ParamNullValue

using System;
using NUnit.Framework;
using BLToolkit.DataAccess;

namespace HowTo.DataAccess
{
    [TestFixture]
    public class ParamNullValue
    {
        public abstract class TestAccessor : DataAccessor
        {
            public abstract Person SelectByKey([ParamNullValue(1)] int id);
        }

        [Test]
        public void Test()
        {
            TestAccessor ta = DataAccessor.CreateInstance<TestAccessor>();

            // Parameter id == 1 will be replaced with NULL
            //
            Person p1 = ta.SelectByKey(1);
            Assert.IsNull(p1);

            // Parameter id == 2 will be send as is
            //
            Person p2 = ta.SelectByKey(2);
            Assert.IsNotNull(p2);
        }
    }
}

using System;

using BLToolkit.DataAccess;
using BLToolkit.Mapping;

namespace HowTo.DataAccess
{
    public class Person
    {
        [MapField("PersonID"), PrimaryKey, NonUpdatable]
        public int    ID;

        public string LastName;
        public string FirstName;
        public string MiddleName;
        public Gender Gender;
    }
}

using System;

using BLToolkit.Mapping;

namespace HowTo.DataAccess
{
    public enum Gender
    {
        [MapValue("F")] Female,
        [MapValue("M")] Male,
        [MapValue("U")] Unknown,
        [MapValue("O")] Other
    }
}

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <appSettings>
        <add
            key   = "ConnectionString"
            value = "Server=.;Database=BLToolkitData;Integrated Security=SSPI"/>
    </appSettings>
</configuration>