Power Platform (Dynamics) FetchXml serializer

FetchUtil.cs

using System.Xml.Linq;

namespace Playground 
{
public class FetchUtil
{
    private static readonly Type[] SimpleTypes = new Type[] { typeof(string), typeof(DateTime), typeof(Enum), typeof(decimal), typeof(Guid) };
    public static XElement ToXml(string rootName, object? x, XElement? root = null)
    {
        if (x == null) { return new XElement(rootName); }
        if (root == null) { root = new XElement(rootName); };
        if (SimpleTypes.Contains(x.GetType())) { return new XElement(rootName, x); }
        var properties = x.GetType().GetProperties();
        foreach (var property in properties)
        {
            var value = property.GetValue(x);
            if (property.PropertyType.IsPrimitive || SimpleTypes.Contains(property.PropertyType))
            {
                root.SetAttributeValue(property.Name, value);
            }
            else if (value is Array array)
            {
                for (int i = 0; i < array.Length; i++)
                {
                    root.Add(ToXml(property.Name, array.GetValue(i)));
                }
            }
            else
            {
                root.Add(value == null ? new XElement(property.Name) : ToXml(property.Name, value));
            }
        }
        return root;
    }
}
}