ADO.NET limitation in validating XSD facets (811107)

WORKAROUND

To work around this problem, use a System.Xml.XmlValidatingReader object to validate the XML representation of the data in a DataSet against its underlying schema.

1. In Module1.vb, delete the existing code in Sub Main().
2. In Module1.vb, paste the following code in Sub Main() . Study the in-line comments that explain the newly added code to validate the XML representation of the data in the DataSet by using a System.Xml.XmlValidatingReader object:

   Dim response As String
           Try
               Dim dsEmployees As System.Data.DataSet
               dsEmployees = New DataSet()
   
               Dim employeeTable As System.Data.DataTable
   
               dsEmployees.ReadXmlSchema("c:\employee.xsd")
   
               employeeTable = dsEmployees.Tables("Employee")
   
               Dim employeeRow As System.Data.DataRow
               employeeRow = employeeTable.NewRow
   
               employeeRow("EmployeeID") = "E1"
               employeeRow("FirstName") = "Jim"
               employeeRow("MiddleInitial") = "A"
               employeeRow("LastName") = "Stanton"
               employeeRow("age") = 60
   
               dsEmployees.Tables("Employee").Rows.Add(employeeRow)
   
               'Write out the Dataset's schema to disk.
               dsEmployees.WriteXmlSchema("c:\dsEmployeesSchema.xsd")
   
               'Create an instance of an XmlValidatingReader to parse the XML representation of the Dataset's data 
               '(obtained by calling the GetXml method of the Dataset.
               Dim rdr As New System.Xml.XmlValidatingReader(dsEmployees.GetXml, System.Xml.XmlNodeType.Element, Nothing)
   
               'Add an event handler to trap validation errors.
               AddHandler rdr.ValidationEventHandler, AddressOf ValidationEvent
   
               'Create an instance of an XmlSchemaCollection object to cache the dataset's schema.
               Dim sc As New System.Xml.Schema.XmlSchemaCollection()
               rdr.ValidationType = Xml.ValidationType.Schema
   
               'Add the XmlSchemaCollection to the XmlValidatingReaders schemas collection.
               rdr.Schemas.Add(Nothing, "c:\dsEmployeesSchema.xsd")
   
               'Parse the XML data.
               'Any validation errors experienced are trapped and reported by the 
               'ValidationEvent custom sub procedure that implements the System.Xml.Schema.ValidationEventHandler delegate.
               Do While rdr.Read
   
               Loop
   
           Catch exp As Exception
               Console.WriteLine("Error occurred : " & exp.Message)
           Finally
               response = Console.ReadLine
           End Try
   

3. Add the following ValidationEvent custom Sub procedure to Module1.
   
   This procedure is an implementation of the System.Xml.Schema.ValidationEventHandler delegate. It is linked to the ValidationEventHandler event of the XmlValidatingReader object by the ADDHANDLER statement in Sub Main(). Any validation errors experienced by the XmlValidatingReader object as it parses the XML representation of the data in the DataSet appears in the Console window by the code in this procedure:

   Public Sub ValidationEvent(ByVal sender As Object, ByVal args As System.Xml.Schema.ValidationEventArgs)
           Console.WriteLine(args.Message)
   End Sub 
   

4. Save, re-build, and then run the program. You receive the following validation error message in the Console window to report the invalid value assigned to the Age column. The error message displays the location of the error as present in the source XML representation of the data in the DataSet:

   The 'age' element has an invalid value according to its data type. An error occurred at (<line>,<col>).

The limitations of this workaround are that validation errors related to constraints defined as XSD facets can be identified only after the records are added to a DataTable; the error messages to report these errors are XML based as opposed to being DataSet oriented.

To locate the source line in the XML that generated the error, write out and examine the DataSet's XML (use the GetXml and WriteXml DataSet methods).You also have to useXmlValidatingReader to validate the data. This is the only known workaround to address this bug, and it can be used effectively to validate the data before updating a target data source with data that is not valid.