C# 序列化的DataContract向后兼容性

我上过这样的课：

[DataContract(Namespace = "blah")]
public class Item
{
    [DataMember(Order = 0)]
    public int Index { get; set; }

    [DataMember(Order = 1)]
    public Uri ItemSource { get; set; }

    [DataMember(Order = 2)]
    public Uri ErrorSource { get; set; }
}

我有很多它的序列化副本（在文件中）（包括一些生产文件）， 现在我的任务是将该类更改为以下内容：

[DataContract(Namespace = "blah")]
public class Item
{
    [DataMember(Order = 0)]
    public int Index { get; set; }

    [DataMember(Order = 1)]
    public ItemSourcesCollection Sources { get; set; }
}

ItemSourcesCollection所在的位置

[CollectionDataContract(ItemName = "ItemSourceItem", Namespace = "blah")]
public class ItemSourcesCollection : List<ItemSource> {}

其中ItemSourceType是

[Serializable]
public enum ItemSourceType 
{
    Data,

    Errors
}

---

问题在于向后兼容性。旧的序列化项是否可以正确反序列化？向后兼容迁移数据契约的最佳实践/模式是什么？

是的，经过一些反思，这是可能的。我在反序列化过程中手动检查以前的版本

第一次使用物品类别：

[DataContract(Namespace = "blah")]
public class Item : IExtensibleDataObject
{
    [DataMember(Order = 0)]
    public int Index { get; set; }

    [DataMember(Order = 1)]
    public ItemSourcesCollection Sources { get; set; }
}

现在，反序列化方法的棘手问题是：

    /// <summary>
    /// The deserialized.
    /// </summary>
    /// <param name="context">
    /// The streaming context.
    /// </param>
    [OnDeserialized]      
    private void Deserialized(StreamingContext context)
    {
       // reflection for backward compatibilty only
        if (this.ExtensionData == null)
        {
            return;
        }

        IList members = this.CheckForExtensionDataMembers();

        if (members == null)
        {
            return;
        }

        string value = this.GetExtensionDataMemberValue(members, "ItemSource");
        // do something with value

        value = this.GetExtensionDataMemberValue(members, "ErrorSource");
        // do something with value

    }

    /// <summary>
    /// The check for extension data members.
    /// </summary>
    /// <returns>
    /// Thel list of extension data memebers.
    /// </returns>
    private IList CheckForExtensionDataMembers()
    {
        PropertyInfo membersProperty = typeof(ExtensionDataObject).GetProperty(
            "Members", BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public);

        var members = (IList)membersProperty.GetValue(this.ExtensionData, null);

        if (members == null || members.Count <= 0)
        {
            return null;
        }

        return members;
    }

    /// <summary>
    /// The get extension data member value.
    /// </summary>
    /// <param name="members">
    /// The members.
    /// </param>
    /// <param name="dataMemberName">
    /// The data member name.
    /// </param>
    /// <returns>
    /// Returns extension data member value.
    /// </returns>
    private string GetExtensionDataMemberValue(IList members, string dataMemberName)
    {
        string innerValue = null;

        object member =
            members.Cast<object>().FirstOrDefault(
                m =>
                ((string)m.GetType().GetProperty("Name", BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public).GetValue(m, null)).Equals(
                    dataMemberName, StringComparison.InvariantCultureIgnoreCase));

        if (member != null)
        {
            PropertyInfo valueProperty = member.GetType().GetProperty("Value", BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public);

            object value = valueProperty.GetValue(member, null);

