private int _id;
    private string _name;
    private IList<Location> _subLocations;
    private IList<Stock> _stockList;
    private Location _parent;
    private bool _isActive;
    private bool _recommend;

    public virtual IList<Location> SubLocations
    {
        get
        {
            if (_subLocations == null)
            {
                _subLocations = new List<Location>();
            }

            return _subLocations;
        }
        set
        {
            _subLocations = value;
            OnPropertyChanged("SubLocations");
        }
    }

    // more properties ...

public class LocationMap:ClassMap<Location>
{
    public LocationMap()
    {
        Id(x => x.Id);
        Map(x => x.Name);
        Map(x => x.IsActive);
        References(x => x.Parent);

        HasMany(x => x.SubLocations).Where(x => x.IsActive == true);
        HasMany(x => x.StockList).Where(x => x.IsActive == true);

        Table("tbl_locations");

    }
}

Id   Name          IsActive  Parent_id
   1    Magazijn A       1     NULL
   2    Magazijn B       1     NULL
   3    Gang A           1      2
   4    Rek B            1          3

public IList<Location> GetAllParentLocations()
    {
        var result = NHibernateHelper.Session.CreateQuery("from Location l fetch all properties where l.Parent is null and l.IsActive = true").List<Location>();
        return (List<Location>)result ?? new List<Location>();
    }

NHibernate: select location0_.Id as Id15_, location0_.Name as Name15_,  location0_.IsActive as IsActive15_, location0_.Parent_id as Parent4_15_ from tbl_locations location0_ where (location0_.Parent_id is null) and location0_.IsActive=1
NHibernate: SELECT sublocatio0_.Location_id as Location5_1_, sublocatio0_.Id as Id1_, sublocatio0_.Id as Id15_0_, sublocatio0_.Name as Name15_0_, sublocatio0_.IsActive as IsActive15_0_, sublocatio0_.Parent_id as Parent4_15_0_ FROM tbl_locations sublocatio0_ WHERE  (sublocatio0_.IsActive = 1) and sublocatio0_.Location_id=@p0;@p0 = 1 [Type: Int32 (0)]
         NHibernate: SELECT sublocatio0_.Location_id as Location5_1_, sublocatio0_.Id as Id1_, sublocatio0_.Id as Id15_0_, sublocatio0_.Name as Name15_0_, sublocatio0_.IsActive as IsActive15_0_, sublocatio0_.Parent_id as Parent4_15_0_ FROM tbl_locations sublocatio0_ WHERE  (sublocatio0_.IsActive = 1) and sublocatio0_.Location_id=@p0;@p0 = 42 [Type: Int32 (0)]
NHibernate: SELECT sublocatio0_.Location_id as Location5_1_, sublocatio0_.Id as Id1_, sublocatio0_.Id as Id15_0_, sublocatio0_.Name as Name15_0_, sublocatio0_.IsActive as IsActive15_0_, sublocatio0_.Parent_id as Parent4_15_0_ FROM tbl_locations sublocatio0_ WHERE  (sublocatio0_.IsActive = 1) and sublocatio0_.Location_id=@p0;@p0 = 60 [Type: Int32 (0)]

HasMany(x => x.SubLocations).KeyColumns.Add("Parent_Id").Where(x => x.IsActive == true);