How to Populate a Set Collection of Children from HierarchyId in nHibernate

Question

I have the parent side of the mapping, but am unsure how to properly map the children side.

Parent Mapping

<many-to-one name="Parent" class="NHibernate.Map.OrganizationUnit, CentralDataLayer">
    <formula>(
        SELECT o.`ou_id`
        FROM `global`.`wmtb_orgunit` o
        WHERE o.`ou_hid` = `ou_hid`.GetAncestor(1)
    )</formula>
</many-to-one>

I think the children would map like this. How is possible to populate the parent HierarchyId into the where clause?

Children Mapping

<set name="Children" inverse="true" cascade="all" where="`ou_hid` != :HierarchyId and `ou_hid`.IsDescendantOf(:HierarchyId) = 1">
    <key column="`ou_hid`" />
    <one-to-many class="NHibernate.Map.OrganizationUnit, CentralDataLayer" />
</set>

Answer 1

I believe I've determined the best way to populate the direct descendants of a HierarchyId. In order for this functionality to work, a filter needs to be created on the class and a method of the class will run to query the descendants.

Further information on setting up HierarchyId support in NHibernate.

Children Mapping

<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>

Class Object

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
    }
}