SqlCommand.BeginExecuteXmlReader 方法

定義

命名空間:: System.Data.SqlClient

組件:: System.Data.dll

重要

部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。

啟動非同步執行由此 SqlCommand 描述的 Transact-SQL 語句或儲存程序，並將結果以 XmlReader 物件形式回傳。

多載

名稱	Description
BeginExecuteXmlReader()	啟動非同步執行由此 SqlCommand 描述的 Transact-SQL 語句或儲存程序，並將結果以 XmlReader 物件形式回傳。
BeginExecuteXmlReader(AsyncCallback, Object)	啟動非同步執行由此 SqlCommand 描述的 Transact-SQL 語句或儲存程序，並以回調程序回傳結果 XmlReader 為物件。

BeginExecuteXmlReader()

來源:: System.Data.SqlClient.notsupported.cs

啟動非同步執行由此 SqlCommand 描述的 Transact-SQL 語句或儲存程序，並將結果以 XmlReader 物件形式回傳。

public:
 IAsyncResult ^ BeginExecuteXmlReader();

public IAsyncResult BeginExecuteXmlReader();

member this.BeginExecuteXmlReader : unit -> IAsyncResult

Public Function BeginExecuteXmlReader () As IAsyncResult

傳回

IAsyncResult

可用 IAsyncResult 來輪詢或等待結果，或兩者兼用;此值在呼叫 EndExecuteXmlReader時也需用，該值回傳單一 XML 值。

例外狀況

InvalidCastException

當設定為 Stream時，會使用除 Binary 或 VarBinary 以外的。Value SqlDbType 欲了解更多串流資訊，請參閱 SqlClient 串流支援。

-或-

SqlDbType除了 Char、NChar、NVarChar、VarChar 或 Xml，當 Value 設定為 TextReader時，會使用其他 Char、NChar、NVarChar、VarChar 或 Xml。

-或-

當設定為 XmlReader時，會使用 Xml 以外的。Value SqlDbType

SqlException

執行指令文字時發生的任何錯誤。

-或-

串流操作中發生了一次超時。欲了解更多串流資訊，請參閱 SqlClient 串流支援。

InvalidOperationException

名稱/值對「Asynchronous Processing=true」未包含在定義此 SqlCommand連線的連接字串中。

-或-

在 SqlConnection 串流操作中關閉或掉落。欲了解更多串流資訊，請參閱 SqlClient 串流支援。

IOException

在串流操作中，物件或發生Stream XmlReader TextReader錯誤。欲了解更多串流資訊，請參閱 SqlClient 串流支援。

ObjectDisposedException

Stream該， XmlReader 或TextReader物件在串流操作中被關閉。欲了解更多串流資訊，請參閱 SqlClient 串流支援。

範例

以下主控台應用程式開始非同步擷取 XML 資料的過程。在等待結果的同時，這個簡單的應用程式會 IsCompleted 循環調查房產價值。程序完成後，程式碼會擷取 XML 並顯示其內容。

using System.Data.SqlClient;
using System.Xml;

class Class1
{
    static void Main()
    {
        // This example is not terribly effective, but it proves a point.
        // The WAITFOR statement simply adds enough time to prove the
        // asynchronous nature of the command.
        string commandText =
            "WAITFOR DELAY '00:00:03';" +
            "SELECT Name, ListPrice FROM Production.Product " +
            "WHERE ListPrice < 100 " +
            "FOR XML AUTO, XMLDATA";

        RunCommandAsynchronously(commandText, GetConnectionString());

        Console.WriteLine("Press ENTER to continue.");
        Console.ReadLine();
    }

    private static void RunCommandAsynchronously(
        string commandText, string connectionString)
    {
        // Given command text and connection string, asynchronously execute
        // the specified command against the connection. For this example,
        // the code displays an indicator as it is working, verifying the
        // asynchronous behavior.
        using (SqlConnection connection = new SqlConnection(connectionString))
        {
            SqlCommand command = new SqlCommand(commandText, connection);

            connection.Open();
            IAsyncResult result = command.BeginExecuteXmlReader();

