Uses DateTimeOffset to Timestamp with Timezone in Postgres from Npgsql

DateTimeOffsetConvention.cs

namespace Your.Namespace.Here {
	using FluentNHibernate.Conventions;
	using FluentNHibernate.Conventions.AcceptanceCriteria;
	using FluentNHibernate.Conventions.Inspections;
	using FluentNHibernate.Conventions.Instances;
	using System;
	class DateTimeOffsetConvention : IPropertyConvention, IPropertyConventionAcceptance {

		public void Accept(IAcceptanceCriteria<IPropertyInspector> criteria) {
			criteria.Expect(x => x.Type == typeof(DateTimeOffset));
		}

		public void Apply(IPropertyInstance instance) {
			instance.CustomType<DateTimeOffsetValueConverter>();
		}
	}
}

DateTimeOffsetValueConverter.cs

namespace Your.Namespace.Here {
	using NHibernate.SqlTypes;
	using NHibernate.UserTypes;
	using NpgsqlTypes;
	using System;
	using System.Data;
	public class DateTimeOffsetValueConverter
		: IUserType {
		public object Assemble(object cached, object owner) {
			return cached;
		}

		public object DeepCopy(object value) {
			if (value == null) return null;

			var dtoffset = (DateTimeOffset)value;
			return new DateTimeOffset(dtoffset.Ticks, dtoffset.Offset);
		}

		public object Disassemble(object value) {
			return value;
		}

		public new bool Equals(object x, object y) {
			if (x == null)
				return false;
			else
				return x.Equals(y);
		}

		public int GetHashCode(object x) {
			return x.GetHashCode();
		}

		public bool IsMutable {
			get { return false; }
		}

		public object NullSafeGet(System.Data.IDataReader rs, string[] names, object owner) {

			var ordinal = rs.GetOrdinal(names[0]);

			if (rs.IsDBNull(ordinal)) {
				return null;
			} else {
				NpgsqlTimeStampTZ timestamptz = (NpgsqlTimeStampTZ)rs.GetValue(ordinal);
				return new DateTimeOffset(timestamptz.Ticks, new TimeSpan(timestamptz.TimeZone.Hours, timestamptz.TimeZone.Minutes, timestamptz.TimeZone.Seconds));
			}
		}

		public void NullSafeSet(System.Data.IDbCommand cmd, object value, int index) {
			if (value == null) {
				(cmd.Parameters[index] as IDataParameter).Value = DBNull.Value;
				return;
			}
			var offsetDate = (DateTimeOffset)value;
			var zone = new NpgsqlTimeZone(offsetDate.Offset);
			var timestamptz = new NpgsqlTimeStampTZ(offsetDate.Year, offsetDate.Month, offsetDate.Day, offsetDate.Hour, offsetDate.Minute, offsetDate.Second, zone);
			(cmd.Parameters[index] as IDataParameter).Value = timestamptz;
		}

		public object Replace(object original, object target, object owner) {
			return original;
		}

		public Type ReturnedType {
			get { return typeof(DateTimeOffset); }
		}

		public SqlType[] SqlTypes {
			get { return new SqlType[] { new SqlType(DbType.DateTimeOffset) }; }
		}
	}
}

DateTimeValueConverter.cs

namespace Your.Namespace.Here {
	using NHibernate.SqlTypes;
	using NHibernate.UserTypes;
	using NpgsqlTypes;
	using System;
	using System.Data;
	public class TimestampValueConverter
		: IUserType {
		public object Assemble(object cached, object owner) {
			return cached;
		}

		public object DeepCopy(object value) {
			if (value == null) return null;

			var dtoffset = (DateTime)value;
			return new DateTime(dtoffset.Ticks);
		}

		public object Disassemble(object value) {
			return value;
		}

		public new bool Equals(object x, object y) {
			if (x == null)
				return false;
			else
				return x.Equals(y);
		}

		public int GetHashCode(object x) {
			return x.GetHashCode();
		}

		public bool IsMutable {
			get { return false; }
		}

		public object NullSafeGet(System.Data.IDataReader rs, string[] names, object owner) {

			var ordinal = rs.GetOrdinal(names[0]);

			if (rs.IsDBNull(ordinal)) {
				return null;
			} else {
				NpgsqlTimeStamp timestamptz = (NpgsqlTimeStamp)rs.GetValue(ordinal);
				return new DateTime(timestamptz.Ticks, DateTimeKind.Local);
			}
		}

		public void NullSafeSet(System.Data.IDbCommand cmd, object value, int index) {
			if (value == null) {
				(cmd.Parameters[index] as IDataParameter).Value = DBNull.Value;
				return;
			}
			var offsetDate = (DateTime)value;
			var timestamptz = new NpgsqlTimeStamp(offsetDate.Year, offsetDate.Month, offsetDate.Day, offsetDate.Hour, offsetDate.Minute, offsetDate.Second);
			(cmd.Parameters[index] as IDataParameter).Value = timestamptz;
		}

		public object Replace(object original, object target, object owner) {
			return original;
		}

		public Type ReturnedType {
			get { return typeof(DateTime); }
		}

		public SqlType[] SqlTypes {
			get { return new SqlType[] { new SqlType(DbType.DateTime) }; }
		}
	}
}