Tài liệu Using an XmlDocument Object to Store an XML Document doc

An XmlDocument object stores the nodes of the XML document in objects of the XmlNode class.. Table 16.5 shows some of the XmlDocument properties; Table 16.6 shows some of the XmlDocument

Using an XmlDocument Object to Store an XML Document

You use an object of the XmlDocument class to represent an XML document in a C# program An XmlDocument object stores the nodes of the XML document in objects of the XmlNode class You can, for example, load rows from the database into a DataSet object, and then load an XML representation of those rows into an XmlDocument object Table 16.5 shows some of the XmlDocument properties; Table 16.6 shows some of the XmlDocument methods; and Table 16.7 shows the XmlDocument events

Table 16.5: XmlDocument Properties

that contains the attributes of the current node

XML document

declaration

has any child nodes

XML document

node and all of its children

children of the current node

current node is read-only

Table 16.5: XmlDocument Properties

with the XML implementation

current node

node and all of its children

current node belongs to

current node

whether white space is to be preserved when XML is loaded or saved The default

is false

current node

resolving external resources

Table 16.6: XmlDocument Methods

of child nodes

the specified name

object with the specified data

with the specified data

CreateDocumentFragment() XmlDocumentFragment Creates an

XmlDocumentFragment object with the specified data

Table 16.6: XmlDocument Methods

object with the specified data

XmlElement object

object with the specified name

that you can use to navigate the XML document

object

the specified text

the specified ID

XmlNodeList object that contains

a list of all descendant elements that match the specified name

declaration with the specified prefix that is in scope for the current node, and then returns the namespace URI

declaration with the specified namespace URI that is in scope for the current node, and then returns the prefix

document into the current XML document

immediately after the specified

Table 16.6: XmlDocument Methods

reference node

immediately before the specified reference node

your XmlDocument object

the specified string into your XmlDocument object

beginning of the child nodes

on the information in a specified XmlReader object Your

XmlReader must be positioned on

a node or attribute

attributes of the current node

another

document to the specified location

matching the specified XPath expression

XmlNode that matches the specified XPath expression

document to the specified XmlWriter object

specified XmlWriter object

Table 16.7: XmlDocument Events

Event Event Handler Description

NodeChanging XmlNodeChangedEventHandler Fires before a value in a node is

changed

NodeChanged XmlNodeChangedEventHandler Fires after a value in a node is

changed

NodeInserting XmlNodeChangedEventHandler Fires before a node is inserted

NodeInserted XmlNodeChangedEventHandler Fires after a node is inserted

NodeRemoving XmlNodeChangedEventHandler Fires before a node is removed

NodeRemoved XmlNodeChangedEventHandler Fires after a node is removed

Listing 16.17 shows a program that illustrates the use of an XmlDocument object This program performs the following steps:

1 Creates a DataSet object named myDataSet and fills it with the top two rows from the Customers table

2 Creates an XmlDocument object named myXmlDocument, and then loads it with the XML from myDataSet You can use the GetXml() method to return the

customer rows in myDataSet as a string containing a complete XML document You can then use the output string from GetXml() as the input to the LoadXml() method of myXmlDocument; this loads myXmlDocument with the XML

document containing the customer details

3 Displays the XML in myXmlDocument using the Save() method, passing

Console.Out to the Save() method This results in the XML document being displayed on the screen

4 Retrieves the XmlNode objects in myXmlDocument using the SelectNodes() method, and then displays the text contained in the child nodes of each XmlNode using the InnerText property You pass an XPath expression to SelectNodes() to retrieve the required nodes

5 Retrieves the XmlNode for the ANATR customer using the SelectSingleNode() method, and displays the text contained in the child nodes of this XmlNode You pass an XPath expression to SelectSingleNode() to retrieve the required node Listing 16.17: USINGXMLDOCUMENT.CS

/*

UsingXmlDocument.cs illustrates the use of an XmlDocument object

*/

using System;

using System.Data;

using System.Data.SqlClient;

using System.Xml;

class UsingXmlDocument

{

public static void Main()

{

SqlConnection mySqlConnection =

new SqlConnection(

"server=localhost;database=Northwind;uid=sa;pwd=sa"

);

SqlCommand mySqlCommand = mySqlConnection.CreateCommand(); mySqlCommand.CommandText =

"SELECT TOP 2 CustomerID, CompanyName, Country "+

"FROM Customers "+

"ORDER BY CustomerID";

SqlDataAdapter mySqlDataAdapter = new SqlDataAdapter();

mySqlDataAdapter.SelectCommand = mySqlCommand;

// step 1: create a DataSet object and fill it with the top 2 rows

// from the Customers table

DataSet myDataSet = new DataSet();

mySqlConnection.Open();

mySqlDataAdapter.Fill(myDataSet, "Customers");

mySqlConnection.Close();

// step 2: create an XmlDocument object and load it with the XML from // the DataSet; the GetXml() method returns the rows in

// myDataSet as a string containing a complete XML document; and

// the LoadXml() method loads myXmlDocument with the XML document // string returned by GetXml()

XmlDocument myXmlDocument = new XmlDocument();

myXmlDocument.LoadXml(myDataSet.GetXml());

// step 3: display the XML in myXmlDocument using the Save() method Console.WriteLine("Contents of myXmlDocument:");

myXmlDocument.Save(Console.Out);

// step 4: retrieve the XmlNode objects in myXmlDocument using the // SelectNodes() method; you pass an XPath expression to SelectNodes() Console.WriteLine("\n\nCustomers:");

foreach (XmlNode myXmlNode in

myXmlDocument.SelectNodes("/NewDataSet/Customers"))

{

Console.WriteLine("CustomerID = "+

myXmlNode.ChildNodes[0].InnerText);

Console.WriteLine("CompanyName = "+

myXmlNode.ChildNodes[1].InnerText);

Console.WriteLine("Country = "+

myXmlNode.ChildNodes[2].InnerText);

}

// step 5: retrieve the XmlNode for the ANATR customer using

// the SelectSingleNode() method; you pass an XPath

// expression to SelectSingleNode

Console.WriteLine("\nRetrieving node with CustomerID of ANATR");

XmlNode myXmlNode2 =

myXmlDocument.SelectSingleNode(

"/NewDataSet/Customers[CustomerID=\" ANATR\"]"

);

Console.WriteLine("CustomerID = "+

myXmlNode2.ChildNodes[0].InnerText);

Console.WriteLine("CompanyName = "+

myXmlNode2.ChildNodes[1].InnerText);

Console.WriteLine("Country = "+

myXmlNode2.ChildNodes[2].InnerText);

}

}

Remember, you'll need to change the connection string for your SqlConnection object to connect to your database near the start of this program

The output from this program is as follows:

Contents of myXmlDocument:

<?xml version="1.0" encoding="IBM437"?>

<NewDataSet>

<Customers>

<CustomerID>ALFKI</CustomerID>

<CompanyName>Alfreds Futterkiste</CompanyName>

<Country>Germany</Country>

</Customers>

<Customers>

<CustomerID>ANATR</CustomerID>

<CompanyName>Ana Trujillo Emparedados y helados</CompanyName>

<Country>Mexico</Country>

</Customers>

</NewDataSet>

Customers:

CustomerID = ALFKI

CompanyName = Alfreds Futterkiste

Country = Germany

CustomerID = ANATR

CompanyName = Ana Trujillo Emparedados y helados Country = Mexico

Retrieving node with CustomerID of ANATR

CustomerID = ANATR

CompanyName = Ana Trujillo Emparedados y helados Country = Mexico