Schema Validation using XPathNavigator
Using the XmlDocument class, you can validate the XML content contained in an XmlDocument object in two ways. The first way is to validate the XML content using a validating XmlReader object and the second way is to use the Validate method of the XmlDocument class. You can also perform read-only validation of XML content using the XPathDocument class.
Validating XML Data
The XmlDocument class does not validate an XML document using either DTD or XML schema definition language (XSD) schema validation by default. It only verifies that the XML document is well formed.
The first way to validate an XML document is to validate the document as it is loaded into an XmlDocument object using a validating XmlReader object. The second way is to validate a previously untyped XML document using the Validate method of the XmlDocument class. In both cases, changes to the validated XML document can be revalidated using the Validate method of the XmlDocument class.
Validating a Document as it is Loaded
A validating XmlReader object is created by passing an XmlReaderSettings object to the Create method of the XmlReader class that takes an XmlReaderSettings object as a parameter. The XmlReaderSettings object passed as a parameter has a ValidationType property set to Schema and an XML Schema for the XML document contained in the XmlDocument object added to its Schemas property. The validating XmlReader object is then used to create the XmlDocument object.
The following example validates the contosoBooks.xml file as it is loaded into the XmlDocument object by creating the XmlDocument object using a validating XmlReader object. Because the XML document is valid according to its schema, no schema validation errors or warnings are generated.
Imports System
Imports System.Xml
Imports System.Xml.Schema
Imports System.Xml.XPath
Class ValidatingReaderExample
Shared Sub Main(ByVal args() As String)
Try
Dim settings As XmlReaderSettings = New XmlReaderSettings()
settings.Schemas.Add("https://www.contoso.com/books", "contosoBooks.xsd")
settings.ValidationType = ValidationType.Schema
Dim reader As XmlReader = XmlReader.Create("contosoBooks.xml", settings)
Dim document As XmlDocument = New XmlDocument()
document.Load(reader)
Dim navigator As XPathNavigator = document.CreateNavigator()
Catch e As Exception
Console.WriteLine("ValidatingReaderExample.Exception: {0}", e.Message)
End Try
End Sub
Shared Sub SchemaValidationHandler(ByVal sender As Object, ByVal e As ValidationEventArgs)
Select Case e.Severity
Case XmlSeverityType.Error
Console.WriteLine("Schema Validation Error: {0}", e.Message)
Exit Sub
Case XmlSeverityType.Warning
Console.WriteLine("Schema Validation Warning: {0}", e.Message)
Exit Sub
End Select
End Sub
End Class
using System;
using System.Xml;
using System.Xml.Schema;
using System.Xml.XPath;
class ValidatingReaderExample
{
static void Main(string[] args)
{
try
{
XmlReaderSettings settings = new XmlReaderSettings();
settings.Schemas.Add("https://www.contoso.com/books", "contosoBooks.xsd");
settings.ValidationType = ValidationType.Schema;
XmlReader reader = XmlReader.Create("contosoBooks.xml", settings);
XmlDocument document = new XmlDocument();
document.Load(reader);
XPathNavigator navigator = document.CreateNavigator();
}
catch (Exception e)
{
Console.WriteLine("ValidatingReaderExample.Exception: {0}", e.Message);
}
}
static void SchemaValidationHandler(object sender, ValidationEventArgs e)
{
switch (e.Severity)
{
case XmlSeverityType.Error:
Console.WriteLine("Schema Validation Error: {0}", e.Message);
break;
case XmlSeverityType.Warning:
Console.WriteLine("Schema Validation Warning: {0}", e.Message);
break;
}
}
}
The example takes the contosoBooks.xml file as an input.
<bookstore xmlns="https://www.contoso.com/books">
<book genre="autobiography" publicationdate="1981-03-22" ISBN="1-861003-11-0">
<title>The Autobiography of Benjamin Franklin</title>
<author>
<first-name>Benjamin</first-name>
<last-name>Franklin</last-name>
</author>
<price>8.99</price>
</book>
<book genre="novel" publicationdate="1967-11-17" ISBN="0-201-63361-2">
<title>The Confidence Man</title>
<author>
<first-name>Herman</first-name>
<last-name>Melville</last-name>
</author>
<price>11.99</price>
</book>
<book genre="philosophy" publicationdate="1991-02-15" ISBN="1-861001-57-6">
<title>The Gorgias</title>
<author>
<name>Plato</name>
</author>
<price>9.99</price>
</book>
</bookstore>
The example also takes the contosoBooks.xsd as an input.
