建立 FILESTREAM 資料的用戶端應用程式

文章
08/23/2023

適用於：SQL Server

您可以使用 Win32 API 來讀取及寫入資料至 FILESTREAM BLOB。下面是必要的步驟：

讀取 FILESTREAM 檔案路徑。
讀取目前交易內容。
取得 Win32 控制代碼，並且使用此控制代碼來讀取及寫入資料至 FILESTREAM BLOB。

注意

本主題中的範例需要使用在建立啟用 FILESTREAM 的資料庫和建立儲存 FILESTREAM 資料的資料表中建立之啟用 FILESTREAM 的資料庫和資料表。

使用 FILESTREAM 資料的功能

當您使用 FILESTREAM 來儲存二進位大型物件 (BLOB) 資料時，可以使用 Win32 API 來處理檔案。為了支援在 Win32 應用程式中使用 FILESTREAM BLOB 資料，SQL Server 提供了下列函式和 API：

PathName 會將路徑當做 Token 傳給 BLOB。應用程式會使用此 Token 來取得 Win32 控制代碼，並在 BLOB 資料上運作。

當包含 FILESTREAM 資料的資料庫屬於 AlwaysOn 可用性群組時，PathName 函數就會傳回虛擬網路名稱 (VNN) 而非電腦名稱。
GET_FILESTREAM_TRANSACTION_CONTEXT() 會傳回代表工作階段之目前交易的 Token。應用程式會使用此 Token 將 FILESTREAM 檔案系統資料流作業繫結至此交易。
OpenSqlFilestream API 會取得 Win32 檔案控制代碼。應用程式會使用此控制代碼來為 FILESTREAM 資料進行資料流處理，然後將此控制代碼傳遞給下列 Win32 API：ReadFile、WriteFile、TransmitFile、SetFilePointer、SetEndOfFile 或 FlushFileBuffers。如果應用程式使用此控制代碼呼叫任何其他 API，就會傳回 ERROR_ACCESS_DENIED 錯誤。應用程式應該使用 CloseHandle來關閉此控制代碼。

所有 FILESTREAM 資料容器存取都是在 SQL Server 交易中執行。 Transact-SQL 陳述式可以在相同的交易中執行，以維護 SQL 資料與 FILESTREAM 資料之間的一致性。

存取 FILESTREAM 資料的步驟

讀取 FILESTREAM 檔案路徑

FILESTREAM 資料表中的每個資料格都具有與它相關聯的檔案路徑。若要讀取此路徑，請在 Transact-SQL 陳述式中使用 varbinary(max) 資料行的 PathName 屬性。下列範例將示範如何讀取 varbinary(max) 資料行的檔案路徑。

DECLARE @filePath VARCHAR(MAX);

SELECT @filePath = Chart.PathName()
FROM Archive.dbo.Records
WHERE SerialNumber = 3;

PRINT @filepath;

讀取交易內容

若要取得目前的交易內容，請使用 Transact-SQL GET_FILESTREAM_TRANSACTION_CONTEXT() 函式。下列範例將示範如何開始交易並讀取目前交易內容。

DECLARE @txContext VARBINARY(MAX);

BEGIN TRANSACTION;
SELECT @txContext = GET_FILESTREAM_TRANSACTION_CONTEXT();
PRINT @txContext;
COMMIT;

取得 Win32 檔案控制代碼

若要取得 Win32 檔案控制代碼，請呼叫 OpenSqlFilestream API。這個 API 是從 sqlncli.dll 檔案中匯出。傳回的控制代碼可傳遞給下列任何 Win32 API：ReadFile、WriteFile、TransmitFile、SetFilePointer、SetEndOfFile 或 FlushFileBuffers。下列範例將示範如何取得 Win32 檔案控制代碼，並用它來讀取及寫入資料至 FILESTREAM BLOB。

using System.IO;
using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;

namespace FILESTREAM
{
    class Program
    {
        static void Main(string[] args)
        {
            SqlConnection sqlConnection = new SqlConnection(
                "Integrated Security=true;server=(local)");

            SqlCommand sqlCommand = new SqlCommand();
            sqlCommand.Connection = sqlConnection;

            try
            {
                sqlConnection.Open();

                //The first task is to retrieve the file path
                //of the SQL FILESTREAM BLOB that we want to
                //access in the application.

                sqlCommand.CommandText =
                      "SELECT Chart.PathName()"
                    + " FROM Archive.dbo.Records"
                    + " WHERE SerialNumber = 3";

                String filePath = null;

                Object pathObj = sqlCommand.ExecuteScalar();
                if (DBNull.Value != pathObj)
                    filePath = (string)pathObj;
                else
                {
                    throw new System.Exception(
                        "Chart.PathName() failed"
                      + " to read the path name "
                      + " for the Chart column.");
                }

                //The next task is to obtain a transaction
                //context. All FILESTREAM BLOB operations
                //occur within a transaction context to
                //maintain data consistency.

