xaf.domain object new 在属性上的用法

有如下业务对象定义:

using System;
using System.Linq;
using System.Text;
using DevExpress.Xpo;
using DevExpress.ExpressApp;
using System.ComponentModel;
using DevExpress.ExpressApp.DC;
using DevExpress.Data.Filtering;
using DevExpress.Persistent.Base;
using System.Collections.Generic;
using DevExpress.ExpressApp.Model;
using DevExpress.Persistent.BaseImpl;
using DevExpress.Persistent.Validation;

namespace TestXPO.Module.BusinessObjects
{
　　//往来单位:供应商,客户都是此类的派生类
    [XafDefaultProperty("Name")]
    [DefaultClassOptions]
    public abstract class CompanyUnit : BaseObject
    {
        public CompanyUnit(Session s) : base(s)
        {

        }
        public string Name
        {
            get { return GetPropertyValue<string>(nameof(Name)); }
            set { SetPropertyValue(nameof(Name), value); }
        }
    }

    [DefaultClassOptions]
    [XafDefaultProperty(nameof(Address))]
    public class Customer : CompanyUnit
    {
        public Customer(Session s) : base(s)
        {

        }
        public string Address
        {
            get { return GetPropertyValue<string>(nameof(Address)); }
            set { SetPropertyValue(nameof(Address), value); }
        }
    }

    [DefaultClassOptions]
    public class Provider : CompanyUnit
    {
        public Provider(Session s) : base(s)
        {

        }

    }

    public class Dept : CompanyUnit
    {
        public Dept(Session s) : base(s)
        {

        }
    }

　　//存在某种单据基类:
　　//使用了CompanyUnit做为属性的类型
　　//在派生类中new TargetUnit重新定义此属性的类型,则可以成功
　　//可以达到使用真实类型过滤的作用.
　　//但如果使用Guid类型声明,并且派生类中用复杂类型,则不能成功
    [DefaultClassOptions]
    public class FormBase : BaseObject
    {
        public FormBase(Session session)
            : base(session)
        {
        }

        public CompanyUnit TargetUnit
        {
            get { return GetPropertyValue<CompanyUnit>(nameof(TargetUnit)); }
            set { SetPropertyValue(nameof(TargetUnit), value); }
        }
    }

    [DefaultClassOptions]
    public class PMSOrder : FormBase
    {
        public PMSOrder(Session s) : base(s)
        {

        }
        public new Provider TargetUnit
        {
            get { return GetPropertyValue<Provider>(nameof(TargetUnit)); }
            set { SetPropertyValue(nameof(TargetUnit), value); }
        }
    }

    [DefaultClassOptions]
    public class SMSOrder : FormBase
    {
        public SMSOrder(Session s) : base(s)
        {

        }
        public new Customer TargetUnit
        {
            get { return GetPropertyValue<Customer>(nameof(TargetUnit)); }
            set { SetPropertyValue(nameof(TargetUnit), value); }
        }
    }
}