<?xml version="1.0" encoding="utf-8"?>
<xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="https://www.contoso.com/books" xmlns:xs="https://www.w3.org/2001/XMLSchema">
<xs:element name="bookstore">
<xs:complexType>
<xs:sequence>
<xs:element maxOccurs="unbounded" name="book">
<xs:complexType>
<xs:sequence>
<xs:element name="title" type="xs:string" />
<xs:element name="author">
<xs:complexType>
<xs:sequence>
<xs:element minOccurs="0" name="name" type="xs:string" />
<xs:element minOccurs="0" name="first-name" type="xs:string" />
<xs:element minOccurs="0" name="last-name" type="xs:string" />
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="price" type="xs:decimal" />
</xs:sequence>
<xs:attribute name="genre" type="xs:string" use="required" />
<xs:attribute name="publicationdate" type="xs:date" use="required" />
<xs:attribute name="ISBN" type="xs:string" use="required" />
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
In the example above, if an element or attribute is specified as having a simple type according to its schema and is loaded from a validating XmlReader object but actually has an invalid value for its type in the XML document, the value of that element or attribute is null. This occurs because the XmlDocument class uses the ReadTypedValue method of the XmlReader object to get the typed value of the element or attribute, and in the case where a ValidationEventHandler is provided the ReadTypedValue method returns null if the value is invalid according to its type.
Note
When an XML document is loaded into an XmlDocument object with an associated schema that defines default values, the XmlDocument object treats these defaults as if they appeared in the XML document. This means that the IsEmptyElement property always returns false for an element that was defaulted from the schema, even if in the XML document it was written as an empty element.
Validating a Document using the Validate Method
The Validate method of the XmlDocument class validates the XML document contained in an XmlDocument object against the schemas specified in the XmlDocument object's Schemas property and performs infoset augmentation. The result is a previously untyped XML document in the XmlDocument object replaced with a typed document.
The XmlDocument object reports schema validation errors and warnings using the ValidationEventHandler delegate passed as a parameter to the Validate method.
The following example validates the contosoBooks.xml file contained in the XmlDocument object against the contosoBooks.xsd schema contained in the XmlDocument object's Schemas property.
Imports System
Imports System.Xml
Imports System.Xml.Schema
Imports System.Xml.XPath
Class ValidateExample
Shared Sub Main(ByVal args() As String)
Dim document As XmlDocument = New XmlDocument()
document.Load("contosoBooks.xml")
Dim navigator As XPathNavigator = document.CreateNavigator()
document.Schemas.Add("https://www.contoso.com/books", "contosoBooks.xsd")
Dim validation As ValidationEventHandler = New ValidationEventHandler(AddressOf SchemaValidationHandler)
document.Validate(validation)
End Sub
Shared Sub SchemaValidationHandler(ByVal sender As Object, ByVal e As ValidationEventArgs)
Select Case e.Severity
Case XmlSeverityType.Error
Console.WriteLine("Schema Validation Error: {0}", e.Message)
Exit Sub
Case XmlSeverityType.Warning
Console.WriteLine("Schema Validation Warning: {0}", e.Message)
Exit Sub
End Select
End Sub
End Class
using System;
using System.Xml;
using System.Xml.Schema;
using System.Xml.XPath;
class ValidateExample
{
static void Main(string[] args)
{
XmlDocument document = new XmlDocument();
document.Load("contosoBooks.xml");
XPathNavigator navigator = document.CreateNavigator();
document.Schemas.Add("https://www.contoso.com/books", "contosoBooks.xsd");
ValidationEventHandler validation = new ValidationEventHandler(SchemaValidationHandler);
document.Validate(validation);
}
static void SchemaValidationHandler(object sender, ValidationEventArgs e)
{
switch (e.Severity)
{
case XmlSeverityType.Error:
Console.WriteLine("Schema Validation Error: {0}", e.Message);
break;
case XmlSeverityType.Warning:
Console.WriteLine("Schema Validation Warning: {0}", e.Message);
break;
}
}
}
The example takes the contosoBooks.xml file as an input.