            // Although it is not necessary, the following procedure
            // displays a counter in the console window, indicating that
            // the main thread is not blocked while awaiting the command
            // results.
            int count = 0;
            while (!result.IsCompleted)
            {
                Console.WriteLine("Waiting ({0})", count++);
                // Wait for 1/10 second, so the counter
                // does not consume all available resources
                // on the main thread.
                System.Threading.Thread.Sleep(100);
            }

            XmlReader reader = command.EndExecuteXmlReader(result);
            DisplayProductInfo(reader);
        }
    }

    private static void DisplayProductInfo(XmlReader reader)
    {
        // Display the data within the reader.
        while (reader.Read())
        {
            // Skip past items that are not from the correct table.
            if (reader.LocalName.ToString() == "Production.Product")
            {
                Console.WriteLine("{0}: {1:C}",
                    reader["Name"], Convert.ToSingle(reader["ListPrice"]));
            }
        }
    }

    private static string GetConnectionString()
    {
        // To avoid storing the connection string in your code,
        // you can retrieve it from a configuration file.

        // If you have not included "Asynchronous Processing=true" in the
        // connection string, the command is not able
        // to execute asynchronously.
        return "Data Source=(local);Integrated Security=true;" +
            "Initial Catalog=AdventureWorks; Asynchronous Processing=true";
    }
}

Imports System.Data.SqlClient
Imports System.Xml

Module Module1

    Sub Main()
        ' This example is not terribly effective, but it proves a point.
        ' The WAITFOR statement simply adds enough time to prove the 
        ' asynchronous nature of the command.
        Dim commandText As String = _
         "WAITFOR DELAY '00:00:03';" & _
         "SELECT Name, ListPrice FROM Production.Product " & _
         "WHERE ListPrice < 100 " & _
         "FOR XML AUTO, XMLDATA"

        RunCommandAsynchronously(commandText, GetConnectionString())

        Console.WriteLine("Press ENTER to continue.")
        Console.ReadLine()
    End Sub

    Private Sub RunCommandAsynchronously( _
     ByVal commandText As String, ByVal connectionString As String)

        ' Given command text and connection string, asynchronously execute
        ' the specified command against the connection. For this example,
        ' the code displays an indicator as it is working, verifying the 
        ' asynchronous behavior. 
        Using connection As New SqlConnection(connectionString)
            Try
                Dim command As New SqlCommand(commandText, connection)
                connection.Open()
                Dim result As IAsyncResult = command.BeginExecuteXmlReader()

                ' Although it is not necessary, the following procedure
                ' displays a counter in the console window, indicating that 
                ' the main thread is not blocked while awaiting the command 
                ' results.
                Dim count As Integer = 0
                While Not result.IsCompleted
                    count += 1
                    Console.WriteLine("Waiting ({0})", count)
                    ' Wait for 1/10 second, so the counter
                    ' does not consume all available resources 
                    ' on the main thread.
                    Threading.Thread.Sleep(100)
                End While

                Using reader As XmlReader = command.EndExecuteXmlReader(result)
                    DisplayProductInfo(reader)
                End Using
            Catch ex As SqlException
                Console.WriteLine("Error ({0}): {1}", ex.Number, ex.Message)
            Catch ex As InvalidOperationException
                Console.WriteLine("Error: {0}", ex.Message)
            Catch ex As Exception
                ' You might want to pass these errors
                ' back out to the caller.
                Console.WriteLine("Error: {0}", ex.Message)
            End Try
        End Using
    End Sub

    Private Sub DisplayProductInfo(ByVal reader As XmlReader)
        ' Display the data within the reader.
        While reader.Read()
            ' Skip past items that are not from the correct table.
            If reader.LocalName.ToString = "Production.Product" Then
                Console.WriteLine("{0}: {1:C}", _
                 reader("Name"), CSng(reader("ListPrice")))
            End If
        End While
    End Sub

    Private Function GetConnectionString() As String
        ' To avoid storing the connection string in your code,            
        ' you can retrieve it from a configuration file. 

