XmlSerializer - Serialize list elements without parent element

Question

I know that his question has already been asked and answered also, but I have kind of a different situation on which that solution isn't working. I've got an web method response xsd which I need to serialize/deserialize. Below is the snippet from that xsd which is problematic.

<xs:choice minOccurs="0">
  <xs:element name="Type1" maxOccurs="unbounded">
    <xs:complexType>
      <xs:sequence>
        <xs:element type="xs:string" name="string1"/>
        <xs:element type="xs:string" name="string2"/>
        <xs:element type="xs:boolean" name="boolean1"/>                           
      </xs:sequence>
    </xs:complexType>
  </xs:element>
  <xs:element name="Type2">
    <xs:complexType>
      <xs:sequence>
        <xs:element type="xs:float" name="float1"/>
        <xs:element type="xs:float" name="float2"/>
        <xs:element type="xs:float" name="float3"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:choice>

I've defined this choice element as shown below:

public class Type1
{
    [XmlElement(IsNullable = true)]
    public string string1 { get; set; }

    [XmlElement(IsNullable = true)]
    public string string2 { get; set; }

    public bool boolean1 { get; set; }
}

public class Type2
{
    public float float1 { get; set; }

    public float float { get; set; }

    public float float3 { get; set; }
}

[XmlElement("Type1", typeof(List<Type1>), IsNullable = true)]
[XmlElement("Type2", typeof(Type2), IsNullable = true)]
public object Type { get; set; }

The problem is when I need to serialize list of Type1 elements. I get this:

<Type1>
  <Type1>
     <string1>6185</string1>
     <string2>VW</string2>
     <boolean1>true</boolean1>
  </Type1>
  <Type1>
     <string1>6186</string1>
     <string2>AUDI</string2>
     <boolean1>true</boolean1>
  </Type1>
  <Type1>
     <string1>6187</string1>
     <string2>OPEL</string2>
     <boolean1>true</boolean1>
  </Type1>
</Type1>

when I, according to the xsd, need to get this:

<Type1>
   <string1>6185</string1>
   <string2>VW</string2>
   <boolean1>true</boolean1>
</Type1>
<Type1>
   <string1>6186</string1>
   <string2>AUDI</string2>
   <boolean1>true</boolean1>
</Type1>
<Type1>
   <string1>6187</string1>
   <string2>OPEL</string2>
   <boolean1>true</boolean1>
</Type1>

So my question is, how can I get rid of that parent element "Type1" that is encapsulating all the Type1 list elements?

Thank you!

Answer 1

In order to generate the XML you desire, you may need to change your data model somewhat.

XmlSerializer supports either a single polymorphic element, or a collection of polymorphic elements. In both cases it looks at each element's name to determine the actual type when deserializing. In your case, you want to have a collection of one type or a singleton of a second type. You have implemented this design by specifying that XmlSerializer effectively treat the collection as a singleton of type List<Type1> -- which is going to require an outer container element for the list.

Since you don't want that, you can instead specify that your Type property is a collection of polymorphic elements of each type:

    [XmlElement("Type1", typeof(Type1), IsNullable = true)]
    [XmlElement("Type2", typeof(Type2), IsNullable = true)]
    public List<object> Type

If you want to retain your current data model, you can create a proxy property that packages Type into an array, validating that the array contains either a collection of the first type or a singleton of the second:

[XmlRoot("Root")]
public class RootObject
{
    [XmlElement("Type1", typeof(Type1), IsNullable = true)]
    [XmlElement("Type2", typeof(Type2), IsNullable = true)]
    [Browsable(false), EditorBrowsable(EditorBrowsableState.Never), DebuggerBrowsable(DebuggerBrowsableState.Never)]
    public object [] TypeArray
    {
        get
        {
            if (Type == null)
                return null;
            var collection = Type as IEnumerable;
            if (collection != null)
                return collection.Cast<object>().ToArray();
            else
                return new[] { Type };
        }
        set
        {
            if (value == null)
            {
                Type = null;
                return;
            }
            var type1 = value.OfType<Type1>().ToList();
            var type2 = value.Where(t => t == null || t is Type2).Cast<Type2>().ToList();
            if (type2.Count == 1 && type1.Count == 0)
                Type = type2[0];
            else if (type1.Count == value.Length)
                Type = type1;
            else
                throw new InvalidOperationException("invalid value");
        }
    }

    [XmlIgnore]
    public object Type { get; set; }
}

Prototype fiddle .