InvalidOperationException Error Reflecting Class

Question

After read multiples posts related on this error and not found an solution to my problem, I explain it here.

I use XmlSerializer to serialize simple classes.

Here's my code:

    private void btnGenerateXml_Click(object sender, RoutedEventArgs e)
    {
        Orchard orchard = new Orchard
        {
            Recipe = new Recipe
            {
                Name = "Generated by JooWeb.Tools",
                Author = "admin",
                ExportUtc = DateTime.UtcNow
            },
            MyDatas = new MyDatas
            {
                //Test = "test"
                TrendDatas = new TrendDatas
                {
                    Id = null,
                    Status = "Published",
                    TrendDatasPart = new TrendDatasPart
                    {
                        IdSource = 0,
                        PostalCode = "1000",
                        Locality = "Test5",
                        Surface = (decimal)0.00,
                        Price = (decimal)0.00,
                        Type = "",
                        InsertDateIndicator = "",
                        UpdateDateIndicator = "",
                        GetFromDate = DateTime.Now,
                        UpdatedDate = new DateTime(1900, 1, 1)
                    },
                    CommonPart = new CommonPart
                    {
                        Owner = "/User.UserName=admin",
                        CreatedUtc = DateTime.UtcNow,
                        PublishedUtc = DateTime.UtcNow,
                        ModifiedUtc = DateTime.UtcNow
                    }
                }
            }
        };

        XmlSerializer orchardXmlSerializer = new XmlSerializer(typeof(Orchard));
        var path = @"C:\Temp\orchardFileImport_" + string.Format("{0:yyyyMMdd}", DateTime.Today) + ".xml";
        if (File.Exists(path))
            File.Delete(path);
        orchardXmlSerializer.Serialize(File.OpenWrite(path), orchard);
        MessageBox.Show("Finished");
    }
}

[XmlRoot]
public class Orchard
{
    [XmlElement]
    public Recipe Recipe { get; set; }
    [XmlElement(ElementName = "Data")]
    public MyDatas MyDatas { get; set; }
}

public class Recipe
{
    [XmlElement]
    public string Name { get; set; }
    [XmlElement]
    public string Author { get; set; }
    [XmlElement]
    public DateTime ExportUtc { get; set; }
}

public class MyDatas
{
    public MyDatas()
    {

    }

    //[XmlElement]
    //public string Test { get; set; }

    [XmlElement]
    public TrendDatas TrendDatas { get; set; }
}

public class TrendDatas
{
    [XmlAttribute]
    public string Status { get; set; }
    [XmlAttribute]
    public int? Id { get; set; }
    //[XmlIgnore]
    [XmlElement]
    public TrendDatasPart TrendDatasPart { get; set; }
    //[XmlIgnore]
    [XmlElement]
    public CommonPart CommonPart { get; set; }
}

public class TrendDatasPart
{
    [XmlAttribute]
    public int IdSource { get; set; }
    [XmlAttribute]
    public string PostalCode { get; set; }
    [XmlAttribute]
    public string Locality { get; set; }
    [XmlAttribute]
    public decimal Surface { get; set; }
    [XmlAttribute]
    public decimal Price { get; set; }
    [XmlAttribute]
    public string Type { get; set; }
    [XmlAttribute]
    public string InsertDateIndicator { get; set; }
    [XmlAttribute]
    public string UpdateDateIndicator { get; set; }
    [XmlAttribute]
    public DateTime GetFromDate { get; set; }
    [XmlAttribute]
    public DateTime UpdatedDate { get; set; }
}

public class CommonPart
{
    [XmlAttribute]
    public string Owner { get; set; }
    [XmlAttribute]
    public DateTime CreatedUtc { get; set; }
    [XmlAttribute]
    public DateTime PublishedUtc { get; set; }
    [XmlAttribute]
    public DateTime ModifiedUtc { get; set; }
}

With this code when I click on Generate xml file, I got the error InvalidOperationException There was an error reflecting type 'MergeExcelFiles.Orchard'. {"There was an error reflecting property 'MyDatas'."}

Like you see in my comments, I try to just add a string xmlElement to node MyDatas, with this change I got no error but in the xml file I don't have any node with name Data.

I don't understand why with class Recipe all look right but with node MyDatas nothing showed in xml file or got this error "InvalidOperationException".

Answer 1

You need to dig into your error message more because the reason is in the innermost exception:

System.InvalidOperationException: Cannot serialize member 'Id' of type System.Nullable`1[System.Int32]. XmlAttribute/XmlText cannot be used to encode complex types.

The issue is that you have a nullable value type as a property (TrendDatas.Id) to be serialized as an attribute and XmlSerializer does not handle these well. There are a number of workarounds listed here and here. None of them is particularly elegant. The best option might be changing the definition of Id to an element:

public class TrendDatas
{
    // ... snip ...

    [XmlElement(IsNullable = true)]
    public int? Id { get; set; }

    public bool ShouldSerializeId() { return Id.HasValue; }

    // ... snip ...
}

The ShouldSerializeId is a method that, by convention, the serializer uses to decide if the property should be serialized in the output. In the case of a null value, no element will be defined in the serialized output.