Retrieve XML from SQL Server 2000

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Lấy XML từ SQL Server 2000 Đôi khi tôi phải kéo dữ liệu từ cơ sở dữ liệu SQL Server của tôi vào một định dạng văn bản XML. Làm thế nào để làm điều đó với SQL Server 2000? Kỹ thuật Để thực hiện nhiệm vụ này

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12.4 Retrieve XML from SQL Server 2000 Sometimes I have to pull data from my SQL Server database into an XML document format. How do I do that with SQL Server 2000? Technique To accomplish this task, you will create a Command object with the Transact-SQL SELECT statement that you want to execute. However, at the end of your SQL statement, you will add the clause FOR XML mode. The mode can be any of these that are listed: • RAW. With this mode, each of the rows that is returned in the query result is made into a generic XML element with as the identifier tag. • AUTO. Each of the rows and the columns are identified with tags for each of the elements and attributes, using the column names as identifier tags. • EXPLICIT. Here, you have to nest and create your query in a particular way. For more information on this mode, check out the SQL Server Books Online. For this example, the code will use the RAW mode and look like this: SELECT * FROM Customers FOR XML RAW To execute the SQL statement in this case, you use the method ExecuteXMLReader. When you use this method, an XMLReader is returned. You should then iterate through the elements as seen in How-To 12.2. Steps Open and run the Visual Basic .NET-Chapter 12 solution. From the main Web page, click on the hyperlink with the caption How-To 12.4: Retrieving XML from SQL Server 2000. When the page loads, you will see an example of a T-SQL statement that retrieves data from SQL Server 2000 in an XML format. Click on the button labeled Retrieve XML, and the data will be listed in the TextArea at the bottom of the form (see Figure 12.4). 1. Create a Web Form. Then place the Label, TextBox, and Button objects as seen in Figure 12.4 on the form with the properties in Table 12.8 set. Table 12.8. Label, TextBox, and Button Control Property Settings Object Property Setting
Label Text SQL To Execute TextBox ID txtSQLToExecute Text SELECT * FROM Customers FOR XML AUTO, ELEMENTS Button ID btnRetrieveXML Text Retrieve XML TextArea ID taOutput HyperLink ID hplReturnToMain NavigateURL wfrmMain.aspx 2. Add the code in Listing 12.10 to the Click event of btnRetrieveXML. Taking the SQL statement displayed in the "Technique" section, the Command object cmdCust is created, and ExecuteXMLReader is invoked. The XMLReader then iterates through each of the elements in the document, and they concatenate to a string. Last, the string is assigned to the InnerText property of taOutput, and the connection to the XMLReader object is closed. Listing 12.10 wfrmHowTo12_4.aspx.vb: Reading an XML Document Using XMLTextReader Private Sub btnRetrieveXML_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles btnRetrieveXML.Click Dim cnn As New SqlClient.SqlConnection(BuildCnnStr("(local)", "Northwind")) Dim cmdCust As SqlClient.SqlCommand = New SqlClient.SqlCommand( _ Me.txtSQLToExecute.Text, cnn) Dim xrCust As System.Xml.XmlReader Dim intAtts As Int32 Dim intCurrAtt As Int32 Dim strOut As String Try cnn.Open() xrCust = cmdCust.ExecuteXmlReader()
While xrCust.Read() intAtts = xrCust.AttributeCount If xrCust.NodeType System.Xml.XmlNodeType.XmlDeclaration Then If intAtts > 0 Then For intCurrAtt = 0 To intAtts - 1 strOut &= xrCust(intCurrAtt) & vbCrLf Next Else strOut &= xrCust.Value & vbCrLf End If End If End While Catch excp As Exception strOut &= "Following Error Occurred: " & excp.Message Finally strOut &= vbCrLf & "Done Processing " taOutput.InnerText = strOut If Not xrCust Is Nothing Then xrCust.Close() End If cnn.Close() End Try End Sub Note You have been using the BuildCnnStr() function throughout this book. You should add this function to a module or copy it from other chapters. Here is the code for the function: Function BuildCnnStr(ByVal strServer As String, ByVal strDatabase As String) As String
Dim strTemp As String strTemp = "Data Source=" & strServer & ";" strTemp &= "Initial Catalog=" & strDatabase & ";" strTemp &= "Integrated Security=SSPI" Return strTemp End Function Figure 12.4. The information displayed here was read from SQL Server in an XML format. Comments Normally, you would be taking the XML document that the command object returned and passing that on to another system that requires the data to be in XML format. The data was displayed from the XMLReader for demonstration purposes.