Question

Consider this type:

  [DataContract]
  public class EntityId
  {
    [DataMember(Order = 1)]
    public string IdAsString { get; set; }
    [DataMember(Order = 2)]
    public Type Type { get; set; }
  }

I created an Xml serializer assembly for it. However, trying to serialize it yeilds an exception:

System.InvalidOperationException occurred
  Message=The type NC.DTO.FlowFolder was not expected. Use the XmlInclude or SoapInclude attribute to specify types that are not known statically.
  Source=NC.DTO.XmlSerializers
  StackTrace:
       at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write3_Type(String n, String ns, Type o, Boolean isNullable, Boolean needType)
  InnerException: 

Where NC.DTO.FlowFolder is actually the string representation of typeof(NC.DTO.FlowFolder) – the type NC.DTO.FlowFolder is known to the Xml serializer, what it seems to fail to serialize is the Type object itself.

The reflector reveals the failing method contents:

private void Write3_Type(string n, string ns, Type o, bool isNullable, bool needType)
{
    if (o == null)
    {
        if (isNullable)
        {
            base.WriteNullTagLiteral(n, ns);
        }
    }
    else if (!needType && (o.GetType() != typeof(Type)))
    {
        throw base.CreateUnknownTypeException(o);
    }
}

Notice the throw statement.

The stack trace is:

NC.DTO.XmlSerializers.dll!Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write3_Type(string n, string ns, System.Type o, bool isNullable, bool needType) + 0xda bytes    
NC.DTO.XmlSerializers.dll!Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write11_EntityId(string n, string ns, NC.DTO.EntityId o, bool isNullable, bool needType) + 0x2a8 bytes  
NC.DTO.XmlSerializers.dll!Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write14_FlowFolder(string n, string ns, NC.DTO.FlowFolder o, bool isNullable, bool needType) + 0x36b bytes  
NC.DTO.XmlSerializers.dll!Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write42_FlowFolder(object o) + 0xc9 bytes   
[Native to Managed Transition]  
System.Xml.dll!System.Xml.Serialization.TempAssembly.InvokeWriter(System.Xml.Serialization.XmlMapping mapping, System.Xml.XmlWriter xmlWriter, object o, System.Xml.Serialization.XmlSerializerNamespaces namespaces, string encodingStyle, string id) Line 342 + 0xb9 bytes    C#
System.Xml.dll!System.Xml.Serialization.XmlSerializer.Serialize(System.Xml.XmlWriter xmlWriter, object o, System.Xml.Serialization.XmlSerializerNamespaces namespaces, string encodingStyle, string id) Line 676 + 0xdf bytes   C#
System.Xml.dll!System.Xml.Serialization.XmlSerializer.Serialize(System.Xml.XmlWriter xmlWriter, object o, System.Xml.Serialization.XmlSerializerNamespaces namespaces, string encodingStyle) Line 646   C#
System.Xml.dll!System.Xml.Serialization.XmlSerializer.Serialize(System.Xml.XmlWriter xmlWriter, object o, System.Xml.Serialization.XmlSerializerNamespaces namespaces) Line 640 C#
System.Xml.dll!System.Xml.Serialization.XmlSerializer.Serialize(System.Xml.XmlWriter xmlWriter, object o) Line 616  C#

My question is how can I make Xml serializer happy to serialize and deserialize EntityId objects?

Thanks.

P.S.

If someone knows an alternative Xml serialization library, something that would be to XML serialization as Newtonsoft.Json to JSON serialization – please please please share.

Answer 1

xml is usually intended to be platform independent, hence why that isn’t working. You could try:

[XmlIgnore]
public Type Type { get; set; }
[XmlElement("Type")]
[Browsable(false), EditorBrowsable(EditorBrowsableState.Never)]
public string AssemblyQualifiedTypeName
{
    get { return Type == null ? null : Type.AssemblyQualifiedName; }
    set { Type = string.IsNullOrEmpty(value) ? null : Type.GetType(value); }
}

Note also that the data-contract attributes have no effect if you are using XmlSerializer. Note also that this will tie you to .NET and possibly particular versions etc.