Serializing a DataSet

ADO.NET is captured internally as XML. The reason for this has to do with XML being (1) self-describing, (2) an open standard, and (3) captured as text, which is easily transportable over networks like the Internet.

Because ADO.NET is stored as XML it becomes easy to send DataSets—ADO.NET objects—over the Internet, persist them in an external file, or serialize them for purposes like caching. For example, since a DataSet is serializable, it can be stored in the session cache in ASP.NET Web applications. In fact, a DataSet can be cached using either of the in-process caching mechanisms or the two out-of-process caching mechanisms. (The out-of-process session caching mechanisms are aspnet_state.exe and SQL Server.)

Serialization for session caching and returning DataSets from XML Web Services happens automatically, but to facilitate your understanding of what is occurring, I have included a short example that demonstrates how to serialize a DataSet to a memory stream. Listing 12.11 serializes the DataSet to a stream and displays the serialized version of the DataSet in a TextBox control.

Listing 12.11. Serializing a DataSet to XML

1:  Imports System.Data
2:  Imports System.Data.OleDb
3:  Imports System.Configuration
4:  Imports System.IO
5:  Imports System.Text.ASCIIEncoding
6:
7:  Public Class Form1
8:      Inherits System.Windows.Forms.Form
9:
10: [ Windows Form Designer generated code ]
11:
12:   Private Products As DataSet
13:   Private Sub Form1_Load(ByVal sender As Object, _
14:     ByVal e As System.EventArgs) Handles MyBase.Load
15:
16:     LoadDataSet()
17:     DataGrid1.DataSource = Products.Tables(0)
18:     SerializeDataSet(Products)
19:
20:   End Sub
21:
22:   Private Sub LoadDataSet()
23:     Dim Connection As OleDbConnection = _
24:       New OleDbConnection(ConfigurationSettings. _
25:         AppSettings("ConnectionString"))
26:
27:     Dim Adapter As OleDbDataAdapter = _
28:       New OleDbDataAdapter("SELECT * FROM PRODUCTS", _
29:         Connection)
30:
31:     Products = New DataSet("Products")
32:
33:     Adapter.Fill(Products)
34:   End Sub
35:
36:   Private Sub SerializeDataSet(ByVal Data As DataSet)
37:
38:     Dim Stream As MemoryStream = New MemoryStream()
39:     Products.WriteXml(Stream)
40:     Stream.Position = 0
41:     TextBox1.Text = System.Text.ASCIIEncoding. _
42:       ASCII.GetString(Stream.GetBuffer())
43:
44:   End Sub
45:
46: End Class

The first half of the listing initializes a DataSet with the data from the Products table. Lines 36 through 44 serialize the DataSet and data as XML into a MemoryStream object, which in turn is used to convert the XML to a string. MemoryStream objects return an array of bytes, so I employed the shared method System.Text.ASCIIEncoding.ASCII.GetString to convert the array of bytes to a string.

You can write the XML form of the DataSet back to a DataSet object by using DataSet.ReadXml. You also have the option of using the more verbose XmlSerializer method to serialize and deserialize serializable objects, but the member methods ReadXml and WriteXml work best for DataSet objects.