NHibernate实现自定义类型IUserType

这个我做的毕业设计中遇到的问题，在单选题表里存储多个选项内容！

下面是我的单选类和选项类

    public class Choice
    {
        private int index;

        public virtual int Index
        {
            get { return index; }
            set { index = value; }
        }
        private string value;

        public virtual string Value
        {
            get { return this.value; }
            set { this.value = value; }
        }
        public string GetXML()
        {
            return "<Choice index=\""+Index+"\"><![CDATA["+Value+"]]></Choice>";
        }
    }

    public class DanXuan
    {
        private long id;

        public long ID
        {
            get { return id; }
            set { id = value; }
        }
        private string content;

        public virtual string Content
        {
            get { return content; }
            set { content = value; }
        }
        private IList<Choice> choices=new List<Choice>();

        public virtual IList<Choice> Choices
        {
            get { return choices; }
            set { choices = value; }
        }
    }

下面是用来从一个字段读写选项集合的自定义类型类

    public class ChoiceList : IUserType
    {
 
        private static SqlType[] TYPES = new SqlType[] { new SqlType(DbType.String) };

        public bool IsMutable
        {
            get { return false; }
        }
        public Type ReturnedType
        {
            get { return typeof(IList<Choice>); }
        }

        public SqlType[] SqlTypes
        {
            get
            {
                return TYPES;
            }
        }

        public object DeepCopy(object value)
        {
            IList<Choice> sourceList = (IList<Choice>)value;
            IList<Choice> targetList = new List<Choice>();
            foreach (Choice choice in sourceList)
                targetList.Add(choice);
            return targetList;
        }

        public new bool Equals(object x, object y)
        {
            if (x == y) return true;
            if (x != null && y != null)
            {
                IList<Choice> listX = (IList<Choice>)x;
                IList<Choice> listY = (IList<Choice>)y;
                if (listX.Count != listY.Count) return false;
                for (int i = 0; i < listX.Count; i++)
                {
                    if (listX[i] != listY[i]) return false;
                }
                return true;
            }
            return true;
        }

        public int GetHashCode(object x)
        {
            return x.GetHashCode();
        }

        public object Assemble(object cached, object owner)
        {
            return DeepCopy(cached);
        }

        public object Disassemble(object value)
        {
            return DeepCopy(value);
        }

        public object NullSafeGet(IDataReader rs, string[] names, object owner)
        {
            string value = (string)NHibernateUtil.String.NullSafeGet(rs, names[0]);
            if (value == null)
                return null;
            else
                return ParseChoices(value);
        }

        public void NullSafeSet(IDbCommand cmd, object value, int index)
        {
            if (value != null)
            {
                string str = AssembleChoices((IList<Choice>)value);
                NHibernateUtil.String.NullSafeSet(cmd, str, index);
            }
            else
                NHibernateUtil.String.NullSafeSet(cmd, value, index);
        }

        public object Replace(object original, object target, object owner)
        {
            return original;
        }

        private IList<Choice> ParseChoices(string value)
        {
            XmlTextReader tr = new XmlTextReader(value, XmlNodeType.Element, null);
            IList<Choice> choiceList = new List<Choice>();
            while (tr.Read())
            {
                if (tr.NodeType == XmlNodeType.Element)
                {
                    Choice item = new Choice();
                    item.Index = int.Parse(tr.GetAttribute(0));

                    tr.Read();
            
                    item.Value = tr.Value;

                    choiceList.Add(item);
                }
            }


            return choiceList;
        }
        private string AssembleChoices(IList<Choice> choices)
        {
            string str="";
            foreach (Choice choice in choices)
                str += choice.GetXML();
            return str;
        }

    }

配置文件

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Test" namespace="Test">
  <class name="DanXuan" table="DanXuan" lazy="false">

    <id name="ID" column="ID">
      <generator class="identity" />
    </id>

    <property name="Content" column="QContent"/>
    <property name="Choices" column="Choices" type="Test.ChoiceList,Test"/>

  </class>
</hibernate-mapping>