                //All SQL FILESTREAM BLOB access must occur in 
                //a transaction. MARS-enabled connections
                //have specific rules for batch scoped transactions,
                //which the Transact-SQL BEGIN TRANSACTION statement
                //violates. To avoid this issue, client applications 
                //should use appropriate API facilities for transaction management, 
                //management, such as the SqlTransaction class.

                SqlTransaction transaction = sqlConnection.BeginTransaction("mainTranaction");
                sqlCommand.Transaction = transaction;

                sqlCommand.CommandText =
                    "SELECT GET_FILESTREAM_TRANSACTION_CONTEXT()";

                Object obj = sqlCommand.ExecuteScalar();
                byte[] txContext = (byte[])obj;

                //The next step is to obtain a handle that
                //can be passed to the Win32 FILE APIs.

                SqlFileStream sqlFileStream = new SqlFileStream(filePath, txContext, FileAccess.ReadWrite);

                byte[] buffer = new byte[512];

                int numBytes = 0;

                //Write the string, "EKG data." to the FILESTREAM BLOB.
                //In your application this string would be replaced with
                //the binary data that you want to write.

                string someData = "EKG data.";
                Encoding unicode = Encoding.GetEncoding(0);

                sqlFileStream.Write(unicode.GetBytes(someData.ToCharArray()),
                    0,
                    someData.Length);

                //Read the data from the FILESTREAM
                //BLOB.

                sqlFileStream.Seek(0L, SeekOrigin.Begin);

                numBytes = sqlFileStream.Read(buffer, 0, buffer.Length);

                string readData = unicode.GetString(buffer);

                if (numBytes != 0)
                    Console.WriteLine(readData);

                //Because reading and writing are finished, FILESTREAM 
                //must be closed. This closes the c# FileStream class, 
                //but does not necessarily close the underlying 
                //FILESTREAM handle. 
                sqlFileStream.Close();

                //The final step is to commit or roll back the read and write
                //operations that were performed on the FILESTREAM BLOB.

                sqlCommand.Transaction.Commit();
            }
            catch (System.Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }
            finally
            {
                sqlConnection.Close();
            }
            return;
        }
    }
}

Imports System.IO
Imports System 
Imports System.Collections.Generic 
Imports System.Text 
Imports System.Data 
Imports System.Data.SqlClient 
Imports System.Data.SqlTypes 

Module Module1
    Public Sub Main(ByVal args As String())
        '        Dim sqlConnection As New SqlConnection("Integrated Security=true;server=(local)")
        Dim sqlConnection As New SqlConnection("Integrated Security=true;server=kellyreyue\MSSQL1")

        Dim sqlCommand As New SqlCommand()
        sqlCommand.Connection = sqlConnection

        Try
            sqlConnection.Open()

            'The first task is to retrieve the file path 
            'of the SQL FILESTREAM BLOB that we want to 
            'access in the application. 

            sqlCommand.CommandText = "SELECT Chart.PathName()" + " FROM Archive.dbo.Records" + " WHERE SerialNumber = 3"

            Dim filePath As String = Nothing

            Dim pathObj As Object = sqlCommand.ExecuteScalar()
            If Not pathObj.Equals(DBNull.Value) Then
                filePath = DirectCast(pathObj, String)
            Else
                Throw New System.Exception("Chart.PathName() failed" + " to read the path name " + " for the Chart column.")
            End If

            'The next task is to obtain a transaction 
            'context. All FILESTREAM BLOB operations 
            'occur within a transaction context to 
            'maintain data consistency. 

            'All SQL FILESTREAM BLOB access must occur in 
            'a transaction. MARS-enabled connections 
            'have specific rules for batch scoped transactions, 
            'which the Transact-SQL BEGIN TRANSACTION statement 
            'violates. To avoid this issue, client applications 
            'should use appropriate API facilities for transaction management, 
            'management, such as the SqlTransaction class. 

