您可以使用 Win32 將資料讀取和寫入 FILESTREAM BLOB。 需要下列步驟：
讀取 FILESTREAM 檔案路徑。
讀取目前的交易內容。
取得 Win32 句柄，並使用句柄將數據讀取和寫入 FILESTREAM BLOB。
備註
本主題中的範例需要在 建立 FILESTREAM-Enabled 資料庫 和 建立用於儲存 FILESTREAM 資料的資料表 中創建 FILESTREAM 資料庫和資料表。
用於處理 FILESTREAM 資料的函式
當您使用 FILESTREAM 來儲存二進位大型物件 （BLOB） 資料時，您可以使用 Win32 API 來處理檔案。 為了支援在 Win32 應用程式中使用 FILESTREAM BLOB 數據，SQL Server 提供下列函式和 API：
PathName 會將路徑當做令牌傳回至 BLOB。 應用程式會使用此令牌來取得 Win32 句柄，並在 BLOB 數據上運作。
當包含 FILESTREAM 數據的資料庫屬於 AlwaysOn 可用性群組時，PathName 函式會傳回虛擬網路名稱 （VNN） 而不是計算機名稱。
GET_FILESTREAM_TRANSACTION_CONTEXT（） 會傳回代表會話目前交易的令牌。 應用程式會使用此令牌將 FILESTREAM 檔案系統串流作業系結至交易。
OpenSqlFilestream API 會取得 Win32 文件控制代碼。 應用程式會使用 句柄來串流 FILESTREAM 數據，然後可以將句柄傳遞至下列 Win32 API： ReadFile、 WriteFile、 TransmitFile、 SetFilePointer、 SetEndOfFile 或 FlushFileBuffers。 如果應用程式使用 句柄呼叫任何其他 API，則會傳回ERROR_ACCESS_DENIED錯誤。 應用程式應該使用 CloseHandle 關閉句柄。
所有 FILESTREAM 數據容器存取都會在 SQL Server 交易中執行。 Transact-SQL 語句可以在相同的交易中執行，以維持 SQL 數據和 FILESTREAM 數據之間的一致性。
存取 FILESTREAM 數據的步驟
讀取 FILESTREAM 檔案路徑
FILESTREAM 數據表中的每個儲存格都有與其相關聯的檔案路徑。 若要讀取路徑，請在 Transact-SQL 語句中使用 varbinary(max) 欄的 PathName 屬性。 下列範例示範如何讀取數據行的 varbinary(max) 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。 下列範例示範如何開始交易並讀取目前的交易內容。
DECLARE @txContext varbinary(max)
BEGIN TRANSACTION
SELECT @txContext = GET_FILESTREAM_TRANSACTION_CONTEXT()
PRINT @txContext
COMMIT
取得 Win32 檔控制碼
若要取得 Win32 檔案句柄，請呼叫 OpenSqlFilestream API。 此 API 會從 sqlncli.dll 檔案導出。 傳回的句柄可以傳遞至下列任何 Win32 API： ReadFile、 WriteFile、 TransmitFile、 SetFilePointer、 SetEndOfFile 或 FlushFileBuffers。 下列範例示範如何取得 Win32 檔案句柄，並用它來讀取和寫入 FILESTREAM BLOB 的數據。
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 <sqlncli.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做法
當您設計和實作使用 FILESTREAM 的應用程式時，請考慮下列指導方針：
使用 NULL 而非 0x 來代表非初始化的 FILESTREAM 數據行。 0x 值會導致建立檔案，而 NULL 則不會。
避免在包含非 Null FILESTREAM 欄的資料表中進行插入和刪除操作。 插入和刪除作業可以修改用於垃圾收集的 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，請使用 NEWSEQUENTIALID（） 而不是 NEWID（）。 NEWSEQUENTIALID（） 在這些應用程式中的 GUID 產生效能優於 NEWID（）。
FILESTREAM API是專為 Win32 串流存取數據所設計。 避免使用 Transact-SQL 讀取或寫入大於 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 數據，請在嘗試從 Win32 開啟 FILESTREAM BLOB 之前，先確定已取用所有 BLOB 數據。 無法取用所有 Transact-SQL 數據，可能會導致任何後續的 FILESTREAM 開啟或關閉作業失敗。
請避免 Transact-SQL 語句，這些語句會更新、附加或前置至 FILESTREAM BLOB。 這會導致 BLOB 數據被匯入到 tempdb 資料庫，然後還原到新的實體文件。
避免將小型 BLOB 更新附加至 FILESTREAM BLOB。 每次附加操作都會使基礎的 FILESTREAM 檔案被複製。 如果應用程式必須追加小型 BLOB，請將 BLOB 寫入資料行
varbinary(max)，然後在 BLOB 的數目達到預先決定的限制時，對 FILESTREAM BLOB 執行單一寫入作業。避免擷取應用程式中大量 BLOB 檔案的數據長度。 這是耗時的作業，因為大小不會儲存在 SQL Server 資料庫引擎中。 如果您需要判斷 BLOB 檔案的長度，在檔案關閉時請使用 Transact-SQL DATALENGTH() 函式來判斷 BLOB 的大小。 DATALENGTH（） 不會開啟 BLOB 檔案來判斷其大小。
如果應用程式使用消息塊 1 （SMB1） 通訊協定，則 FILESTREAM BLOB 資料應該以 60 KB 的倍數讀取，以將效能優化。
另請參閱
避免與 FILESTREAM 應用程式中的資料庫作業發生衝突
使用 OpenSqlFilestream 存取 FILESTREAM 資料
二進位大型物件 (Blob) 資料 (SQL Server)
對 FILESTREAM 數據進行部分更新