        ' If you have not included "Asynchronous Processing=true" in the
        ' connection string, the command is not able
        ' to execute asynchronously.
        Return "Data Source=(local);Integrated Security=true;" & _
          "Initial Catalog=AdventureWorks; Asynchronous Processing=true"
    End Function
End Module

備註

此 BeginExecuteXmlReader 方法啟動非同步執行一個 Transact-SQL 語句的過程，該語句以 XML 格式回傳資料列，讓其他任務能在該語句執行時同時執行。當敘述完成後，開發者必須呼叫該 EndExecuteXmlReader 方法以完成操作並取得指令回傳的 XML。該 BeginExecuteXmlReader 方法會立即回傳，但在程式碼執行對應 EndExecuteXmlReader 的方法呼叫之前，不能執行任何對同一 SqlCommand 物件啟動同步或非同步執行的其他呼叫。在指令執行完成前呼叫， EndExecuteXmlReader 物件會阻塞 SqlCommand 直到執行完成。

此 CommandText 屬性通常指定一個具有有效 FOR XML 子句的 Transact-SQL 語句。然而，也可以 CommandText 指定一個回傳 ntext 包含有效 XML 的資料的陳述句。

典型 BeginExecuteXmlReader 的查詢格式可如以下 C# 範例所示：

SqlCommand command = new SqlCommand("SELECT ContactID, FirstName, LastName FROM dbo.Contact FOR XML AUTO, XMLDATA", SqlConn);

此方法也可用於取得單列單欄結果集。此時若返回 EndExecuteXmlReader 多列，方法會將 XmlReader 附加於第一列的值，並捨棄其餘結果集。

多重主動結果集（MARS）功能允許多個動作共用同一連線。

請注意，指令文字與參數是同步傳送到伺服器的。若傳送大型指令或多個參數，此方法可能會在寫入時阻塞。指令發送後，方法會立即返回，無需等待伺服器回應——也就是說，讀取是非同步的。雖然指令執行是非同步的，但取值仍然是同步的。

由於此過載不支援回調程序，開發者需要利用方法返回的屬性IAsyncResult輪詢指令是否完成IsCompleted;或等待一個或多個指令完成，使用AsyncWaitHandle返回IAsyncResult的屬性。BeginExecuteXmlReader

如果您使用 ExecuteReader 或 BeginExecuteReader 存取 XML 資料，SQL Server 會以多列 2,033 字元返回任何長度超過 2,033 字元的 XML 結果。為避免此行為，請使用 ExecuteXmlReader 或 BeginExecuteXmlReader 讀取 FOR XML 查詢。

此方法忽略了該 CommandTimeout 性質。

另請參閱

適用於

BeginExecuteXmlReader(AsyncCallback, Object)

來源:: System.Data.SqlClient.notsupported.cs

啟動非同步執行由此 SqlCommand 描述的 Transact-SQL 語句或儲存程序，並以回調程序回傳結果 XmlReader 為物件。

public:
 IAsyncResult ^ BeginExecuteXmlReader(AsyncCallback ^ callback, System::Object ^ stateObject);

public IAsyncResult BeginExecuteXmlReader(AsyncCallback callback, object stateObject);

member this.BeginExecuteXmlReader : AsyncCallback * obj -> IAsyncResult

Public Function BeginExecuteXmlReader (callback As AsyncCallback, stateObject As Object) As IAsyncResult

