此範例示範如何設定 BLOB 數據、建立數據表、新增範例記錄、擷取數據列集中的記錄，然後設定 BLOB 字段的值。 IA64 不支援此範例。
若要將指標傳遞至自己的記憶體物件，取用者會建立一個存取子，以系結 BLOB 數據行的值，然後呼叫 IRowsetChange::SetData 或 IRowsetChange::InsertRow 方法。
此範例需要 AdventureWorks 範例資料庫，您可以從 Microsoft SQL Server 範例和社群專案 首頁下載。
這很重要
盡可能使用 Windows 驗證。 如果 Windows 驗證無法使用，請提示使用者在運行時間輸入其認證。 避免將認證儲存在檔案中。 如果您必須保存認證，您應該使用 Win32 加密 API 來加密認證。
程序
設定 BLOB 數據
建立 DBOBJECT 結構，描述 BLOB 資料行的存取方式。 將 DBOBJECT 結構的 dwFlag 元素設定為 STGM_READ，並將 iid 元素設定為
IID_ISequentialStream（要公開的介面）。設定DBPROPSET_ROWSET屬性群組中的屬性，以便更新數據列集。
使用 DBBINDING 結構的陣列，建立一組系結（每個數據行的其中一個）。 將 DBBINDING 結構中的 wType 元素設定為 DBTYPE_IUNKNOWN，並將 pObject 元素設定為指向您所建立的 DBOBJECT 結構。
使用結構之 DBBINDINGS 陣列中的系結資訊建立存取子。
呼叫
GetNextRows以將下一個數據列擷取到數據列集。 呼叫GetData以從數據列集讀取數據。若要設定數據，請建立包含數據的記憶體物件（以及長度指標），然後使用系結 BLOB 資料行的存取子呼叫
IRowsetChange::SetData（或IRowsetChange::InsertRow）。
範例
說明
使用 ole32.lib oleaut32.lib 編譯，並執行下列C++程式代碼清單。 此應用程式會連線到計算機的預設 SQL Server 實例。 在某些 Windows作系統上，您必須將 （localhost） 或 （local） 變更為 SQL Server 實例的名稱。 若要連線到具名實例，請將連接字串從 L“（local）” 變更為 L“（local）\\name”，其中 name 是具名實例。 根據預設，SQL Server Express 會安裝至具名實例。 請確定您的 INCLUDE 環境變數包含包含 sqlncli.h 的目錄。
程式碼
// compile with: ole32.lib oleaut32.lib
#define UNICODE
#define DBINITCONSTANTS
#define INITGID
#define OLEDBVER 0x0250 // to include correct interfaces
#include <windows.h>
#include <stdio.h>
#include <stddef.h>
#include <iostream>
#include <oledb.h>
#include <oledberr.h>
#include <SQLNCLI.h>
using namespace std;
#define SAFE_RELEASE(pIUnknown) if(pIUnknown) (pIUnknown)->Release();
HRESULT GetCommandObject(REFIID riid, IUnknown** ppIUnknown);
HRESULT CreateTable(ICommandText* pICommandText);
class CSeqStream : public ISequentialStream {
public:
// Constructors
CSeqStream();
virtual ~CSeqStream();
virtual BOOL Seek(ULONG iPos);
virtual BOOL Clear();
virtual BOOL CompareData(void* pBuffer);
virtual ULONG Length() { return m_cBufSize; };
virtual operator void* const() { return m_pBuffer; };
STDMETHODIMP_(ULONG) AddRef(void);
STDMETHODIMP_(ULONG) Release(void);
STDMETHODIMP QueryInterface(REFIID riid, LPVOID *ppv);
STDMETHODIMP Read(
/* [out] */ void __RPC_FAR *pv,
/* [in] */ ULONG cb,
/* [out] */ ULONG __RPC_FAR *pcbRead);
STDMETHODIMP Write(
/* [in] */ const void __RPC_FAR *pv,
/* [in] */ ULONG cb,
/* [out]*/ ULONG __RPC_FAR *pcbWritten);
private:
ULONG m_cRef; // reference count
void* m_pBuffer; // buffer
ULONG m_cBufSize; // buffer size
ULONG m_iPos; // current index position in the buffer
};
// class implementation
CSeqStream::CSeqStream() {
m_iPos = 0;
m_cRef = 0;
m_pBuffer = NULL;
m_cBufSize = 0;
// The constructor AddRef's
AddRef();
}
