ADO.NET and XML

ADO.NET and XML

XML stands for EXtensible Markup Language.XML was designed to carry data, not to display data and XML tags are not predefined,we  must define your own tags.XML is designed to be self-descriptive and XML is a W3C Recommendation.XML is a markup language that can be used to represent complicated data in a hierarchical format.The format of the generated XML document is far more readable than the ADO equivalent – the columns are represented by elements, not attributes, and there aren't a lot of unnecessary XML namespaces:

XML Parser

An XML parser is a program that extracts the data and data descriptions and reads  XML document from the XML data And it  enables  to programmatically work with an XML document without having to manually parse the file.

The format of the generated XML document is far more readable than the ADO equivalent – the columns are represented by elements, not attributes, and there aren't a lot of unnecessary XML namespaces:

A Example of  XML Document

<?xml version="1.0"> <customer type="web"> <firstName>Kamal</firstName> <lastName>Mishra</lastName> <address>Ashok nagar Delhi </address> <city>New Delhi</city> <zip>101100</zip> </customer>

We can load any well-formed XML document into a DataSet, without having to use a predefined structure (although we might lose content if the structure of the document is not basically tabular).

// Store the XML document in a string string xmlDoc = @"<?xml version='1.0'?> <books> <book> <title>xml and ado .net</title> <publisher>R4R</publisher> </book> </books>"; // Load this into a StringReader StringReader sr = new StringReader(xmlDoc); // Create a new DataSet and read in the XML DataSet ds = new DataSet(); ds.ReadXml(sr); // Display the column names and row data as a table foreach (DataColumn dc in ds.Tables[0].Columns) { Console.Write("{0,-15}", dc.ColumnName); } Console.Write("\n"); foreach (DataRow dr in ds.Tables[0].Rows) { Console.WriteLine("{0,-15}{1,-15}", dr[0], dr[1]); }

Creating a DataSet from an XML File

The DataSet object has an overloaded method named ReadXml() that enables you to read XML data from a string, stream, or file.

dataSet.ReadXml("file.xml");

ReadXml()Method

ReadXml() is used to perform the magic of locating and loading the XML file. Readxml() is  a very robust method, and used with different way depending on what objects we pass ReadXml(), it will perform different actions:

• ReadXml( XmlReader reader, XmlReadMode mode )— When we are  passing an XmlReader as the first argument, ReadXml() will read data from an XmlReader object.
• ReadXml( Stream stream, XmlReadMode Mode )—When we are passing a stream as the first argument,ReadXml() will read data from a stream.
• ReadXml( String fileName, XmlReadMode Mode )— When we are passing a filename to ReadXml(), it will retrieve XML from a file.

XmlReadMode Options for Retrieving XML

Code	Symbol
Auto	ReadXml() automatically select  XmlReadMode by examining the XML document.
ReadSchema	ReadXml() reads XML schema and loads both data and schema into DataSet.
IgnoreSchema	ReadXml()completely ignores XML schema and try  to load data into DataSet using existing DataSet schema.
InferSchema	ReadXml()ignores explicit schema information in the XML using the structure of the XML data as the schema.
DiffGram	ReadXml()will read the XML as a DiffGram, appending and merging rows as needed.
Fragment	ReadXml()will read the document as partial XML and import the data matching theDataSet schema and ignore the rest.

Serialization

Serialization is defined as a way of saving the state of an object. In Microsoft .NET, serialization  refers to the conversion of an object's values into XML.

Deserialization normally refers to the reverse process of building an object based on saved values in an XML document.

Viewing the Contents of a DataSet

The GetXml() method of the DataSet object is  used that  return  the DataSet's contents in XML form as a string. First, a table of information is retrieved from the  table in database. Then it is placed into a label Web control in a Web form in order to display it.

EXAMPLE:-

<%@ Import Namespace="System.Data" %> <%@ Import Namespace="System.Data.SqlClient" %> <HTML> <HEAD> <script language="c#" runat="server" > void Page_Load(object sender, EventArgs e) { SqlConnection conn = new SqlConnection("Data Source=compee;Initial Catalog=Emp;Integrated Security=sspi"); SqlCommand cmd = new SqlCommand("SELECT * FROM Customers", conn) SqlDataAdapter adapt= new SqlDataAdapter(cmd) DataSet dsCustomers = new DataSet() conn.Open() adapt.Fill(dsCustomers, "Customers") conn.Close() lblOutput.Text = dsCustomers.GetXml() } </script> </HEAD> <body> <form runat="server"> XML Output:<br> <asp:label id="lblOutput" runat="server"/> </form> </body> </html>

Writing a DataSet to an XML File

WriteXml().method is used to writing a dataset to an xml file.

There are three different XmlWriteModes:

Code	Description
IgnoreSchema	Writes the DataSet as XML without any additional schema information.
WriteSchema	Writes the DataSet as XML with additional schema information included as inline XSD schema.
DiffGram	Writes the DataSet as a DiffGram.

DiffGram : A DiffGram is an XML document that is used to store original and current values for the data in aDataSet.

EXAMPLE

void Page_Load(object sender, EventArgs e) { SqlConnection conn = new SqlConnection("Data Source=compee;Initial Catalog=Emp;Integrated Security=sspi"); SqlCommand cmd = new SqlCommand("SELECT * FROM Customers", conn) SqlDataAdapter adapt= new SqlDataAdapter(cmd) DataSet dsCustomers = new DataSet() conn.Open() adapt.Fill(dsCustomers, "Customers") conn.Close() dsCustomers.WriteXml(Server.MapPath("XMLFiles/MyXMLFile.xml")); }