引用的属性的数据协定序列化程序向前兼容性

Question

我正在尝试支持数据协定序列化程序的向前兼容性。我遇到问题的案例：

如果您有一个对象被保存为对属性的引用，而该对象是在已知类型的更高版本中添加的，它将成为一个异常。请注意，这两种类型在两个版本中都是已知的。唯一新的是其中一个对象内部的属性。

我在 samples and samples 附上了一个简单的模拟问题：

它有两个不同的项目： V1 是已部署的旧版本。 V2 是 V1 的更新版本。 V2 正在保存其数据，V1 需要能够加载 V2 保存的数据以支持向前兼容。

共有三种自定义类型： People: 有两个对象引用，Person 和 AnotherPerson 被保存在其中。

在 V1 和 V2 中：

[DataContract(Name = "People", Namespace = "Tests.FCTests")]
[KnownType(typeof(Person))]
[KnownType(typeof(AnotherPerson))]
public class People : IExtensibleDataObject
{
    [DataMember]
    public object Person { get; set; }

    [DataMember]
    public object AnotherPerson { get; set; }

    public ExtensionDataObject ExtensionData { get; set; }
}

人：有名字。

在 V1 和 V2 中：

[DataContract(Name = "Person", Namespace = "Tests.FCTests")]
public class Person : IExtensibleDataObject
{
    [DataMember]
    public string Name { get; set; }

    public ExtensionDataObject ExtensionData { get; set; }

}

AnotherPerson：有一个 Name，在 V2 中添加了对 Person (FriendPerson) 的引用。

在 V1 中：

[DataContract(Name = "AnotherPerson", Namespace = "Tests.FCTests")]
public class AnotherPerson : IExtensibleDataObject
{
    [DataMember]
    public string Name { get; set; }

    public ExtensionDataObject ExtensionData { get; set; }
}

在 V2 中：

[DataContract(Name = "AnotherPerson", Namespace = "Tests.FCTests")]
public class AnotherPerson : IExtensibleDataObject
{
    [DataMember]
    public string Name { get; set; }

    /* This is added in this version */
    [DataMember]
    public Person FriendPerson { get; set; }

    public ExtensionDataObject ExtensionData { get; set; }
}

版本 2 正在保存数据：

    static void Main(string[] args)
    {
        DataContractSerializer serializer = new DataContractSerializer(typeof(People), null, int.MaxValue, false, true, null, null);

        var people = new People();
        var person = new Person() { Name = "Person" };
        var anotherPerson = new AnotherPerson() { Name = "AnotherPerson", FriendPerson = person };

        people.Person = person;
        people.AnotherPerson = anotherPerson;

        using (var writer = new XmlTextWriter("../../../../SavedFiles/Version2Saved.xml", null) { Formatting = Formatting.Indented })
        {
            serializer.WriteObject(writer, people);
            writer.Flush();
        }

        Console.WriteLine("Save Successfull.");
        Console.ReadKey();
    }

版本 1 正在加载相同的数据：

    static void Main(string[] args)
    {
        DataContractSerializer serializer = new DataContractSerializer(typeof(People), null, int.MaxValue, false, true, null, null);

        People loadedPeople;

        using (var reader = new XmlTextReader("../../../../SavedFiles/Version2Saved.xml"))
        {
            loadedPeople = (People)serializer.ReadObject(reader);
        }

        Console.WriteLine("Load Successful.");

        Console.ReadKey();
    }

保存的数据：

<People xmlns:i="http://www.w3.org/2001/XMLSchema-instance" z:Id="1" xmlns:z="http://schemas.microsoft.com/2003/10/Serialization/" xmlns="Tests.FCTests">
  <AnotherPerson z:Id="2" i:type="AnotherPerson">
    <FriendPerson z:Id="3">
      <Name z:Id="4">Person</Name>
    </FriendPerson>
    <Name z:Id="5">AnotherPerson</Name>
  </AnotherPerson>
  <Person z:Ref="3" i:nil="true" />
</People>

