DataContractSerializer: Deserialized object with reference id 'xyz' not found in stream. How to recover data?

Question

I have persisted an array of objects to a file using DataContractSerializer. It has been working fine until recently when I started getting the following message.

Deserialized object with reference id '15' not found in stream
   bei System.Runtime.Serialization.XmlObjectSerializerReadContext.GetExistingObject(String id, Type type, String name, String ns)
   bei ReadAbgleichSettingsFromXml(XmlReaderDelegator , XmlObjectSerializerReadContext , XmlDictionaryString[] , XmlDictionaryString[] )
   bei System.Runtime.Serialization.ClassDataContract.ReadXmlValue(XmlReaderDelegator xmlReader, XmlObjectSerializerReadContext context)
   bei System.Runtime.Serialization.XmlObjectSerializerReadContext.ReadDataContractValue(DataContract dataContract, XmlReaderDelegator reader)
   bei System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator reader, String name, String ns, Type declaredType, DataContract& dataContract)
   bei System.Runtime.Serialization.XmlObjectSerializerReadContextComplex.InternalDeserialize(XmlReaderDelegator xmlReader, Int32 declaredTypeID, RuntimeTypeHandle declaredTypeHandle, String name, String ns)
   bei ReadUnitOfTestFromXml(XmlReaderDelegator , XmlObjectSerializerReadContext , XmlDictionaryString[] , XmlDictionaryString[] )
   bei System.Runtime.Serialization.ClassDataContract.ReadXmlValue(XmlReaderDelegator xmlReader, XmlObjectSerializerReadContext context)
   bei System.Runtime.Serialization.XmlObjectSerializerReadContext.ReadDataContractValue(DataContract dataContract, XmlReaderDelegator reader)
   bei System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator reader, String name, String ns, Type declaredType, DataContract& dataContract)
   bei System.Runtime.Serialization.XmlObjectSerializerReadContextComplex.InternalDeserialize(XmlReaderDelegator xmlReader, Int32 declaredTypeID, RuntimeTypeHandle declaredTypeHandle, String name, String ns)
   bei ReadArrayOfBaseModuleFromXml(XmlReaderDelegator , XmlObjectSerializerReadContext , XmlDictionaryString , XmlDictionaryString , CollectionDataContract )
   bei System.Runtime.Serialization.CollectionDataContract.ReadXmlValue(XmlReaderDelegator xmlReader, XmlObjectSerializerReadContext context)
   bei System.Runtime.Serialization.XmlObjectSerializerReadContext.ReadDataContractValue(DataContract dataContract, XmlReaderDelegator reader)
   bei System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator reader, String name, String ns, Type declaredType, DataContract& dataContract)
   bei System.Runtime.Serialization.XmlObjectSerializerReadContextComplex.InternalDeserialize(XmlReaderDelegator xmlReader, Type declaredType, DataContract dataContract, String name, String ns)
   bei System.Runtime.Serialization.DataContractSerializer.InternalReadObject(XmlReaderDelegator xmlReader, Boolean verifyObjectName, DataContractResolver dataContractResolver)
   bei System.Runtime.Serialization.XmlObjectSerializer.ReadObjectHandleExceptions(XmlReaderDelegator reader, Boolean verifyObjectName, DataContractResolver dataContractResolver)
   bei System.Runtime.Serialization.DataContractSerializer.ReadObject(XmlReader reader)
   bei Pruef.Net.Model.ModuleManager.LoadModules() in D:\\my_workspaces\\visualstudioprojects\\Pruef.Net\\Pruef.Net\\PruefMvvm\\Model\\ModuleManager.cs:Zeile 626.

The problem appears to be associated with the class AbgleichSettings.

    [DataContract(Name = "AbgleichSettings")]
public class AbgleichSettings
{
    #region PROPERTIES
    /// <summary>
    /// Enable feature
    /// </summary>
    [DataMember(Name = "IsEnabled")]
    public bool IsEnabled { get; set; }

    /// <summary>
    /// Display units after value
    /// </summary>
    [DataMember(Name="Units", IsRequired=false)]
    public string Units { get; set; }

    /// <summary>
    /// Multiply value by factor
    /// </summary>
    [DataMember(Name = "Factor")]
    public double Factor { get; set; }

    /// <summary>
    /// Show decimal places 0-3
    /// </summary>
    [DataMember(Name = "DecimalPlaces")]
    public int DecimalPlaces { get; set; }
    #endregion

    [OnDeserializing]
    void OnDeserializing(StreamingContext context)
    {
        IsEnabled = false;
        Units = "";
        Factor = 1;
        DecimalPlaces = 0;
    }

    public AbgleichSettings()
    {
        IsEnabled = false;
        Units = "";
        Factor = 1;
        DecimalPlaces = 0;
    }

}

Note the DataMember.Name attributes were added later as I attempted to solve the problem.

I looked in the XML and saw that the object with Id="15" is a {Comment} element which is a string property in a different class.

<Header>
  <ChangeInfo z:Id="14">
    <Author i:nil="true" />
    <Comment z:Id="15"></Comment>
    <Date>0001-01-01T00:00:00</Date>
  </ChangeInfo>
</Header>
....
<Abgleich z:Id="34">
  <DecimalPlaces>0</DecimalPlaces>
  <Factor>1</Factor>
  <IsEnabled>false</IsEnabled>
  <Units z:Ref="15" i:nil="true" />
</Abgleich>

** Serializer **

return new DataContractSerializer(Modules.GetType(), null,
                int.MaxValue /*maxItemsInObjectGraph*/,
                true /*ignoreExtensionDataObject*/,
                true /*preserveObjectReferences : this is where the magic happens */,
                null /*dataContractSurrogate*/);

What might have gone wrong here? What can I do to recover from this error?

Thanks!

Answer 1

After some experimentation, I have been able to get it working again but I don't understand exactly what the problem is.

The class 'ModuleHeader' originally just had the attribute [Serializable] and its properties had the attribute [DataMember]. Recently, I added [DataContract] to the class (seemed appropriate) and this is what caused the problem. In the OnSerialized event I noticed that the instance had not been initialised and therefore the object with the missing Id was not being created. Once I removed the [DataContract] attribute the deserialization started working again.

I will post a new question...