CSeqStream::~CSeqStream() {
// Shouldn't have any references left ASSERT(m_cRef == 0);
CoTaskMemFree(m_pBuffer);
}
ULONG CSeqStream::AddRef() {
return ++m_cRef;
}
ULONG CSeqStream::Release() {
// ASSERT(m_cRef);
if (--m_cRef)
return m_cRef;
delete this;
return 0;
}
HRESULT CSeqStream::QueryInterface(REFIID riid, void** ppv) {
// ASSERT(ppv);
*ppv = NULL;
if (riid == IID_IUnknown)
*ppv = this;
if (riid == IID_ISequentialStream)
*ppv = this;
if(*ppv) {
((IUnknown*)*ppv)->AddRef();
return S_OK;
}
return E_NOINTERFACE;
}
BOOL CSeqStream::Seek(ULONG iPos) {
// Make sure the desired position is within the buffer
// ASSERT(iPos == 0 || iPos < m_cBufSize);
// Reset the current buffer position
m_iPos = iPos;
return TRUE;
}
BOOL CSeqStream::Clear() {
// Frees the buffer
m_iPos = 0;
m_cBufSize = 0;
CoTaskMemFree(m_pBuffer);
m_pBuffer = NULL;
return TRUE;
}
BOOL CSeqStream::CompareData(void* pBuffer) {
// ASSERT(pBuffer);
// Quick and easy way to compare user buffer with the stream
return memcmp(pBuffer, m_pBuffer, m_cBufSize) == 0;
}
HRESULT CSeqStream::Read(void *pv, ULONG cb, ULONG* pcbRead) {
// Parameter checking
if (pcbRead)
*pcbRead = 0;
if (!pv)
return STG_E_INVALIDPOINTER;
if (cb == 0)
return S_OK;
// Actual code
ULONG cBytesLeft = m_cBufSize - m_iPos;
ULONG cBytesRead = cb > cBytesLeft ? cBytesLeft : cb;
// if no more bytes to retrieve return
if (cBytesLeft == 0)
return S_FALSE;
// Copy to users buffer the number of bytes requested or remaining
memcpy(pv, (void*)((BYTE*)m_pBuffer + m_iPos), cBytesRead);
m_iPos += cBytesRead;
if (pcbRead)
*pcbRead = cBytesRead;
if (cb != cBytesRead)
return S_FALSE;
return S_OK;
}
HRESULT CSeqStream::Write(const void *pv, ULONG cb, ULONG* pcbWritten) {
// Parameter checking
if (!pv)
return STG_E_INVALIDPOINTER;
if (pcbWritten)
*pcbWritten = 0;
if (cb == 0)
return S_OK;
// Enlarge the current buffer
m_cBufSize += cb;
// Need to append to the end of the stream
m_pBuffer = CoTaskMemRealloc(m_pBuffer, m_cBufSize);
memcpy((void*)((BYTE*)m_pBuffer + m_iPos), pv, cb);
// m_iPos += cb;
if (pcbWritten)
*pcbWritten = cb;
return S_OK;
}
int main() {
CoInitialize(NULL);
DBOBJECT ObjectStruct;
ObjectStruct.dwFlags = STGM_READ;
ObjectStruct.iid = IID_ISequentialStream;
struct BLOBDATA {
DBSTATUS dwStatus;
DBLENGTH dwLength;
ISequentialStream* pISeqStream;
};
BLOBDATA BLOBGetData;
BLOBDATA BLOBSetData;
const ULONG cBindings = 1;
DBBINDING rgBindings[cBindings];
HRESULT hr = S_OK;
IAccessor* pIAccessor = NULL;
ICommandText* pICommandText = NULL;
ICommandProperties* pICommandProperties = NULL;
IRowsetChange* pIRowsetChange = NULL;
