HierarchyIdの直接の子孫にデータを入力するための最良の方法を決定したと思います。この機能を機能させるには、クラスにフィルターを作成する必要があり、クラスのメソッドを実行して子孫を照会します。
NHibernateでのHierarchyIdサポートの設定に関する詳細情報。
子のマッピング
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="CentralDataLayer" namespace="NHibernate.Map" schema="`global`">
    <class name="NHibernate.Map.OrganizationUnit, CentralDataLayer" table="`orgunit`">
        ...
        <property name="HierarchyId" column="`ou_hid`" type="NHibernate.UserTypes.HierarchyId, CentralDataLayer" not-null="true" />
        <filter name="FilterChildren" condition="`ou_hid`.IsDescendantOf(:HierarchyId) = 1 and `ou_hid`.GetLevel() = :HierarchyIdLevel" />
    </class>
    <filter-def name="FilterChildren">
        <filter-param name="HierarchyId" type="NHibernate.UserTypes.HierarchyId, CentralDataLayer" />
        <filter-param name="HierarchyIdLevel" type="Int16" />
    </filter-def>
</hibernate-mapping>
クラスオブジェクト
namespace NHibernate.Map
{
    using Criterion;
    using Microsoft.SqlServer.Types;
    using NHibernate;
    using System.Collections.Generic;
    public partial class OrganizationUnit
    {
        #region Fields
        private SqlHierarchyId _hierarchyId;
        private ICollection<OrganizationUnit> _children;
        #endregion Fields
        #region Properties
        /// <summary>
        ///     Hierarchy Id
        /// </summary>
        [Description("Get the OrganizationUnit hierarchy id.")]
        public virtual SqlHierarchyId HierarchyId
        {
            get { return _hierarchyId; }
            protected internal set { _hierarchyId = value; }
        }
        #endregion Properties
        #region Public Methods
        /// <summary>
        ///     Get all direct child OrganizationUnits of current OrganizationUnit.
        /// </summary>
        /// <param name="provider">The DataProvider houseing the current Session</param>
        /// <returns></returns>
        public virtual ICollection<OrganizationUnit> GetChildren(ISession session)
        {
            if (_children.IsDefault()) {
                // Enable Filter
                session
                    .EnableFilter("FilterChildren")
                    .SetParameter("HierarchyId", HierarchyId)
                    .SetParameter("HierarchyIdLevel", (short)(HierarchyId.GetLevel() + 1));
                // Collect Direct Children
                _children = session.QueryOver<OrganizationUnit>().List();
                // Disable Filter
                session.DisableFilter("FilterChildren");
            }
            return _children;
        }
        #endregion Public Methods
    }
}