參數

callback: AsyncCallback

當 AsyncCallback 指令執行完成時會被召喚的代理人。在 Microsoft Visual Basic 中 Pass nullNothing 表示不需要回調。

stateObject: Object

一個由使用者定義的狀態物件，傳遞給回調程序。利用プロパティ AsyncState 從回調程序中擷取此物件。

傳回

IAsyncResult

可用 IAsyncResult 來輪詢、等待結果，或兩者兼具;當呼叫時 EndExecuteXmlReader(IAsyncResult) ，這個值也會被要求，因為指令的結果會以 XML 形式回傳。

例外狀況

InvalidCastException

當設定為 Stream時，會使用除 Binary 或 VarBinary 以外的。Value SqlDbType 欲了解更多串流資訊，請參閱 SqlClient 串流支援。

-或-

SqlDbType除了 Char、NChar、NVarChar、VarChar 或 Xml，當 Value 設定為 TextReader時，會使用其他 Char、NChar、NVarChar、VarChar 或 Xml。

-或-

當設定為 XmlReader時，會使用 Xml 以外的。Value SqlDbType

SqlException

執行指令文字時發生的任何錯誤。

-或-

串流操作中發生了一次超時。欲了解更多串流資訊，請參閱 SqlClient 串流支援。

InvalidOperationException

名稱/值對「Asynchronous Processing=true」未包含在定義此 SqlCommand連線的連接字串中。

-或-

在 SqlConnection 串流操作中關閉或掉落。欲了解更多串流資訊，請參閱 SqlClient 串流支援。

IOException

在串流操作中，物件或發生Stream XmlReader TextReader錯誤。欲了解更多串流資訊，請參閱 SqlClient 串流支援。

ObjectDisposedException

Stream該， XmlReader 或TextReader物件在串流操作中被關閉。欲了解更多串流資訊，請參閱 SqlClient 串流支援。

範例

下列 Windows 應用程式示範如何使用 BeginExecuteXmlReader 方法，來執行包含數秒延遲的 Transact-SQL 陳述式 (模擬長時間執行的命令)。此範例將執行 SqlCommand 物件作為 stateObject 參數傳遞——這樣做使得從回調程序中取得 SqlCommand 物件變得簡單，程式碼便能呼叫 EndExecuteXmlReader 對應初始呼叫 BeginExecuteXmlReader的方法。

此範例展示了許多重要的技巧。這包括呼叫一個從獨立執行緒與表單互動的方法。此外，這個範例說明了你必須阻止使用者同時執行多次指令，以及如何確保表單在呼叫回調程序被呼叫前不會關閉。

若要設定此範例，請建立新的 Windows 應用程式。在表單上加上一個控制點、ListBox一個控制點，再加Button一個Label控制點（接受每個控制項的預設名稱）。在表單的類別中加入以下程式碼，並根據環境需要修改連接字串。

using System.Data.SqlClient;
using System.Xml;

namespace Microsoft.AdoDotNet.CodeSamples
{
    public partial class Form1 : Form
    {
        // Hook up the form's Load event handler and then add
        // this code to the form's class:
        // You need these delegates in order to display text from a thread
        // other than the form's thread. See the HandleCallback
        // procedure for more information.
        private delegate void DisplayInfoDelegate(string Text);
        private delegate void DisplayReaderDelegate(XmlReader reader);

        private bool isExecuting;

        // This example maintains the connection object
        // externally, so that it is available for closing.
        private SqlConnection connection;

        public Form1()
        {
            InitializeComponent();
        }

        private string GetConnectionString()
        {
            // To avoid storing the connection string in your code,
            // you can retrieve it from a configuration file.

