Question

I have the same problem with regard to this question. I am sending data back and forth with a SOAP-based API where the responses don’t follow the standard quite right, specifically with null values. For DateTime, the API will send back an empty string, like this:

<nextreview></nextreview>

Which causes the following error to occur on deserialization:

The string ” is not a valid AllXsd value.

So my thought was to create a custom Nullable type, NullableOrEmpty<T>, implementing IXMLSerializable that handles empty string by converting it to null. The problem is I only want to handle the exceptional case of an empty string. Everything else I want to serialize and deserialize as normal, using the ‘default’ behavior. How do I simulate the default behavior of serialization in my code below?

public class NullableOrEmpty<T> : IXmlSerializable
    where T : struct
{
    public T? NullableValue { get; set; }
    public T Value { get { return this.NullableValue.Value; } }
    public bool HasValue { get { return this.NullableValue.HasValue; } }

    ...

    public void ReadXml(XmlReader reader)
    {
        string xml = reader.ReadElementContentAsString();
        if (string.IsNullOrEmpty(xml))
        {
            this.NullableValue = null;
        }
        else
        {
            //THIS SHOULD DO THE DEFAULT. THIS DOESN'T WORK.  WHAT DO I DO??
            //this.NullableValue = (T?)new XmlSerializer(typeof(T?)).Deserialize(reader);
        }
    }

    public void WriteXml(XmlWriter writer)
    {
        //THIS SHOULD DO THE DEFAULT.  THIS DOESN'T WORK. WHAT DO I DO??
        //new XmlSerializer(typeof(T?)).Serialize(writer, this.NullableValue);
    }

}

When I say “THIS DOESN’T WORK”, it specifically generates the following error message, probably because it’s trying to consume something that isn’t there:

There is an error in XML document (63,
6).

<lastreview xmlns=''> was not
expected.

Here is a snippet of XML at that spot. The error is caused by the value in birthdate, because I’m not consuming it correctly in the non-exceptional case where the value is actually given:

<udf4></udf4>
<udf3></udf3>
<birthdate>1978-05-24Z</birthdate>
<lastreview></lastreview>
<fulltime>1</fulltime>

Any thoughts or ideas are appreciated. I can post more code samples if needed or test out suggestions. Thanks!

Answer 1

One thing you can do here, though it may be more of a pain is to implement the adapter pattern, where the object you populate from the xml result just has properties of type string, then write a converter method to populate your ‘real’ object checking for empty strings when the destination property is DateTime. It may be easier than implementing your own serializer.