<bookstore xmlns="https://www.contoso.com/books">
<book genre="autobiography" publicationdate="1981-03-22" ISBN="1-861003-11-0">
<title>The Autobiography of Benjamin Franklin</title>
<author>
<first-name>Benjamin</first-name>
<last-name>Franklin</last-name>
</author>
<price>8.99</price>
</book>
<book genre="novel" publicationdate="1967-11-17" ISBN="0-201-63361-2">
<title>The Confidence Man</title>
<author>
<first-name>Herman</first-name>
<last-name>Melville</last-name>
</author>
<price>11.99</price>
</book>
<book genre="philosophy" publicationdate="1991-02-15" ISBN="1-861001-57-6">
<title>The Gorgias</title>
<author>
<name>Plato</name>
</author>
<price>9.99</price>
</book>
</bookstore>
The example also takes the contosoBooks.xsd as an input.
<?xml version="1.0" encoding="utf-8"?>
<xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="https://www.contoso.com/books" xmlns:xs="https://www.w3.org/2001/XMLSchema">
<xs:element name="bookstore">
<xs:complexType>
<xs:sequence>
<xs:element maxOccurs="unbounded" name="book">
<xs:complexType>
<xs:sequence>
<xs:element name="title" type="xs:string" />
<xs:element name="author">
<xs:complexType>
<xs:sequence>
<xs:element minOccurs="0" name="name" type="xs:string" />
<xs:element minOccurs="0" name="first-name" type="xs:string" />
<xs:element minOccurs="0" name="last-name" type="xs:string" />
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="price" type="xs:decimal" />
</xs:sequence>
<xs:attribute name="genre" type="xs:string" use="required" />
<xs:attribute name="publicationdate" type="xs:date" use="required" />
<xs:attribute name="ISBN" type="xs:string" use="required" />
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
Validating Modifications
After modifications are made to an XML document, you can validate the modifications against the schema for the XML document using the Validate method of the XmlDocument class.
The following example validates the contosoBooks.xml file as it is loaded into the XmlDocument object by creating the XmlDocument object using a validating XmlReader object. The XML document is validated successfully as it is loaded without generating any schema validation errors or warnings. The example then makes two modifications to the XML document that are invalid according to the contosoBooks.xsd schema. The first modification inserts an invalid child element resulting in a schema validation error, and the second modification sets the value of a typed node to a value that is invalid according to the type of the node resulting in an exception.
Imports System
Imports System.Xml
Imports System.Xml.Schema
Imports System.Xml.XPath
Class ValidatingReaderExample
Shared Sub Main(ByVal args() As String)
Try
Dim settings As XmlReaderSettings = New XmlReaderSettings()
settings.Schemas.Add("https://www.contoso.com/books", "contosoBooks.xsd")
settings.ValidationType = ValidationType.Schema
Dim reader As XmlReader = XmlReader.Create("contosoBooks.xml", settings)
Dim document As XmlDocument = New XmlDocument()
document.Load(reader)
Dim navigator As XPathNavigator = document.CreateNavigator()
Dim validation As ValidationEventHandler = New ValidationEventHandler(AddressOf SchemaValidationHandler)
navigator.MoveToChild("bookstore", "https://www.contoso.com/books")
navigator.MoveToChild("book", "https://www.contoso.com/books")
navigator.MoveToChild("author", "https://www.contoso.com/books")
navigator.AppendChild("<title>Book Title</title>")
document.Validate(validation)
navigator.MoveToParent()
navigator.MoveToChild("price", "https://www.contoso.com/books")
navigator.SetTypedValue(DateTime.Now)
Catch e As Exception
Console.WriteLine("ValidatingReaderExample.Exception: {0}", e.Message)
End Try
End Sub
Shared Sub SchemaValidationHandler(ByVal sender As Object, ByVal e As ValidationEventArgs)
Select Case e.Severity
Case XmlSeverityType.Error
Console.WriteLine("Schema Validation Error: {0}", e.Message)
Exit Sub
Case XmlSeverityType.Warning
Console.WriteLine("Schema Validation Warning: {0}", e.Message)
Exit Sub
End Select
End Sub
End Class
using System;
using System.Xml;
using System.Xml.Schema;
using System.Xml.XPath;
class ValidatingReaderExample
{
static void Main(string[] args)
{
try
{
XmlReaderSettings settings = new XmlReaderSettings();
settings.Schemas.Add("https://www.contoso.com/books", "contosoBooks.xsd");
settings.ValidationType = ValidationType.Schema;
XmlReader reader = XmlReader.Create("contosoBooks.xml", settings);
XmlDocument document = new XmlDocument();
document.Load(reader);
XPathNavigator navigator = document.CreateNavigator();
ValidationEventHandler validation = new ValidationEventHandler(SchemaValidationHandler);
navigator.MoveToChild("bookstore", "https://www.contoso.com/books");
navigator.MoveToChild("book", "https://www.contoso.com/books");
navigator.MoveToChild("author", "https://www.contoso.com/books");
navigator.AppendChild("<title>Book Title</title>");
document.Validate(validation);
navigator.MoveToParent();
navigator.MoveToChild("price", "https://www.contoso.com/books");
navigator.SetTypedValue(DateTime.Now);
}
catch (Exception e)
{
Console.WriteLine("ValidatingReaderExample.Exception: {0}", e.Message);
}
}
static void SchemaValidationHandler(object sender, ValidationEventArgs e)
{
switch (e.Severity)
{
case XmlSeverityType.Error:
Console.WriteLine("Schema Validation Error: {0}", e.Message);
break;
case XmlSeverityType.Warning:
Console.WriteLine("Schema Validation Warning: {0}", e.Message);
break;
}
}
}
The example takes the contosoBooks.xml file as an input.
