How to Optionally exclude a class member when serializing to XML

Question

I just took over a fairly large project. One of my tasks is to modify the code that gets rate quotes from FedEx. Currently, in order to get a set of rate quotes for a shipment that includes quotes for each "ServiceType" (Ground, 2-day, overnight, etc.) the code makes one call for each type. FedEx offers a web service that is used to get this information. After doing a little research, it looks like this web service can return multiple ServiceType quotes with a single round-trip. To do this, I'm supposed to "leave the service type out of the request." (Here's the question that pointed me in that direction.)

So I know that I can exclude the service type property from the serialization by decorating the property with, [System.Xml.Serialization.XmlIgnoreAttribute()]. But how can I do that only when I want results for all the ServiceType values and still be able to pass a single service type for the cases where I know what shipping method the user wants?

EDIT: FedEx's documentation indicates that this field is optional. Some basic testing shows that excluding it from the request with the XmlIgnoreAttribute does return data for multiple ServiceTypes.

Answer 1

If you implement a public bool ShouldSerializeXXX() function alongside the XXX property being serialized, XmlSerializer will ignore the corresponding XXX property when the function returns false. You'll have to have some basis for setting this (maybe the XXX property can be null? or you can grab some other state to make the decision.)

So, something along these lines:

public class MyClass
{
    public ServiceType? ServiceType { get; set; }
    public bool ShouldSerializeServiceType() { return ServiceType.HasValue; }
}