How to get XmlSerializer to ignore all members of a certain type?

Question

I want to deserialize XML into the following class:

public partial class Delivery
{
    public System.Nullable<System.DateTime> sentDate { get; set; }
    public System.Nullable<System.DateTime> receivedDate { get; set; }
    public System.Nullable<System.DateTime> responseDueDate { get; set; }
}

However, the dates in the XML are not in an XmlSerializer friendly format. Based on answers to mulitple questions, I added this class:

public partial class DateSafeDelivery : Delivery
{
    [XmlElement("sentDate")]
    public string sentDateString
    {
        internal get { return sentDate.HasValue ? XmlConvert.ToString(sentDate.Value) : null; }
        set { sentDate = DateTime.Parse(value); }
    }
    [XmlElement("receivedDate")]
    public string receivedDateString
    {
        internal get { return receivedDate.HasValue ? XmlConvert.ToString(receivedDate.Value) : null; }
        set { receivedDate = DateTime.Parse(value); }
    }
    [XmlElement("responseDueDate")]
    public string responseDueDateString
    {
        internal get { return responseDueDate.HasValue ? XmlConvert.ToString(responseDueDate.Value) : null; }
        set { responseDueDate = DateTime.Parse(value); }
    }
}

I then configure my overrides:

private static XmlAttributeOverrides GetOverrides()
{
    var overrides = new XmlAttributeOverrides();
    var attributes = new XmlAttributes();
    attributes.XmlElements.Add(new XmlElementAttribute(typeof(DateSafeDelivery)));
    overrides.Add(typeof(MyParent), "Delivery", attributes);
    var ignore = new XmlAttributes { XmlIgnore = true };
    overrides.Add(typeof(DateTime?), ignore);
    return overrides;
}

This results in the following expection:

Message=The string '2010-06-12T00:00:00 -05:00' is not a valid AllXsd value.
Source=System.Xml.ReaderWriter
StackTrace:
    at System.Xml.Schema.XsdDateTime..ctor(String text, XsdDateTimeFlags kinds)
    at System.Xml.XmlConvert.ToDateTime(String s, XmlDateTimeSerializationMode dateTimeOption)
    at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderDeserializedAudit.Read1_NullableOfDateTime(Boolean checkType)
    at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderDeserializedAudit.Read15_DateSafeDelivery(Boolean isNullable, Boolean checkType)
    at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderDeserializedAudit.Read16_MyParent(Boolean isNullable, Boolean checkType)

So DateSafeDelivery is being used, but the XmlIgnore for the dates is being, well, ignored.

It will work, if I switch:

    overrides.Add(typeof(DateTime?), ignore);

with:

    new Dictionary<string, Type>()
    {
        { "sentDate", typeof(Delivery) },
        { "receivedDate", typeof(Delivery) },
        { "responseDueDate", typeof(Delivery) },
    }
        .ToList()
        .ForEach(t1 => overrides.Add(t1.Value, t1.Key, ignore));

And that's fine for one class and three properties. But I have 14 classes with a total of three dozen date properties. I know I have to add overrides for the 14 classes, but is there a way to get the serializer to ignore all DateTime properties?

I thought XmlAttributeOverrides.Add Method (Type, XmlAttributes) would do it. But it isn't working. Why? What is this method for? What does it do?

Answer 1

XmlAttributeOverrides.Add(Type, XmlAttributes) is designed to add an XML override attribute to the type itself, rather than to all properties returning values of that type. E.g. if you wanted to add an [XmlRoot("OverrideName")] attribute to DateSafeDelivery, you could do something like:

overrides.Add(typeof(DateSafeDelivery),
    new XmlAttributes { XmlRoot = new XmlRootAttribute("OverrideName") });

There is no dynamic override attribute to ignore all properties returning a given type because there is no static XML serialization attribute that can suppress serialization of all properties of a given type. The following does not even compile, because [XmlIgnore] can only be applied to a property or field:

[XmlIgnore] public class IgnoreAllInstancesOfMe { } // Fails to compile.

(As to why Microsoft did not implement support for [XmlIgnore] applied to a type - you would need to ask them.)

Thus you will need to introduce an extension method like the following:

public static partial class XmlAttributeOverridesExtensions
{
    public static XmlAttributeOverrides IgnorePropertiesOfType(this XmlAttributeOverrides overrides, Type declaringType, Type propertyType)
    {
        return overrides.IgnorePropertiesOfType(declaringType, propertyType, new HashSet<Type>());
    }

    public static XmlAttributeOverrides IgnorePropertiesOfType(this XmlAttributeOverrides overrides, Type declaringType, Type propertyType, HashSet<Type> completedTypes)
    {
        if (overrides == null || declaringType == null || propertyType == null || completedTypes == null)
            throw new ArgumentNullException();
        XmlAttributes attributes = null;
        for (; declaringType != null && declaringType != typeof(object); declaringType = declaringType.BaseType)
        {
            // Avoid duplicate overrides.
            if (!completedTypes.Add(declaringType))
                break;
            foreach (var property in declaringType.GetProperties(BindingFlags.Public | BindingFlags.DeclaredOnly | BindingFlags.Instance))
            {
                if (property.PropertyType == propertyType || Nullable.GetUnderlyingType(property.PropertyType) == propertyType)
                {
                    attributes = attributes ?? new XmlAttributes { XmlIgnore = true };
                    overrides.Add(declaringType, property.Name, attributes);
                }
            }
        }
        return overrides;
    }
}

And do:

    private static XmlAttributeOverrides GetOverrides()
    {
        var overrides = new XmlAttributeOverrides();

        var attributes = new XmlAttributes();
        attributes.XmlElements.Add(new XmlElementAttribute(typeof(DateSafeDelivery)));
        overrides.Add(typeof(MyParent), "Delivery", attributes);

        // Ignore all DateTime properties in DateSafeDelivery
        var completed = new HashSet<Type>();
        overrides.IgnorePropertiesOfType(typeof(DateSafeDelivery), typeof(DateTime), completed);
        // Add the other 14 types as required

        return overrides;
    }

Please also note that the DateString properties on DateSafeDelivery must have public get and set methods, e.g.:

public partial class DateSafeDelivery : Delivery
{
    [XmlElement("sentDate")]
    public string sentDateString
    {
        get { return sentDate.HasValue ? XmlConvert.ToString(sentDate.Value, XmlDateTimeSerializationMode.Utc) : null; }
        set { sentDate = DateTime.Parse(value); }
    }

XmlSerializer cannot serialize a property that is not fully public.

Incidentally, please note you must statically cache any XmlSerializer constructed with overrides to avoid a severe memory leak, as explained in this answer.