<bookstore xmlns="https://www.contoso.com/books">
<book genre="autobiography" publicationdate="1981-03-22" ISBN="1-861003-11-0">
<title>The Autobiography of Benjamin Franklin</title>
<author>
<first-name>Benjamin</first-name>
<last-name>Franklin</last-name>
</author>
<price>8.99</price>
</book>
<book genre="novel" publicationdate="1967-11-17" ISBN="0-201-63361-2">
<title>The Confidence Man</title>
<author>
<first-name>Herman</first-name>
<last-name>Melville</last-name>
</author>
<price>11.99</price>
</book>
<book genre="philosophy" publicationdate="1991-02-15" ISBN="1-861001-57-6">
<title>The Gorgias</title>
<author>
<name>Plato</name>
</author>
<price>9.99</price>
</book>
</bookstore>
The example also takes the contosoBooks.xsd as an input.
<?xml version="1.0" encoding="utf-8"?>
<xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="https://www.contoso.com/books" xmlns:xs="https://www.w3.org/2001/XMLSchema">
<xs:element name="bookstore">
<xs:complexType>
<xs:sequence>
<xs:element maxOccurs="unbounded" name="book">
<xs:complexType>
<xs:sequence>
<xs:element name="title" type="xs:string" />
<xs:element name="author">
<xs:complexType>
<xs:sequence>
<xs:element minOccurs="0" name="name" type="xs:string" />
<xs:element minOccurs="0" name="first-name" type="xs:string" />
<xs:element minOccurs="0" name="last-name" type="xs:string" />
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="price" type="xs:decimal" />
</xs:sequence>
<xs:attribute name="genre" type="xs:string" use="required" />
<xs:attribute name="publicationdate" type="xs:date" use="required" />
<xs:attribute name="ISBN" type="xs:string" use="required" />
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
In the example above, two modifications are made to the XML document contained in the XmlDocument object. As the XML document was loaded, any schema validation errors encountered would have been handled by the validation event handler method and written to the console.
In this example, the validation errors were introduced after the XML document was loaded and were found using the Validate method of the XmlDocument class.
Modifications made using the SetTypedValue method of the XPathNavigator class resulted in an InvalidCastException because the new value was invalid according to the schema type of the node.
For more information about modifying values using the SetTypedValue method, see the Modify XML Data using XPathNavigator topic.
Read-Only Validation
The XPathDocument class is a read-only, in-memory representation of an XML document. Both the XPathDocument class and the XmlDocument class create XPathNavigator objects to navigate and edit XML documents. Because the XPathDocument class is a read-only class, XPathNavigator object's returned from XPathDocument objects cannot edit the XML document contained in the XPathDocument object.
In the case of validation, you can create an XPathDocument object just like you create an XmlDocument object using a validating XmlReader object as described earlier in this topic. The XPathDocument object validates the XML document as it is loaded, but because you cannot edit the XML data in the XPathDocument object, you cannot revalidate the XML document.
For more information about read-only and editable XPathNavigator objects, see the Reading XML Data using XPathDocument and XmlDocument topic.
See Also
Reference
XmlDocument
XPathDocument
XPathNavigator
Concepts
Process XML Data Using the XPath Data Model
Reading XML Data using XPathDocument and XmlDocument
Selecting, Evaluating and Matching XML Data using XPathNavigator
Accessing XML Data using XPathNavigator
Editing XML Data using XPathNavigator