c# - 实例化一个休眠集合

Question

在我的订单实体中，我在 orderItems 上得到了一个空引用。这发生在首次创建订单时。我希望能够添加类似的内容

order.OrderItems = new Iesi.Collections.Set<OrderItem>();

错误是“无法在此处访问 protected 构造函数“Set”

    public class Order
    {
        public virtual int Id { get; set; }
        public virtual ISet<OrderItem> OrderItems { get; set; }

        public virtual void AddOrderItem(OrderItem item)
        {
            item.Order = this;
            // OrderItems below is null
            OrderItems.Add(item); 
        }

    }


<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="EStore.Domain"
                   namespace="EStore.Domain.Model">

  <class name="Order" table="Orders">
    <id name="Id" type="Int32" column="Id" unsaved-value="0">
      <generator class="identity"/>
    </id>

    <property name="UserName" column="UserName"/>
    <set name="OrderItems" table="OrderItems" generic="true" cascade="all-delete-orphan"  inverse="true" >
      <key column="OrderId" not-null="true" />
      <one-to-many class="EStore.Domain.Model.OrderItem, EStore.Domain" />
    </set>

  </class>
</hibernate-mapping>

Answer 1

在构造函数中将 OrderItems 设置为新的 List

public Order() {
 OrderItems = new List<OrderItem>();
}