            Dim transaction As SqlTransaction = sqlConnection.BeginTransaction("mainTranaction")
            sqlCommand.Transaction = transaction

            sqlCommand.CommandText = "SELECT GET_FILESTREAM_TRANSACTION_CONTEXT()"

            Dim obj As Object = sqlCommand.ExecuteScalar()
            Dim txContext As Byte() = Nothing

            Dim contextLength As UInteger

            If Not obj.Equals(DBNull.Value) Then
                txContext = DirectCast(obj, Byte())
                contextLength = txContext.Length()
            Else
                Dim message As String = "GET_FILESTREAM_TRANSACTION_CONTEXT() failed"
                Throw New System.Exception(message)
            End If

            'The next step is to obtain a handle that 
            'can be passed to the Win32 FILE APIs. 

            Dim sqlFileStream As New SqlFileStream(filePath, txContext, FileAccess.ReadWrite)

            Dim buffer As Byte() = New Byte(511) {}

            Dim numBytes As Integer = 0

            'Write the string, "EKG data." to the FILESTREAM BLOB. 
            'In your application this string would be replaced with 
            'the binary data that you want to write. 

            Dim someData As String = "EKG data."
            Dim unicode As Encoding = Encoding.GetEncoding(0)

            sqlFileStream.Write(unicode.GetBytes(someData.ToCharArray()), 0, someData.Length)

            'Read the data from the FILESTREAM 
            'BLOB. 

            sqlFileStream.Seek(0, SeekOrigin.Begin)

            numBytes = sqlFileStream.Read(buffer, 0, buffer.Length)

            Dim readData As String = unicode.GetString(buffer)

            If numBytes <> 0 Then
                Console.WriteLine(readData)
            End If

            'Because reading and writing are finished, FILESTREAM 
            'must be closed. This closes the c# FileStream class, 
            'but does not necessarily close the underlying 
            'FILESTREAM handle. 
            sqlFileStream.Close()

            'The final step is to commit or roll back the read and write 
            'operations that were performed on the FILESTREAM BLOB. 

            sqlCommand.Transaction.Commit()
        Catch ex As System.Exception
            Console.WriteLine(ex.ToString())
        Finally
            sqlConnection.Close()
        End Try
        Return
    End Sub
End Module

#include <windows.h>
#include <sql.h>
#include<sqltypes.h>
#include<sqlext.h>
#include <stdio.h>
#include <msodbcsql.h>

#define COPYBUFFERSIZE 4096

/// <summary>
///This class iterates though the ODBC error queue and prints all of the
///accumulated error messages to the console.
/// </summary>

class ODBCErrors
{
private:
    int         m_iLine;    //Source code line on which the error occurred
    SQLSMALLINT m_type;     //Type of handle on which the error occurred
    SQLHANDLE   m_handle;   //ODBC handle on which the error occurred

public:
    /// <summary>
    ///Default constructor for the ODBCErrors class
    ///</summary>

    ODBCErrors()
    {
        m_iLine  = -1;
        m_type   = 0;
        m_handle = SQL_NULL_HANDLE;
    }

    /// <summary>
    ///Constructor for the ODBCErrors class
    /// </summary>
    /// <param name="iLine">
    /// This parameter is the source code line
    /// at which the error occurred.
    ///</param>
    /// <param name="type">
    /// This parameter is the type of ODBC handle passed in
    /// the next parameter.
    ///</param>
    /// <param name="handle">
    /// This parameter is the handle on which the error occurred.
    ///</param>

    ODBCErrors(int iLine, SQLSMALLINT type, SQLHANDLE handle)
    {
        m_iLine  = iLine;
        m_type   = type;
        m_handle = handle;
    }

    ///<summary>
    /// This method iterates though the error stack for the handle passed
    /// into the constructor and displays those errors on the console.
    ///</summary>

    void Print()
    {
        SQLSMALLINT i = 0, len = 0;
        SQLINTEGER  native;
        SQLTCHAR    state[9], text[256];
        SQLRETURN   sqlReturn = SQL_SUCCESS;

        if ( m_handle == SQL_NULL_HANDLE )
        {
            wprintf_s(TEXT("The error handle is not a valid handle.\n"), m_iLine);
            return;
        }

        wprintf_s(TEXT("Error Line(%d)\n"), m_iLine);

        while( sqlReturn == SQL_SUCCESS )
        {
            len = 0;

            sqlReturn = SQLGetDiagRec(
                m_type,
                m_handle,
                ++i,
                state,
                &native,
                text,
                sizeof(text)/sizeof(SQLTCHAR),
                &len);

            if ( SQL_SUCCEEDED(sqlReturn) )
                wprintf_s(TEXT("Error(%d, %ld, %s) : %s\n"), i, native, state, text);
        }
    }
};