            // If you do not include the Asynchronous Processing=true name/value pair,
            // you wo not be able to execute the command asynchronously.
            return "Data Source=(local);Integrated Security=true;" +
            "Initial Catalog=AdventureWorks; Asynchronous Processing=true";
        }

        private void DisplayStatus(string Text)
        {
            this.label1.Text = Text;
        }

        private void ClearProductInfo()
        {
            // Clear the list box.
            this.listBox1.Items.Clear();
        }

        private void DisplayProductInfo(XmlReader reader)
        {
            // Display the data within the reader.
            while (reader.Read())
            {
                // Skip past items that are not from the correct table.
                if (reader.LocalName.ToString() == "Production.Product")
                {
                    this.listBox1.Items.Add(String.Format("{0}: {1:C}",
                        reader["Name"], Convert.ToDecimal(reader["ListPrice"])));
                }
            }
            DisplayStatus("Ready");
        }

        private void Form1_FormClosing(object sender,
            System.Windows.Forms.FormClosingEventArgs e)
        {
            if (isExecuting)
            {
                MessageBox.Show(this, "Cannot close the form until " +
                    "the pending asynchronous command has completed. Please wait...");
                e.Cancel = true;
            }
        }

        private void button1_Click(object sender, System.EventArgs e)
        {
            if (isExecuting)
            {
                MessageBox.Show(this,
                    "Already executing. Please wait until the current query " +
                    "has completed.");
            }
            else
            {
                SqlCommand command = null;
                try
                {
                    ClearProductInfo();
                    DisplayStatus("Connecting...");
                    connection = new SqlConnection(GetConnectionString());

                    // To emulate a long-running query, wait for
                    // a few seconds before working with the data.
                    string commandText =
                        "WAITFOR DELAY '00:00:03';" +
                        "SELECT Name, ListPrice FROM Production.Product " +
                        "WHERE ListPrice < 100 " +
                        "FOR XML AUTO, XMLDATA";

                    command = new SqlCommand(commandText, connection);
                    connection.Open();

                    DisplayStatus("Executing...");
                    isExecuting = true;
                    // Although it is not required that you pass the
                    // SqlCommand object as the second parameter in the
                    // BeginExecuteXmlReader call, doing so makes it easier
                    // to call EndExecuteXmlReader in the callback procedure.
                    AsyncCallback callback = new AsyncCallback(HandleCallback);
                    command.BeginExecuteXmlReader(callback, command);
                }
                catch (Exception ex)
                {
                    isExecuting = false;
                    DisplayStatus(string.Format("Ready (last error: {0})", ex.Message));
                    if (connection != null)
                    {
                        connection.Close();
                    }
                }
            }
        }

        private void HandleCallback(IAsyncResult result)
        {
            try
            {
                // Retrieve the original command object, passed
                // to this procedure in the AsyncState property
                // of the IAsyncResult parameter.
                SqlCommand command = (SqlCommand)result.AsyncState;
                XmlReader reader = command.EndExecuteXmlReader(result);

                // You may not interact with the form and its contents
                // from a different thread, and this callback procedure
                // is all but guaranteed to be running from a different thread
                // than the form.

                // Instead, you must call the procedure from the form's thread.
                // One simple way to accomplish this is to call the Invoke
                // method of the form, which calls the delegate you supply
                // from the form's thread.
                DisplayReaderDelegate del = new DisplayReaderDelegate(DisplayProductInfo);
                this.Invoke(del, reader);
            }
            catch (Exception ex)
            {
                // Because you are now running code in a separate thread,
                // if you do not handle the exception here, none of your other
                // code catches the exception. Because none of
                // your code is on the call stack in this thread, there is nothing
                // higher up the stack to catch the exception if you do not
                // handle it here. You can either log the exception or
                // invoke a delegate (as in the non-error case in this
                // example) to display the error on the form. In no case
                // can you simply display the error without executing a delegate
                // as in the try block here.