当 V1 尝试加载数据时抛出此异常：

{System.Runtime.Serialization.SerializationException: Element Person from namespace Tests.FCTests cannot have child contents to be deserialized as an object. Please use XmlNode[] to deserialize this pattern of XML. ---> System.Xml.XmlException: 'Element' is an invalid XmlNodeType.
   at System.Xml.XmlReader.ReadEndElement()
   at System.Runtime.Serialization.XmlReaderDelegator.ReadEndElement()
   at System.Runtime.Serialization.ObjectDataContract.ReadXmlValue(XmlReaderDelegator reader, XmlObjectSerializerReadContext context)
   --- End of inner exception stack trace ---
   at System.Runtime.Serialization.ObjectDataContract.ReadXmlValue(XmlReaderDelegator reader, XmlObjectSerializerReadContext context)
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.ReadDataContractValue(DataContract dataContract, XmlReaderDelegator reader)
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator reader, String name, String ns, Type declaredType, DataContract& dataContract)
   at System.Runtime.Serialization.XmlObjectSerializerReadContextComplex.InternalDeserialize(XmlReaderDelegator xmlReader, Type declaredType, String name, String ns)
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.DeserializeFromExtensionData(IDataNode dataNode, Type type, String name, String ns)
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.GetExistingObject(String id, Type type, String name, String ns)
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.TryHandleNullOrRef(XmlReaderDelegator reader, Type declaredType, String name, String ns, Object& retObj)
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator reader, String name, String ns, Type declaredType, DataContract& dataContract)
   at System.Runtime.Serialization.XmlObjectSerializerReadContextComplex.InternalDeserialize(XmlReaderDelegator xmlReader, Int32 declaredTypeID, RuntimeTypeHandle declaredTypeHandle, String name, String ns)
   at ReadPeopleFromXml(XmlReaderDelegator , XmlObjectSerializerReadContext , XmlDictionaryString[] , XmlDictionaryString[] )
   at System.Runtime.Serialization.ClassDataContract.ReadXmlValue(XmlReaderDelegator xmlReader, XmlObjectSerializerReadContext context)
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.ReadDataContractValue(DataContract dataContract, XmlReaderDelegator reader)
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator reader, String name, String ns, Type declaredType, DataContract& dataContract)
   at System.Runtime.Serialization.XmlObjectSerializerReadContextComplex.InternalDeserialize(XmlReaderDelegator xmlReader, Type declaredType, DataContract dataContract, String name, String ns)
   at System.Runtime.Serialization.DataContractSerializer.InternalReadObject(XmlReaderDelegator xmlReader, Boolean verifyObjectName, DataContractResolver dataContractResolver)
   at System.Runtime.Serialization.XmlObjectSerializer.ReadObjectHandleExceptions(XmlReaderDelegator reader, Boolean verifyObjectName, DataContractResolver dataContractResolver)
   at System.Runtime.Serialization.DataContractSerializer.ReadObject(XmlReader reader)
   at Version1.Program.Main(String[] args) in C:\Users\Administrator\Desktop\Unknown types Test\Version1\Version1\Program.cs:line 17}

内部异常：

{System.Xml.XmlException: 'Element' is an invalid XmlNodeType.
   at System.Xml.XmlReader.ReadEndElement()
   at System.Runtime.Serialization.XmlReaderDelegator.ReadEndElement()
   at System.Runtime.Serialization.ObjectDataContract.ReadXmlValue(XmlReaderDelegator reader, XmlObjectSerializerReadContext context)}

我怀疑这个错误是因为对象引用了一个在扩展对象内部被反序列化的类型，并且没有任何类型。原因是，如果您在 People 中添加一个新的 Person 实例，而不是在 AnotherPerson (FriendPerson) 中引用相同的实例。

var anotherPerson = new AnotherPerson() { Name = "AnotherPerson", FriendPerson = new Person() };