BOOL CopyFileToSQL(LPTSTR srcFilePath, LPTSTR dstFilePath, LPBYTE transactionToken, SQLINTEGER cbTransactionToken)
{
    BOOL bRetCode = FALSE;

    HANDLE srcHandle = INVALID_HANDLE_VALUE;
    HANDLE dstHandle = INVALID_HANDLE_VALUE;
    BYTE   buffer[COPYBUFFERSIZE] = { 0 };

    TCHAR *szErrMsgSrc   = TEXT("Error opening source file.");
    TCHAR *szErrMsgDst   = TEXT("Error opening destFile file.");
    TCHAR *szErrMsgRead  = TEXT("Error reading source file.");
    TCHAR *szErrMsgWrite = TEXT("Error writing SQL file.");

    try
    {
        if ( (srcHandle = CreateFile(
            srcFilePath,
            GENERIC_READ,
            FILE_SHARE_READ,
            NULL,
            OPEN_EXISTING,
            FILE_FLAG_SEQUENTIAL_SCAN,
            NULL)) == INVALID_HANDLE_VALUE )
            throw szErrMsgSrc;

        if ( (dstHandle =  OpenSqlFilestream(
            dstFilePath,
            Write,
            0,
            transactionToken,
            cbTransactionToken,
            0)) == INVALID_HANDLE_VALUE)
            throw szErrMsgDst;

        DWORD bytesRead = 0;
        DWORD bytesWritten = 0;

        do
        {
            if ( ReadFile(srcHandle, buffer, COPYBUFFERSIZE, &bytesRead, NULL) == 0 )
                throw szErrMsgRead;

            if (bytesRead > 0)
            {
                if ( WriteFile(dstHandle, buffer, bytesRead, &bytesWritten, NULL) == 0 )
                    throw szErrMsgWrite;
            }
        } while (bytesRead > 0);

        bRetCode = TRUE;
    }
    catch( TCHAR *szErrMsg )
    {
        wprintf_s(szErrMsg);
        bRetCode = FALSE;
    }

    if ( srcHandle != INVALID_HANDLE_VALUE )
        CloseHandle(srcHandle);

    if ( dstHandle != INVALID_HANDLE_VALUE )
        CloseHandle(dstHandle);

    return bRetCode;
}

void main()
{
    TCHAR *sqlDBQuery =
       TEXT("INSERT INTO Archive.dbo.Records(Id, SerialNumber, Chart)")
       TEXT(" OUTPUT GET_FILESTREAM_TRANSACTION_CONTEXT(), inserted.Chart.PathName()")
       TEXT("VALUES (newid (), 5, CONVERT(VARBINARY, '**Temp**'))");

    SQLCHAR transactionToken[32];
    
    SQLHANDLE henv = SQL_NULL_HANDLE;
    SQLHANDLE hdbc              = SQL_NULL_HANDLE;
    SQLHANDLE hstmt             = SQL_NULL_HANDLE;

    try
    {
        //These statements Initialize ODBC for the client application and
        //connect to the database.

        if ( SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &henv) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_ENV, henv);

        if ( SQLSetEnvAttr(henv, SQL_ATTR_ODBC_VERSION,(void*)SQL_OV_ODBC3, NULL) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_ENV, henv);

        if ( SQLAllocHandle(SQL_HANDLE_DBC, henv, &hdbc) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_ENV, henv);

        //This code assumes that the dataset name "Sql Server FILESTREAM"
        //has been previously created on the client computer system. An
        //ODBC DSN is created with the ODBC Data Source item in
        //the Windows Control Panel.

        if ( SQLConnect(hdbc, TEXT("Sql Server FILESTREAM"),
                SQL_NTS, NULL, 0, NULL, 0) <= 0 )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_DBC, hdbc);

        //FILESTREAM requires that all read and write operations occur
        //within a transaction.
        if ( SQLSetConnectAttr(hdbc,
            SQL_ATTR_AUTOCOMMIT,
            (SQLPOINTER)SQL_AUTOCOMMIT_OFF,
            SQL_IS_UINTEGER) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_DBC, hdbc);

        if ( SQLAllocHandle(SQL_HANDLE_STMT, hdbc, &hstmt) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_DBC, hdbc);

        if ( SQLExecDirect(hstmt, sqlDBQuery, SQL_NTS) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_STMT, hstmt);

        //Retrieve the transaction token.
        if ( SQLFetch(hstmt) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_STMT, hstmt);

        SQLINTEGER cbTransactionToken = sizeof(transactionToken);

        if ( SQLGetData(hstmt, 1,
            SQL_C_BINARY,
            transactionToken,
            sizeof(transactionToken),
            &cbTransactionToken) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_STMT, hstmt);

        //Retrieve the file path for the inserted record.

