SQL-XML-Spaltenwerte
SQL Server unterstützt den xml-Datentyp. Daher können Entwickler Resultsets, die diesen Typ einschließen, mithilfe des Standardverhaltens der SqlCommand-Klasse abrufen. Eine xml-Spalte kann wie jede andere Spalte abgerufen werden (beispielsweise in eine SqlDataReader-Instanz), wenn Sie den Inhalt der Spalte jedoch als XML verwenden möchten, müssen Sie XmlReader verwenden.
Beispiel
Die folgende Konsolenanwendung ruft zwei Zeilen mit jeweils einer xml-Spalte aus der Sales.Store-Tabelle in der AdventureWorks-Datenbank ab und übermittelt sie an eine SqlDataReader-Instanz. Für jede Zeile wird der Wert der xml-Spalte mithilfe der GetSqlXml-Methode von SqlDataReader gelesen. Der Wert wird in einer XmlReader-Instanz gespeichert. Beachten Sie, dass Sie GetSqlXml anstelle der GetValue-Methode verwenden müssen, wenn Sie eine SqlXml-Variable als Inhalt festlegen möchten. GetValue gibt den Wert der xml-Spalte als Zeichenfolge zurück.
Hinweis
Beim Installieren von SQL Server wird die Beispieldatenbank AdventureWorks in der Standardeinstellung nicht installiert. Sie kann jedoch über das SQL Server-Setup installiert werden.
// Example assumes the following directives:
// using System.Data.SqlClient;
// using System.Xml;
// using System.Data.SqlTypes;
static void GetXmlData(string connectionString)
{
using (SqlConnection connection = new(connectionString))
{
connection.Open();
// The query includes two specific customers for simplicity's
// sake. A more realistic approach would use a parameter
// for the CustomerID criteria. The example selects two rows
// in order to demonstrate reading first from one row to
// another, then from one node to another within the xml column.
const string commandText =
"SELECT Demographics from Sales.Store WHERE " +
"CustomerID = 3 OR CustomerID = 4";
SqlCommand commandSales = new(commandText, connection);
SqlDataReader salesReaderData = commandSales.ExecuteReader();
// Multiple rows are returned by the SELECT, so each row
// is read and an XmlReader (an xml data type) is set to the
// value of its first (and only) column.
var countRow = 1;
while (salesReaderData.Read())
// Must use GetSqlXml here to get a SqlXml type.
// GetValue returns a string instead of SqlXml.
{
SqlXml salesXML =
salesReaderData.GetSqlXml(0);
XmlReader salesReaderXml = salesXML.CreateReader();
Console.WriteLine("-----Row " + countRow + "-----");
// Move to the root.
salesReaderXml.MoveToContent();
// We know each node type is either Element or Text.
// All elements within the root are string values.
// For this simple example, no elements are empty.
while (salesReaderXml.Read())
{
if (salesReaderXml.NodeType == XmlNodeType.Element)
{
var elementLocalName =
salesReaderXml.LocalName;
salesReaderXml.Read();
Console.WriteLine(elementLocalName + ": " +
salesReaderXml.Value);
}
}
countRow++;
}
}
}
' Example assumes the following directives:
' Imports System.Data.SqlClient
' Imports System.Xml
' Imports System.Data.SqlTypes
Private Sub GetXmlData(ByVal connectionString As String)
Using connection As SqlConnection = New SqlConnection(connectionString)
connection.Open()
'The query includes two specific customers for simplicity's
'sake. A more realistic approach would use a parameter
'for the CustomerID criteria. The example selects two rows
'in order to demonstrate reading first from one row to
'another, then from one node to another within the xml
'column.
Dim commandText As String = _
"SELECT Demographics from Sales.Store WHERE " & _
"CustomerID = 3 OR CustomerID = 4"
Dim commandSales As New SqlCommand(commandText, connection)
Dim salesReaderData As SqlDataReader = commandSales.ExecuteReader()
' Multiple rows are returned by the SELECT, so each row
' is read and an XmlReader (an xml data type) is set to the
' value of its first (and only) column.
Dim countRow As Integer = 1
While salesReaderData.Read()
' Must use GetSqlXml here to get a SqlXml type.
' GetValue returns a string instead of SqlXml.
Dim salesXML As SqlXml = _
salesReaderData.GetSqlXml(0)
Dim salesReaderXml As XmlReader = salesXML.CreateReader()
Console.WriteLine("-----Row " & countRow & "-----")
' Move to the root.
salesReaderXml.MoveToContent()
' We know each node type is either Element or Text.
' All elements within the root are string values.
' For this simple example, no elements
' are empty.
While salesReaderXml.Read()
If salesReaderXml.NodeType = XmlNodeType.Element Then
Dim elementLocalName As String = _
salesReaderXml.LocalName
salesReaderXml.Read()
Console.WriteLine(elementLocalName & ": " & _
salesReaderXml.Value)
End If
End While
countRow = countRow + 1
End While
End Using
End Sub