然后保存的文件变成如下，一切正常：

<People xmlns:i="http://www.w3.org/2001/XMLSchema-instance" z:Id="1" xmlns:z="http://schemas.microsoft.com/2003/10/Serialization/" xmlns="Tests.FCTests">
  <AnotherPerson z:Id="2" i:type="AnotherPerson">
    <FriendPerson z:Id="3">
      <Name i:nil="true" />
    </FriendPerson>
    <Name z:Id="4">AnotherPerson</Name>
  </AnotherPerson>
  <Person z:Id="5" i:type="Person">
    <Name z:Id="6">Person</Name>
  </Person>
</People>

我尝试使用数据契约解析器、在序列化程序中动态添加已知类型和数据契约代理来解决这个问题，但是，none 它们起作用了。原因是当序列化程序反序列化 FriendPerson 时抛出异常，并且在此之前未调用代理或解析器内部的重写方法。

注意我们需要保留对象引用，删除它不是一个选项。

Answer 1

问题出在 Person 数据协定的 V2 中的字段顺序。为了向前兼容，需要在序列化文档的末尾附加新字段：

<People xmlns:i="http://www.w3.org/2001/XMLSchema-instance" z:Id="1" xmlns:z="http://schemas.microsoft.com/2003/10/Serialization/" xmlns="Tests.FCTests">
  <AnotherPerson z:Id="2" i:type="AnotherPerson">
    <FriendPerson z:Id="3">
      <Name z:Id="4">Person</Name>
    </FriendPerson>
    <Name z:Id="5">AnotherPerson</Name>
  </AnotherPerson>
  <Person z:Ref="3" i:nil="true" />
</People>

注意上面 XML 中的 "FriendPerson" 标签是如何出现在 "AnotherPerson" 段中的 "Name" 标签上方的。如果您的对象已按如下方式序列化，它将起作用：

<People xmlns:i="http://www.w3.org/2001/XMLSchema-instance" z:Id="1" xmlns:z="http://schemas.microsoft.com/2003/10/Serialization/" xmlns="Tests.FCTests">
  <AnotherPerson z:Id="2" i:type="AnotherPerson">
    <Name z:Id="5">AnotherPerson</Name>
    <FriendPerson z:Id="3">
      <Name z:Id="4">Person</Name>
    </FriendPerson>
  </AnotherPerson>
  <Person z:Ref="3" i:nil="true" />
</People>

为此，在V2"AnotherPerson"class的"FriendPerson"属性的DataMemberAttribute上指定"Order"参数如下：

[DataContract(Name = "AnotherPerson", Namespace = "Tests.FCTests")]
public class AnotherPerson : IExtensibleDataObject
{
    [DataMember]
    public string Name { get; set; }

    /* This is added in this version */
    [DataMember(Order = 2)]
    public Person FriendPerson { get; set; }

    public ExtensionDataObject ExtensionData { get; set; }
}

作为一般规则，您不应在数据合同的第一个版本中使用 "Order" 参数。对于任何较新的版本，您应该在任何新的 DataMemberAttribute 上指定 "Order" 参数，并增加指定的数字和版本号。在单个数据合约中有几个相同的 "Order" 参数值是完全合法的，例如在这个 V3 中：

[DataContract(Name = "AnotherPerson", Namespace = "Tests.FCTests")]
public class AnotherPerson : IExtensibleDataObject
{
    [DataMember]
    public string Name { get; set; }

    /* This is added in this version */
    [DataMember(Order = 2)]
    public Person FriendPerson { get; set; }

    [DataMember(Order = 3)]
    public string Remarks { get; set; }

    [DataMember(Order = 3)]
    public bool? IsMarried { get; set; }

    public ExtensionDataObject ExtensionData { get; set; }
}

P.S.: 我的回答可能来晚了，但对其他人还是有帮助的...

Answer 2

我正在与 MSDN 事件支持部门沟通，经过 2 个月的来回交流，他们的回答是：

We have engaged product group and the official word is there is a bug in IExtensibleDataObject (when cyclic references are ON).

我希望他们将此添加到文档中的某处，我希望这有助于其他人的未来发展。

引用的属性的数据协定序列化程序向前兼容性

Data Contract Serializer Forward Compatibility of properties which are referenced

c#

xml-serialization

datacontract

datacontractserializer

forward-compatibility