Using Functional Construction to Create XML Documents

Listing 4: The complete sample program listing.

Imports System.Data
Imports System.Data.SqlClient
Imports System.Runtime.CompilerServices
Imports System.Text
Imports System.Reflection

Module Module1

   Sub Main()
      Dim customers As List(Of Customer) = GetCustomers()
      'Console.WriteLine(customers.Take(5).Dump)
      'Console.ReadLine()

      Dim xml = ConstructXMLDocument(customers.Take(5))
      Console.WriteLine(xml)
      Console.ReadLine()
   End Sub

   Function ConstructXMLDocument(ByVal list _
      As IEnumerable(Of Customer)) _
      As XElement

      Return New XElement("Customers", _
         From customer In list _
         Select New XElement("Customer", _
            New XElement("CustomerID", customer.CustomerID), _
            New XElement("TerritoryID", customer.TerritoryID), _
            New XElement("AccountNumber", _
               customer.AccountNumber), _
            New XElement("rowguid", customer.RowGuid), _
            New XElement("ModifiedDate", customer.ModifiedDate)))

   End Function

   Private Function GetCustomers() As List(Of Customer)
      Dim connectionString As String = _
         "Data Source=.\SQLExpress;Initial Catalog=AdventureWorks;" + _
         "Integrated Security=True"

      Dim customers As List(Of Customer) = New List(Of Customer)
      Using connection As SqlConnection = _
         New SqlConnection(connectionString)
         connection.Open()
         Dim command As SqlCommand = New SqlCommand( _
            "SELECT * FROM Sales.Customer", connection)

         Dim reader As SqlDataReader = command.ExecuteReader

         While (reader.Read())
            customers.Add(New Customer().Create(reader))
         End While

      End Using

      Return customers
   End Function

   <Extension()> _
   Public Function Dump(ByVal list As IEnumerable(Of Customer)) _
      As String
      Dim builder As StringBuilder = New StringBuilder()
      For Each customer As Customer In list
         builder.Append(customer.Dump())
         builder.AppendLine()
      Next
      Return builder.ToString()
   span style='color:blue'>End Function

   <Extension()> _
   Public Function Dump(ByVal customer As Customer) As String
      Dim builder As StringBuilder = New StringBuilder()
      Dim info() As PropertyInfo = _
         customer.GetType().GetProperties()

      For Each prop As Propertyinfo In info
         Try
            Console.WriteLine("Name: {0}, Value: {1}", _
                              prop.Name, _
                              prop.GetValue(customer, Nothing))

         Catch ex As Exception
            Console.WriteLine("Name: {0}, Value: {1}", _
                              prop.Name, "none")
         End Try
      Next

      Return builder.ToString()

   End Function

   <Extension()> _
   Public Function Create(ByVal customer As Customer, _
                          ByVal reader _
                          As SqlDataReader) As Customer

      customer.AccountNumber = customer.SafeRead(reader, _
         "AccountNumber", "")
      customer.CustomerID = customer.SafeRead(reader, _
         "CustomerID", -1)
      customer.TerritoryID = customer.SafeRead(reader, _
         "TerritoryID", -1)
      customer.CustomerType = customer.SafeRead(reader, _
         "CustomerType", "S")
      customer.RowGuid = customer.SafeRead(reader, "rowguid", _
         Guid.NewGuid())
      customer.ModifiedDate = customer.SafeRead(reader, _
         "ModifiedDate", DateTime.Now)

      Return customer
   End Function

   <Extension()> _
   Function SafeRead(Of T)(ByVal customer As Customer, _
      ByVal reader As SqlDataReader, ByVal fieldName As String, _
      ByVal defaultValue As T) As T

      Try
         Return Convert.ChangeType(reader(fieldName), _
            defaultValue.GetType())
      Catch ex As Exception
         Return defaultValue
      End Try

   End Function

   Public Class Customer
      Private _customerID AsInteger
      Public Property CustomerID() As Integer
         Get
            Return _customerID
         End Get
         Set(ByVal Value As Integer)
            _customerID = Value
         End Set
      End Property

      Private _territoryID As Integer
      Public Property TerritoryID() As Integer
         Get
            Return _territoryID
         End Get
         Set(ByVal Value As Integer)
            _territoryID = Value
         End Set
      End Property

      Private _accountNumber As String
      Public Property AccountNumber() As String
         Get
            Return _accountNumber
         End Get
         Set(ByVal Value As String)
            _accountNumber = Value
         EndSet
      End Property

      Private _customerType As String
      Public Property CustomerType() As String
         Get
            Return _customerType
         End Get
         Set(ByVal Value As String)
            _customerType = Value
         End Set
      End Property

      Private _rowGuid As Guid
      Public Property RowGuid() As Guid
         Get
            Return _rowGuid
         End Get
         Set(ByVal Value As Guid)
            _rowGuid = Value
         End Set
      End Property

      Private _modifiedDate As DateTime
      Public Property ModifiedDate() As DateTime
         Get
            Return _modifiedDate
         End Get
         Set(ByVal Value As DateTime)
            _modifiedDate = Value
         End Set
      End Property

   End Class

End Module

If you need a refresher on extension methods, LINQ, or any of the techniques in this article, you can check out many years of back articles on codeguru.com (in the VB Today column) or developer.com.

Summary

Functional construction basically is a part of LINQ to XML that lets you construct an XML document from any data with one line of code. Because XML is self-describing and text, it is highly portable and highly desirable as a standard technology. Being able to easily move to and from an XML format is also highly desirable.

About the Author

Paul Kimmel is the VB Today columnist for www.codeguru.com and has written several books on object-oriented programming and .NET. Check out his upcoming book LINQ Unleashed for C# due in July 2008. Paul Kimmel is an Application Architect for EDS. You may contact him for technology questions at pkimmel@softconcepts.com.

Lansing is having a free Day of .NET training at Lansing Community College on June 21^st. Check out the web site for details. The group likes to think of it as a poor man's TechEd (because it's free), but the content will be excellent.

Copyright © 2008 by Paul T. Kimmel. All Rights Reserved.

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This article was originally published on June 3, 2008