Using an XmlDocument Object to Store an XML Document

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Bạn sử dụng một đối tượng của lớp XmlDocument để đại diện cho một tài liệu XML trong một chương trình C #. Một đối tượng XmlDocument cửa hàng các nút của các tài liệu XML trong các đối tượng của lớp XmlNode. Bạn có thể, ví dụ, dòng tải từ cơ sở dữ liệu vào một đối tượng DataSet, và sau đó tải một đại diện XML của những người hàng vào một đối tượng XmlDocument. Bảng 16,5 cho thấy một số tài sản XmlDocument...

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Nội dung Text: Using an XmlDocument Object to Store an XML Document

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 Property Type Description Attributes XmlAttributeCollection Gets the XmlAttributeCollection object that contains the attributes of the current node. BaseURI string Gets the base URI of the current node. ChildNodes XmlNodeList Gets all the child nodes of the node. DocumentElement XmlElement Gets the root XmlElement object for the XML document. DocumentType XmlDocumentType Gets the node containing the DOCTYPE declaration. FirstChild XmlNode Gets the first child of the node. HasChildNodes bool Gets a bool that indicates whether this node has any child nodes. Implementation XmlImplementation Gets the XmlImplementation object for the XML document. InnerText string Gets or sets the concatenated values of the node and all of its children. InnerXml string Gets or sets the XML that represents the children of the current node. IsReadOnly bool Gets a bool value that indicates whether the current node is read-only. LastChild XmlNode Gets the last child of the node. LocalName string Gets the local name of the node. Name string Gets the qualified name of the node. NamespaceURI string Gets the namespace URI of the node. NameTable XmlNameTable Gets the XmlNameTable object associated
Table 16.5: XmlDocument Properties Property Type Description with the XML implementation. NextSibling XmlNode Gets the node immediately following the current node. NodeType XmlNodeType Gets the type of the current node. OuterXml string Gets the XML that represents the current node and all of its children. OwnerDocument XmlDocument Gets the XmlDocument object that the current node belongs to. ParentNode XmlNode Gets the parent of the current node. Prefix string Gets or sets the namespace prefix of the current node. PreserveWhitespace bool Gets or sets a bool value that indicates whether white space is to be preserved when XML is loaded or saved. The default is false. PreviousSibling XmlNode Gets the node immediately preceding the current node. Value string Gets or sets the value of the current node. XmlResolver XmlResolver Sets the XmlResolver object to use for resolving external resources. Table 16.6: XmlDocument Methods Method Return Type Description AppendChild() XmlNode Adds the specified node to the end of child nodes. CloneNode() XmlNode Creates a duplicate of the node. CreateAttribute() XmlAttribute Creates an XmlAttribute object of the specified name. CreateCDataSection() XmlCDataSection Creates an XmlCDataSection object with the specified data. CreateComment() XmlComment Creates an XmlComment object with the specified data. CreateDocumentFragment() XmlDocumentFragment Creates an XmlDocumentFragment object with the specified data.
Table 16.6: XmlDocument Methods Method Return Type Description CreateDocumentType() XmlDocumentType Creates a new XmlDocumentType object with the specified data. CreateElement() XmlElement Overloaded. Creates an XmlElement object. CreateEntityReference() XmlEntityReference Creates an XmlEntityReference object with the specified name. CreateNavigator() XpathNavigator Creates an XpathNavigator object that you can use to navigate the XML document. CreateNode() XmlNode Overloaded. Creates an XmlNode object. CreateTextNode() XmlText Creates an XmlText object with the specified text. CreateWhitespace() XmlWhitespace Creates an XmlWhitespace object. CreateXmlDeclaration() XmlDeclaration Creates an XmlDeclaration object. GetElementById() XmlElement Gets the XmlElement object with the specified ID. GetElementsByTagName() XmlNodeList Overloaded. Returns an XmlNodeList object that contains a list of all descendant elements that match the specified name. GetNamespaceOfPrefix() string Looks up the closest xmlns declaration with the specified prefix that is in scope for the current node, and then returns the namespace URI. GetPrefixOfNamespace() string Looks up the closest xmlns declaration with the specified namespace URI that is in scope for the current node, and then returns the prefix. ImportNode() XmlNode Imports a node from another XML document into the current XML document. InsertAfter() XmlNode Inserts the specified node immediately after the specified
Table 16.6: XmlDocument Methods Method Return Type Description reference node. InsertBefore() XmlNode Inserts the specified node immediately before the specified reference node. Load() void Overloaded. Loads XML data into your XmlDocument object. LoadXml() void Loads the XML document from the specified string into your XmlDocument object. PrependChild() XmlNode Adds the specified node to the beginning of the child nodes. ReadNode() XmlNode Creates an XmlNode object based on the information in a specified XmlReader object. Your XmlReader must be positioned on a node or attribute. RemoveAll() void Removes all the children and attributes of the current node. RemoveChild() XmlNode Removes the specified child node. ReplaceChild() XmlNode Replaces one child node with another. Save() void Overloaded. Saves the XML document to the specified location. SelectNodes() XmlNodeList Overloaded. Selects a list of nodes matching the specified XPath expression. SelectSingleNode() XmlNode Overloaded. Selects the first XmlNode that matches the specified XPath expression. WriteContentTo() void Saves all the children of the XML document to the specified XmlWriter object. WriteTo() void Saves the XML document to the 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: ALFKI Alfreds Futterkiste Germany ANATR Ana Trujillo Emparedados y helados Mexico
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