IRowset* pIRowset = NULL;
CSeqStream* pMySeqStream = NULL;
DBCOUNTITEM cRowsObtained = 0;
HACCESSOR hAccessor = DB_NULL_HACCESSOR;
DBBINDSTATUS rgBindStatus[cBindings];
HROW* rghRows = NULL;
const ULONG cPropSets = 1;
DBPROPSET rgPropSets[cPropSets];
const ULONG cProperties = 1;
DBPROP rgProperties[cProperties];
const ULONG cBytes = 10;
BYTE pBuffer[cBytes];
ULONG cBytesRead = 0;
BYTE pReadData[cBytes]; // read BLOB data in this array
memset(pReadData, 0xAA, cBytes);
BYTE pWriteData[cBytes]; // write BLOB data from this array
memset(pWriteData, 'D', cBytes);
// Get Command object
hr = GetCommandObject(IID_ICommandText, (IUnknown**)&pICommandText);
if (FAILED(hr)) {
printf("Failed to get ICommandText interface.\n");
// Release any references and return.
goto Exit;
}
// Create table with image column and index
hr = CreateTable(pICommandText);
if (FAILED(hr)) {
printf("Failed to create table.\n");
// Release any references and return.
goto Exit;
}
// Set the DBPROPSET structure. It is used to pass an array
// of DBPROP structures to SetProperties().
rgPropSets[0].guidPropertySet = DBPROPSET_ROWSET;
rgPropSets[0].cProperties = cProperties;
rgPropSets[0].rgProperties = rgProperties;
// Now set properties in the property group (DBPROPSET_ROWSET)
rgPropSets[0].rgProperties[0].dwPropertyID = DBPROP_UPDATABILITY;
rgPropSets[0].rgProperties[0].dwOptions = DBPROPOPTIONS_REQUIRED;
rgPropSets[0].rgProperties[0].dwStatus = DBPROPSTATUS_OK;
rgPropSets[0].rgProperties[0].colid = DB_NULLID;
rgPropSets[0].rgProperties[0].vValue.vt = VT_I4;
V_I4(&rgPropSets[0].rgProperties[0].vValue) = DBPROPVAL_UP_CHANGE;
// Set the rowset properties
hr = pICommandText->QueryInterface(IID_ICommandProperties,
(void **)&pICommandProperties);
if (FAILED(hr)) {
printf("Failed to get ICommandProperties to set rowset properties.\n");
// Release any references and return.
goto Exit;
}
hr = pICommandProperties->SetProperties(cPropSets, rgPropSets);
if (FAILED(hr)) {
printf("Execute failed to set rowset properties.\n");
// Release any references and return.
goto Exit;
}
// Execute a command (SELECT * FROM TestISeqStream)
hr = pICommandText->SetCommandText(DBGUID_DBSQL, L"SELECT * FROM TestISeqStream");
if (FAILED(hr)) {
printf("Failed to set command text SELECT * FROM.\n");
// Release any references and return.
goto Exit;
}
hr = pICommandText->Execute(NULL,
IID_IRowsetChange,
NULL,
NULL,
(IUnknown**)&pIRowsetChange);
if (FAILED(hr)) {
printf("Failed to execute the command SELECT * FROM.\n");
// Release any references and return.
goto Exit;
}
// Fill the DBBINDINGS array.
