE() THEN 1 ELSE 0 END AS Expired
FROM myTable
ORDER BY CASE WHEN EndDate > GETDATE() THEN 1 ELSE 0 END;

Is this possible with FluentNHibernate?

My (scrubbed) entity;

namespace MyDomain.Entities
{
    public class MyEntity
    {
        // [ID] [int] IDENTITY(1,1) NOT NULL
        public virtual int ID { get; private set; }
        // [IsDeleted] [bit] NOT NULL
        public virtual bool IsDeleted { get; set; }
        // [BeginDate] [datetime] NOT NULL
        public virtual DateTime BeginDate { get; set; }
        // [EndDate] [datetime] NOT NULL
        public virtual DateTime EndDate { get; set; }
    }
}

My mapping for that entity;

namespace MyDomain.Mappings
{
    public class MyEntityMap : ClassMap<MyEntity>
    {
        public MyEntityMap ()
        {
            this.Table("myTable");
            this.Id(x => x.ID);
            this.Map(x => x.IsDeleted);
            this.Map(x => x.BeginDate);
            this.Map(x => x.EndDate);
        }
    }
}

Answer 1

Yep. You can specify the CASE statement as a Formula:

namespace MyDomain.Mappings
{
    public class MyEntityMap : ClassMap<MyEntity>
    {
        public MyEntityMap ()
        {
            this.Table("myTable");
            this.Id(x => x.ID);
            this.Map(x => x.IsDeleted);
            this.Map(x => x.BeginDate);
            this.Map(x => x.EndDate);
            this.Map(x=>x.HasExpired)
               .Formula("CASE WHEN EndDate > GetDate() THEN 1 ELSE 0 END");
        }
    }
}

This formula is obviously get-only, but must be set into a field or property (forcing you to define said field or property with public getter and setter, unless using some other tricks to set a private backing field). In this specific case, you may be better off defining this logic in a property getter, UNLESS you need to use this calculation in a query, or you need the DB server’s local time instead of the client machine’s.