<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="ChickenPing.Core" namespace="ChickenPing.Core">
  <class name="ChickenPing.Core.Substitution, ChickenPing.Core" table="Subs">
    <id name="ID" column="ID">
      <generator class="guid"/>
    </id>
    <property name="Ingredient" column="ingredient"  not-null="true"/>
    <property name="Substitutes" column="substitutes" not-null="true"/>
    <property name="Measurement" column="measurement"/>
    <property name="Quantity" column="quantity"/>
  </class>
</hibernate-mapping>

namespace ChickenPing.Core {
public class Substitution {
        protected Guid id;
        protected string ingredient,
                       measurement,
                       substitutes;
        protected double? quantity;

        /// <summary>
        /// Gets or sets the database ID for this substitution.
        /// </summary>
        /// <value>The database ID for this substitution.</value>
        public virtual Guid ID {
            get { return id; }
            set { id = value; }
        }

        /// <summary>
        /// Gets or sets the ingredient name.
        /// </summary>
        /// <value>The name.</value>
        public virtual string Ingredient {
            get { return ingredient; }
            set { ingredient = value; }
        }

        /// <summary>
        /// Gets or sets the name of the unit used to measure this ingredient.
        /// </summary>
        /// <value>The name of the unit used to measure this ingredient.</value>
        public virtual string Measurement {
            get { return measurement; }
            set { measurement = value; }
        }


        /// <summary>
        /// Gets or sets the quantity of the ingredient.
        /// </summary>
        /// <value>The quantity.</value>
        public virtual double? Quantity {
            get { return quantity; }
            set { quantity = value; }
        }

        /// <summary>
        /// Gets or sets the substitutes which can be used for this ingredient.
        /// </summary>
        /// <value>The substitutes which can be used for this ingredient..</value>
        public virtual string Substitutes {
            get { return substitutes; }
            set { substitutes = value; }
        }

        /// <summary>
        /// Initializes a new blank <see cref="Ingredient"/>.
        /// </summary>
        public Substitution() {
...

config.AddAssembly(typeof(Substitution).Assembly);