rgBindings[0].iOrdinal = 2; // ordinal position
rgBindings[0].obValue = offsetof(BLOBDATA, pISeqStream);
rgBindings[0].obLength = offsetof(BLOBDATA, dwLength);
rgBindings[0].obStatus = offsetof(BLOBDATA, dwStatus);
rgBindings[0].pTypeInfo = NULL;
rgBindings[0].pObject = &ObjectStruct;
rgBindings[0].pBindExt = NULL;
rgBindings[0].dwPart = DBPART_VALUE | DBPART_STATUS | DBPART_LENGTH;
rgBindings[0].dwMemOwner = DBMEMOWNER_CLIENTOWNED;
rgBindings[0].eParamIO = DBPARAMIO_NOTPARAM;
rgBindings[0].cbMaxLen = 0;
rgBindings[0].dwFlags = 0;
rgBindings[0].wType = DBTYPE_IUNKNOWN;
rgBindings[0].bPrecision = 0;
rgBindings[0].bScale = 0;
// Create an accessor using the binding information.
hr = pIRowsetChange->QueryInterface(IID_IAccessor, (void**)&pIAccessor);
if (FAILED(hr)) {
printf("Failed to get IAccessor interface.\n");
// Release any references and return.
goto Exit;
}
hr = pIAccessor->CreateAccessor(DBACCESSOR_ROWDATA,
cBindings,
rgBindings,
sizeof(BLOBDATA),
&hAccessor,
rgBindStatus);
if (FAILED(hr)) {
printf("Failed to create an accessor.\n");
// Release any references and return.
goto Exit;
}
// get the first row.
hr = pIRowsetChange->QueryInterface(IID_IRowset, (void **)&pIRowset);
if (FAILED(hr)) {
printf("Failed to get IRowset interface.\n");
// Release any references and return.
goto Exit;
}
hr = pIRowset->GetNextRows(NULL, 0, 1, &cRowsObtained, &rghRows);
hr = pIRowset->GetData(rghRows[0], hAccessor, &BLOBGetData);
// Verify the retrieved data, only if data is not null.
if (BLOBGetData.dwStatus == DBSTATUS_S_ISNULL) {
// Process null data
printf("Provider returned a null value.\n");
}
else if(BLOBGetData.dwStatus == DBSTATUS_S_OK) {
// Provider returned a nonNULL value
BLOBGetData.pISeqStream->Read( pBuffer, cBytes, &cBytesRead);
if (memcmp(pBuffer, pReadData, cBytes) != 0) {
// cleanup
}
SAFE_RELEASE(BLOBGetData.pISeqStream);
}
// Set up data for SetData.
pMySeqStream = new CSeqStream();
// Put data into ISequentialStream object for the provider to write.
pMySeqStream->Write(pWriteData, cBytes, NULL);
BLOBSetData.pISeqStream = (ISequentialStream*)pMySeqStream;
BLOBSetData.dwStatus = DBSTATUS_S_OK;
BLOBSetData.dwLength = pMySeqStream->Length();
// Set the data.
hr = pIRowsetChange->SetData(rghRows[0], hAccessor, &BLOBSetData);
if (FAILED(hr)) {
printf("Failed to set data.\n");
// Release any references and return.
goto Exit;
}
hr = pIAccessor->ReleaseAccessor(hAccessor, NULL);
if (FAILED(hr)) {
printf("Failed to release accessor.\n");
// Release any references and return.
goto Exit;
}
hr = pIRowset->ReleaseRows(cRowsObtained, rghRows, NULL, NULL, NULL);
if (FAILED(hr)) {
printf("Failed to release rows.\n");
// Release any references and return.
goto Exit;
}
Exit:
// Release all allocated memory and release interface pointers.
CoUninitialize();
}
HRESULT GetCommandObject(REFIID riid, IUnknown** ppIUnknown) {
HRESULT hr = S_OK;
// Local interface pointers, until a connection is made.