            PropertyInfo innerValueProperty = value.GetType().GetProperty("Value", BindingFlags.Public | BindingFlags.Instance | BindingFlags.Public);

            object tmp = innerValueProperty.GetValue(value, null);

            var s = tmp as string;
            if (s != null)
            {
                innerValue = s;
            }
        }

        return innerValue;
    }

//
///数据被反序列化。
/// 
/// 
///流式处理上下文。
/// 
[已序列化]
私有void反序列化（StreamingContext上下文）
{
//仅针对向后兼容性的反射
if（this.ExtensionData==null）
{
返回；
}
IList members=this.CheckForExtensionDataMembers（）；
如果（成员==null）
{
返回；
}
字符串值=this.GetExtensionDataMemberValue（成员，“ItemSource”）；
//做有价值的事
value=this.GetExtensionDataMemberValue（成员，“ErrorSource”）；
//做有价值的事
}
/// 
///检查扩展数据成员。
/// 
/// 
///扩展数据成员的列表。
/// 
私有IList CheckForExtensionDataMembers（）
{
PropertyInfo membersProperty=typeof（ExtensionDataObject）.GetProperty(
“成员”，BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public）；
var members=（IList）membersProperty.GetValue（this.ExtensionData，null）；
if（members==null | | members.Count
（（字符串）m.GetType（）.GetProperty（“名称”，BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public）.GetValue（m，null））.Equals(
dataMemberName，StringComparison.InvariantCultureIgnoreCase）；
如果（成员！=null）
{
PropertyInfo valueProperty=member.GetType（）.GetProperty（“Value”，BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public）；
对象值=valueProperty.GetValue（成员，null）；
PropertyInfo innerValueProperty=value.GetType（）.GetProperty（“value”，BindingFlags.Public | BindingFlags.Instance | BindingFlags.Public）；
对象tmp=innerValueProperty.GetValue（值，null）；
var s=作为字符串的tmp；
如果（s！=null）
{
innerValue=s；
}
}
返回内部值；
}

---

以上所有内容都将放在项目中。

非常感谢，我将尝试您的方法并在这里发布我的结果。

    /// <summary>
    /// The deserialized.
    /// </summary>
    /// <param name="context">
    /// The streaming context.
    /// </param>
    [OnDeserialized]      
    private void Deserialized(StreamingContext context)
    {
       // reflection for backward compatibilty only
        if (this.ExtensionData == null)
        {
            return;
        }

        IList members = this.CheckForExtensionDataMembers();

        if (members == null)
        {
            return;
        }

        string value = this.GetExtensionDataMemberValue(members, "ItemSource");
        // do something with value

        value = this.GetExtensionDataMemberValue(members, "ErrorSource");
        // do something with value

    }

    /// <summary>
    /// The check for extension data members.
    /// </summary>
    /// <returns>
    /// Thel list of extension data memebers.
    /// </returns>
    private IList CheckForExtensionDataMembers()
    {
        PropertyInfo membersProperty = typeof(ExtensionDataObject).GetProperty(
            "Members", BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public);

        var members = (IList)membersProperty.GetValue(this.ExtensionData, null);

        if (members == null || members.Count <= 0)
        {
            return null;
        }

        return members;
    }

    /// <summary>
    /// The get extension data member value.
    /// </summary>
    /// <param name="members">
    /// The members.
    /// </param>
    /// <param name="dataMemberName">
    /// The data member name.
    /// </param>
    /// <returns>
    /// Returns extension data member value.
    /// </returns>
    private string GetExtensionDataMemberValue(IList members, string dataMemberName)
    {
        string innerValue = null;

        object member =
            members.Cast<object>().FirstOrDefault(
                m =>
                ((string)m.GetType().GetProperty("Name", BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public).GetValue(m, null)).Equals(
                    dataMemberName, StringComparison.InvariantCultureIgnoreCase));

        if (member != null)
        {
            PropertyInfo valueProperty = member.GetType().GetProperty("Value", BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public);

            object value = valueProperty.GetValue(member, null);

            PropertyInfo innerValueProperty = value.GetType().GetProperty("Value", BindingFlags.Public | BindingFlags.Instance | BindingFlags.Public);

            object tmp = innerValueProperty.GetValue(value, null);

            var s = tmp as string;
            if (s != null)
            {
                innerValue = s;
            }
        }

        return innerValue;
    }