        TCHAR dstFilePath[1024];
        SQLINTEGER cbDstFilePath;

        if ( SQLGetData(hstmt, 2, SQL_C_TCHAR, dstFilePath, sizeof(dstFilePath), &cbDstFilePath) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_STMT, hstmt);

        if ( SQLCloseCursor(hstmt) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_STMT, hstmt);

        SQLUSMALLINT mode = SQL_ROLLBACK;

        if ( CopyFileToSQL(
            TEXT("C:\\Users\\Data\\chart1.jpg"),
            dstFilePath,
            transactionToken,
            cbTransactionToken) == TRUE )
            mode = SQL_COMMIT;

        SQLTransact(henv, hdbc, mode);
    }
    catch(ODBCErrors *pErrors)
    {
        pErrors->Print();
        delete pErrors;
    }

    if ( hstmt != SQL_NULL_HANDLE )
        SQLFreeHandle(SQL_HANDLE_STMT, hstmt);

    if ( hdbc != SQL_NULL_HANDLE )
        SQLDisconnect(hdbc);

    if ( hdbc != SQL_NULL_HANDLE )
        SQLFreeHandle(SQL_HANDLE_DBC, hdbc); 

    if ( henv != SQL_NULL_HANDLE )
        SQLFreeHandle(SQL_HANDLE_ENV, henv);
}

應用程式設計和實作的最佳作法

當您要設計和實作使用 FILESTREAM 的應用程式時，請考慮下列指導方針：
使用 NULL (而非 0x) 來表示未初始化的 FILESTREAM 資料行。 0x 值會導致系統建立檔案，而 NULL 則不會。
避免在包含非 Null FILESTREAM 資料行的資料表中進行插入和刪除作業。插入和刪除作業可能會修改用於記憶體回收的 FILESTREAM 資料表。這可能會導致應用程式的效能隨著時間降低。
在使用複寫的應用程式中，使用 NEWSEQUENTIALID() 來取代 NEWID()。就這些應用程式的 GUID 產生而言，NEWSEQUENTIALID() 的執行效能高於 NEWID()。
FILESTREAM API 是針對資料的 Win32 資料流存取所設計。請避免使用 Transact-SQL 來讀取或寫入超過 2 MB 的 FILESTREAM 二進位大型物件 (BLOB)。如果您必須從 Transact-SQL 讀取或寫入 BLOB，請在嘗試從 Win32 開啟 FILESTREAM BLOB 之前，確定已取用所有 BLOB 資料。如果無法取用所有 Transact-SQL 資料，可能會導致任何後續的 FILESTREAM 開啟或關閉作業失敗。
避免使用更新、附加或預先附加資料至 FILESTREAM BLOB 的 Transact-SQL 陳述式。這會導致 BLOB 資料多工緩衝處理到 tempdb 資料庫中，然後送回新的實體檔案。
避免將小型 BLOB 更新附加至 FILESTREAM BLOB。每次附加都會導致系統複製基礎 FILESTREAM 檔案。如果應用程式必須附加小型 BLOB，請將這些 BLOB 寫入 varbinary(max) 資料行，然後在 BLOB 的數目到達預先決定的限制時，針對 FILESTREAM BLOB 執行單一寫入作業。
避免在應用程式中擷取大量 BLOB 檔案的資料長度。這是一項耗時的作業，因為大小不會儲存在 SQL Server 資料庫引擎中。如果您必須判斷 BLOB 檔案的長度，請使用 Transact-SQL DATALENGTH() 函式來判斷 BLOB 的大小 (如果大小已關閉的話)。 DATALENGTH() 不會開啟 BLOB 檔案來判斷其大小。
如果應用程式使用 Message Block1 (SMB1) 通訊協定，您就應該以 60-KB 的倍數來讀取 FILESTREAM BLOB 資料，以便發揮最佳效能。

另請參閱

避免與 FILESTREAM 應用程式中的資料庫作業相衝突
 使用 OpenSqlFilestream 存取 FILESTREAM 資料
 二進位大型物件 (Blob) 資料 (SQL Server)
對 FILESTREAM 資料進行部分更新

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