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Creating a DataReader

The DataTable and DataSet classes have a CreateDataReader method that returns the contents of the DataTable or the contents of the DataSet object's Tables collection as one or more read-only, forward-only result sets.

The following console application creates a DataTable instance. The example then passes the filled DataTable to a procedure that calls the CreateDataReader method, which iterates through the results contained within the DataTableReader.

Private Sub TestCreateDataReader(ByVal dt As DataTable)
  ' Given a DataTable, retrieve a DataTableReader 
  ' allowing access to all the tables's data: 
  Using reader As DataTableReader = dt.CreateDataReader()
    Do 
      If Not reader.HasRows Then
        Console.WriteLine("Empty DataTableReader")
      Else
        PrintColumns(reader)
      End If
      Console.WriteLine("========================")
    Loop While reader.NextResult()
  End Using 
End Sub 

Private Function GetCustomers() As DataTable
  ' Create sample Customers table, in order 
  ' to demonstrate the behavior of the DataTableReader. 
  Dim table As New DataTable

   ' Create two columns, ID and Name. 
  Dim idColumn As DataColumn = table.Columns.Add("ID", GetType(Integer))
  table.Columns.Add("Name", GetType(String))

  ' Set the ID column as the primary key column.
  table.PrimaryKey = New DataColumn() {idColumn}

  table.Rows.Add(New Object() {1, "Mary"})
  table.Rows.Add(New Object() {2, "Andy"})
  table.Rows.Add(New Object() {3, "Peter"})
  table.Rows.Add(New Object() {4, "Russ"})
  Return table
End Function 

Private Sub PrintColumns( _
   ByVal reader As DataTableReader)

  ' Loop through all the rows in the DataTableReader. 
  Do While reader.Read()
    For i As Integer = 0 To reader.FieldCount - 1
      Console.Write(reader(i).ToString() & " ")
    Next
    Console.WriteLine()
  Loop 
End Sub

The example displays the following output in the console window:

1 Mary
2 Andy
3 Peter
4 Russ
Show:
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