                // You can create the delegate instance as you
                // invoke it, like this:
                this.Invoke(new DisplayInfoDelegate(DisplayStatus),
                String.Format("Ready(last error: {0}", ex.Message));
            }
            finally
            {
                isExecuting = false;
                if (connection != null)
                {
                    connection.Close();
                }
            }
        }

        private void Form1_Load(object sender, System.EventArgs e)
        {
            this.button1.Click += new System.EventHandler(this.button1_Click);
            this.FormClosing += new System.Windows.Forms.
                FormClosingEventHandler(this.Form1_FormClosing);
        }
    }
}

Imports System.Data.SqlClient
Imports System.Windows.Forms
Imports System.Xml

Public Class Form1
    ' Add this code to the form's class:
    ' You need these delegates in order to display text from a thread
    ' other than the form's thread. See the HandleCallback
    ' procedure for more information.
    Private Delegate Sub DisplayInfoDelegate(ByVal Text As String)
    Private Delegate Sub DisplayReaderDelegate(ByVal reader As XmlReader)

    Private isExecuting As Boolean

    ' This example maintains the connection object 
    ' externally, so that it is available for closing.
    Private connection As SqlConnection

    Private Function GetConnectionString() As String
        ' To avoid storing the connection string in your code,            
        ' you can retrieve it from a configuration file. 

        ' If you have not included "Asynchronous Processing=true" in the
        ' connection string, the command is not able
        ' to execute asynchronously.
        Return "Data Source=(local);Integrated Security=true;" & _
          "Initial Catalog=AdventureWorks; Asynchronous Processing=true"
    End Function

    Private Sub DisplayStatus(ByVal Text As String)
        Me.Label1.Text = Text
    End Sub

    Private Sub ClearProductInfo()
        ' Clear the list box.
        Me.ListBox1.Items.Clear()
    End Sub

    Private Sub DisplayProductInfo(ByVal reader As XmlReader)
        ' Display the data within the reader.
        While reader.Read()
            ' Skip past items that are not from the correct table.
            If reader.LocalName.ToString = "Production.Product" Then
                Me.ListBox1.Items.Add(String.Format("{0}: {1:C}", _
                    reader("Name"), CSng(reader("ListPrice"))))
            End If
        End While
        DisplayStatus("Ready")
    End Sub

    Private Sub Form1_FormClosing(ByVal sender As Object, _
        ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
        If isExecuting Then
            MessageBox.Show(Me, "Cannot close the form until " & _
                "the pending asynchronous command has completed. Please wait...")
            e.Cancel = True
        End If
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles Button1.Click
        If isExecuting Then
            MessageBox.Show(Me, "Already executing. Please wait until the current query " & _
                "has completed.")
        Else
            Dim command As SqlCommand
            Try
                ClearProductInfo()
                DisplayStatus("Connecting...")
                connection = New SqlConnection(GetConnectionString())
                ' To emulate a long-running query, wait for 
                ' a few seconds before working with the data.
                Dim commandText As String = _
                    "WAITFOR DELAY '00:00:03';" & _
                    "SELECT Name, ListPrice " & _
                    "FROM Production.Product WHERE ListPrice < 100 " & _
                    "FOR XML AUTO, XMLDATA"

                command = New SqlCommand(commandText, connection)
                connection.Open()

                DisplayStatus("Executing...")
                isExecuting = True
                ' Although it is not required that you pass the 
                ' SqlCommand object as the second parameter in the 
                ' BeginExecuteXmlReader call, doing so makes it easier
                ' to call EndExecuteXmlReader in the callback procedure.
                Dim callback As New AsyncCallback(AddressOf HandleCallback)
                command.BeginExecuteXmlReader(callback, command)

            Catch ex As Exception
                isExecuting = False
                DisplayStatus(String.Format("Ready (last error: {0})", ex.Message))
                If connection IsNot Nothing Then
                    connection.Close()
                End If
            End Try
        End If
    End Sub

    Private Sub HandleCallback(ByVal result As IAsyncResult)
        Try
            ' Retrieve the original command object, passed
            ' to this procedure in the AsyncState property
            ' of the IAsyncResult parameter.
            Dim command As SqlCommand = CType(result.AsyncState, SqlCommand)
            Dim reader As XmlReader = command.EndExecuteXmlReader(result)

            ' You may not interact with the form and its contents
            ' from a different thread, and this callback procedure
            ' is all but guaranteed to be running from a different thread
            ' than the form. 

