Correct XML serialization and deserialization of "mixed" types in .NET
- by Stefan
My current task involves writing a class library for processing HL7 CDA files.
These HL7 CDA files are XML files with a defined XML schema, so I used xsd.exe to generate .NET classes for XML serialization and deserialization.
The XML Schema contains various types which contain the mixed="true" attribute, specifying that an XML node of this type may contain normal text mixed with other XML nodes.
The relevant part of the XML schema for one of these types looks like this:
<xs:complexType name="StrucDoc.Paragraph" mixed="true">
<xs:sequence>
<xs:element name="caption" type="StrucDoc.Caption" minOccurs="0"/>
<xs:choice minOccurs="0" maxOccurs="unbounded">
<xs:element name="br" type="StrucDoc.Br"/>
<xs:element name="sub" type="StrucDoc.Sub"/>
<xs:element name="sup" type="StrucDoc.Sup"/>
<!-- ...other possible nodes... -->
</xs:choice>
</xs:sequence>
<xs:attribute name="ID" type="xs:ID"/>
<!-- ...other attributes... -->
</xs:complexType>
The generated code for this type looks like this:
/// <remarks/>
[System.CodeDom.Compiler.GeneratedCodeAttribute("xsd", "2.0.50727.3038")]
[System.SerializableAttribute()]
[System.Diagnostics.DebuggerStepThroughAttribute()]
[System.ComponentModel.DesignerCategoryAttribute("code")]
[System.Xml.Serialization.XmlTypeAttribute(TypeName="StrucDoc.Paragraph", Namespace="urn:hl7-org:v3")]
public partial class StrucDocParagraph {
private StrucDocCaption captionField;
private object[] itemsField;
private string[] textField;
private string idField;
// ...fields for other attributes...
/// <remarks/>
public StrucDocCaption caption {
get {
return this.captionField;
}
set {
this.captionField = value;
}
}
/// <remarks/>
[System.Xml.Serialization.XmlElementAttribute("br", typeof(StrucDocBr))]
[System.Xml.Serialization.XmlElementAttribute("sub", typeof(StrucDocSub))]
[System.Xml.Serialization.XmlElementAttribute("sup", typeof(StrucDocSup))]
// ...other possible nodes...
public object[] Items {
get {
return this.itemsField;
}
set {
this.itemsField = value;
}
}
/// <remarks/>
[System.Xml.Serialization.XmlTextAttribute()]
public string[] Text {
get {
return this.textField;
}
set {
this.textField = value;
}
}
/// <remarks/>
[System.Xml.Serialization.XmlAttributeAttribute(DataType="ID")]
public string ID {
get {
return this.idField;
}
set {
this.idField = value;
}
}
// ...properties for other attributes...
}
If I deserialize an XML element where the paragraph node looks like this:
<paragraph>first line<br /><br />third line</paragraph>
The result is that the item and text arrays are read like this:
itemsField = new object[]
{
new StrucDocBr(),
new StrucDocBr(),
};
textField = new string[]
{
"first line",
"third line",
};
From this there is no possible way to determine the exact order of the text and the other nodes.
If I serialize this again, the result looks exactly like this:
<paragraph>
<br />
<br />first linethird line
</paragraph>
The default serializer just serializes the items first and then the text.
I tried implementing IXmlSerializable on the StrucDocParagraph class so that I could control the deserialization and serialization of the content, but it's rather complex since there are so many classes involved and I didn't come to a solution yet because I don't know if the effort pays off.
Is there some kind of easy workaround to this problem, or is it even possible by doing custom serialization via IXmlSerializable?
Or should I just use XmlDocument or XmlReader/XmlWriter to process these documents?
