Valori di colonna SQL XML
SQL Server supporta il nuovo tipo di dati xml. Gli sviluppatori possono recuperare set di risultati che includono questo tipo usando il comportamento standard della classe SqlCommand. È possibile recuperare una colonna xml come qualsiasi colonna (in un SqlDataReader, ad esempio), ma se si vuole usare il contenuto della colonna come XML, è necessario usare un XmlReader.
Esempio
L'applicazione console seguente seleziona due righe, ciascuna contenente una colonna xml, dalla tabella Sales.Store nel database AdventureWorks per un'istanza SqlDataReader. Per ogni riga, il valore della colonna xml viene letto usando il metodo GetSqlXml di SqlDataReader. Questo valore viene archiviato in un XmlReader. Si noti che è necessario usare GetSqlXml anziché il metodo GetValue se si vuole impostare il contenuto in una variabile SqlXml. GetValue restituisce il valore della colonna xml sotto forma di stringa.
Nota
Per impostazione predefinita, il database di esempio AdventureWorks non viene installato insieme a SQL Server. Per installarlo, è sufficiente eseguire il programma di installazione di SQL Server.
// 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