XSD targetNamespace

Of course, the XSD tool is also XML namespace-aware. If we specify a default namespace in the source XML document:

<?xml version=”1.0”?>

<garage xmlns="urn:GarageSchema.xsd">

<…>

xsd.exe would make the namespace the targetNamespace of the schema:

<?xml version=”1.0”?>

  <xs:schema id="NewDataSet"
    targetNamespace="urn:GarageSchema.xsd"
    xmlns:mstns="urn:GarageSchema.xsd"

    xmlns="urn:GarageSchema.xsd"

<…>

If the source document does not contain a namespace declaration you have to manually add the xmlns and targetNamespace attributes to the generated schema. If the source document references content from multiple namespaces the tool will generate a schema file for each of the referenced namespaces.

Extracting All Schema Types

The most prevalent use case for the XSD tool is to generate classes corresponding to the complexTypes in an XML schema. XML schemas are the starting point when we develop an application exchanging data through XML. As soon as both parties agreed on the data exchange format each one can go off and develop their application. XML schema is a good choice to document the format, because of it ability to express complex XML formats and the wide spread tool support, for the creation and validation of XSD, or, more important, it will also enable us to create classes automatically.

We can invoke the XML Schema Definition Tool with the /c switch from the command-line when we need to create classes for the top-level elements in the schema:

xsd.exe garage.xsd /c /l:CS

The “.xsd” extension signals that we want to create classes from a schema, the /c switch signals that we want stand-alone classes, not a typed DataSet. The /l switch specifies to language to generate the classes in. Possible choices are ‘CS’ for C#, ‘VB’ for Visual Basic.NET and ‘JS’ for Jscript. You could provide your own code emitter classes to produce classes in additional languages, but that is beyond the scope of this chapter. With the /l:CS switch we provided, the tool creates a C# source file called garage.cs. It contains classes corresponding either to the complexType of a top-level element in the input schema or a type referenced by a top-level element. Let’s run the schema from listing C.2 in the previous section through the XSD tool and examine the generated code file.

Each top-level element in the garage.xsd schema file results in a class in the source code file. The fields of the class are determined by an element’s complexType. Each xs:element or xs:attribute in the complexType definition results in a public field in the generated class. Their types are mapped to according to the standard mapping we’ve seen in Table 5.x and 5.y. If a top-level element contains an element of another complexType the tool will also produce a class for the child element’s type.

3           Listing C.3 Classes generated by the XSD tool from the schema in listing C.2

[System.Xml.Serialization.XmlRootAttribute(Namespace="",

  IsNullable=false)]

public class garage {

    public string desc;

    [System.Xml.Serialization.XmlElementAttribute("car")]

    public garageCar[] car;                                | #1

}

public class garageCar {

    [System.Xml.Serialization.XmlAttributeAttribute()]     | #2

    public string make;   

    [System.Xml.Serialization.XmlAttributeAttribute()]

    public string model;

    [System.Xml.Serialization.XmlAttributeAttribute()]

    public string year;

}

[System.Xml.Serialization.XmlRootAttribute("NewDataSet", Namespace="", IsNullable=false)]

public class NewDataSet {   

    [System.Xml.Serialization.XmlElementAttribute("garage")] |#3

    public garage[] Items;

}

(annotation) <#1 Elements with maxOccurs>1 result in an array type. >
(annotation) <#2 xs:attribute nodes in the schema result in a field with an XmlAttributeAttribute. >
(annotation) <#3 The XmlElementAttribute indicates that all items in the array are direct descendants of the NewDataSet node. >

NOTE: The tool will not produce classes for top-level elements of simpleTypes. Also, if multiple top-level elements refer to the same complexType their type, by referencing a named type instead of declaring the type inline, the tool will only generate a class the first time the complexType is referenced.