            ' Instead, you must call the procedure from the form's thread.
            ' One simple way to accomplish this is to call the Invoke
            ' method of the form, which calls the delegate you supply
            ' from the form's thread. 
            Dim del As New DisplayReaderDelegate(AddressOf DisplayProductInfo)
            Me.Invoke(del, reader)

        Catch ex As Exception
            ' Because you are now running code in a separate thread, 
            ' if you do not handle the exception here, none of your other
            ' code catches the exception. Because none of 
            ' your code is on the call stack in this thread, there is nothing
            ' higher up the stack to catch the exception if you do not 
            ' handle it here. You can either log the exception or 
            ' invoke a delegate (as in the non-error case in this 
            ' example) to display the error on the form. In no case
            ' can you simply display the error without executing a delegate
            ' as in the Try block here. 

            ' You can create the delegate instance as you 
            ' invoke it, like this:
            Me.Invoke(New DisplayInfoDelegate(AddressOf DisplayStatus), _
                String.Format("Ready(last error: {0}", ex.Message))
        Finally
            isExecuting = False
            If connection IsNot Nothing Then
                connection.Close()
            End If
        End Try
    End Sub
End Class

備註

此 BeginExecuteXmlReader 方法啟動非同步執行 Transact-SQL 語句或儲存程序的過程，該程序以 XML 格式回傳列，使其他任務能在該語句執行時同時執行。當敘述完成後，開發者必須呼叫該 EndExecuteXmlReader 方法來完成操作並取得所請求的 XML 資料。該 BeginExecuteXmlReader 方法會立即回傳，但在程式碼執行對應 EndExecuteXmlReader 的方法呼叫之前，不能執行任何對同一 SqlCommand 物件啟動同步或非同步執行的其他呼叫。在指令執行完成前呼叫， EndExecuteXmlReader 物件會阻塞 SqlCommand 直到執行完成。

此 CommandText 屬性通常指定一個具有有效 FOR XML 子句的 Transact-SQL 語句。然而，也可以 CommandText 指定一個回傳包含有效 XML 的資料的陳述句。此方法也可用於取得單列單欄結果集。此時若返回 EndExecuteXmlReader 多列，方法會將 XmlReader 附加於第一列的值，並捨棄其餘結果集。

典型 BeginExecuteXmlReader 的查詢格式可如以下 C# 範例所示：

SqlCommand command = new SqlCommand("SELECT ContactID, FirstName, LastName FROM Contact FOR XML AUTO, XMLDATA", SqlConn);

此方法也可用於取得單列單欄結果集。此時若返回 EndExecuteXmlReader 多列，方法會將 XmlReader 附加於第一列的值，並捨棄其餘結果集。

多重主動結果集（MARS）功能允許多個動作共用同一連線。

這個 callback 參數讓你指定一個 AsyncCallback 代理，當敘述完成時會被呼叫。你可以在這個代表程序中撥打 EndExecuteXmlReader 該方法，或在申請表的其他任何地點。此外，你可以傳遞參數中 stateObject 的任何物件，回調程序也能利用該 AsyncState 屬性取得這些資訊。

請注意，指令文字與參數是同步傳送到伺服器的。如果傳送一個大型指令或多個參數，此方法可能會在寫入時阻塞。指令發送後，方法會立即返回，無需等待伺服器回應——也就是說，讀取是非同步的。

操作執行過程中發生的所有錯誤都會在回調程序中拋出為例外。你必須在回撥程序中處理例外，而不是在主應用程式中。關於回調程序中處理異常的更多資訊，請參見本主題中的範例。

此方法忽略了該 CommandTimeout 性質。

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SqlCommand.BeginExecuteXmlReader 方法

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BeginExecuteXmlReader()

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BeginExecuteXmlReader(AsyncCallback, Object)

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