IDBInitialize* pIDBInitialize = NULL;
IDBProperties* pIDBProperties = NULL;
IDBCreateSession* pIDBCreateSession = NULL;
IDBCreateCommand* pIDBCreateCommand = NULL;
const ULONG cPropSets = 1;
DBPROPSET rgPropSets[cPropSets];
const ULONG cProperties = 4;
DBPROP rgProperties[cProperties];
// Initialize property values needed to establish connection.
for ( ULONG i = 0 ; i < 4 ; i++ )
VariantInit(&rgProperties[i].vValue);
// Server name.
rgProperties[0].dwPropertyID = DBPROP_INIT_DATASOURCE;
rgProperties[0].vValue.vt = VT_BSTR;
rgProperties[0].vValue.bstrVal = SysAllocString(L"(local)");
rgProperties[0].dwOptions = DBPROPOPTIONS_REQUIRED;
rgProperties[0].colid = DB_NULLID;
// Database.
rgProperties[1].dwPropertyID = DBPROP_INIT_CATALOG;
rgProperties[1].vValue.vt = VT_BSTR;
rgProperties[1].vValue.bstrVal = SysAllocString(L"AdventureWorks");
rgProperties[1].dwOptions = DBPROPOPTIONS_REQUIRED;
rgProperties[1].colid = DB_NULLID;
rgProperties[2].dwPropertyID = DBPROP_AUTH_INTEGRATED;
rgProperties[2].vValue.vt = VT_BSTR;
rgProperties[2].vValue.bstrVal = SysAllocString(L"SSPI");
rgProperties[2].dwOptions = DBPROPOPTIONS_REQUIRED;
rgProperties[2].colid = DB_NULLID;
// Properties are now set. Next, construct DBPROPSET structure (rgInitPropSet) used to pass an
// array of DBPROP structures (InitProperties) to the SetProperties method.
rgPropSets[0].guidPropertySet = DBPROPSET_DBINIT;
rgPropSets[0].cProperties = cProperties;
rgPropSets[0].rgProperties = rgProperties;
// Get the IDBInitialize interface.
hr = CoCreateInstance(CLSID_SQLNCLI11,
NULL,
CLSCTX_INPROC_SERVER,
IID_IDBInitialize,
(void**)&pIDBInitialize);
if (FAILED(hr)) {
printf("Failed to get IDBInitialize interface.\n");
// Release any references and return.
goto Exit;
}
// Set initialization properties.
hr = pIDBInitialize->QueryInterface(IID_IDBProperties, (void **)&pIDBProperties);
if (FAILED(hr)) {
printf("Failed to get IDBProperties interface.\n");
// Release any references and return.
goto Exit;
}
hr = pIDBProperties->SetProperties(cPropSets, rgPropSets);
if (FAILED(hr)) {
printf("Failed to set properties for DBPROPSET_DBINIT.\n");
// Release any references and return.
goto Exit;
}
hr = pIDBInitialize->Initialize();
if (FAILED(hr)) {
printf("Failed to initialize.\n");
// Release any references and return.
goto Exit;
}
// Create a session object.
hr = pIDBInitialize->QueryInterface( IID_IDBCreateSession,
(void **)&pIDBCreateSession);
if (FAILED(hr)) {
printf("Failed to get pIDBCreateSession interface.\n");
// Release any references and return.
goto Exit;
}
hr = pIDBCreateSession->CreateSession( NULL, IID_IDBCreateCommand, (IUnknown**)&pIDBCreateCommand);
if (FAILED(hr)) {
printf("Failed to create session object.\n");
// Release any references and return.
goto Exit;
}
// Get CommandText object
hr = pIDBCreateCommand->CreateCommand( NULL, riid, (IUnknown**)ppIUnknown);
if (FAILED(hr)) {
printf("Failed to create CommandText object.\n");
// Release any references and return.
goto Exit;
}
return hr;
Exit:
// Free up all allocated memory and release interface pointers.
return hr;
}
HRESULT CreateTable(ICommandText* pICommandText) {
HRESULT hr = S_OK;
// drop the table "TestISeqStream" if the table exists.
hr = pICommandText->SetCommandText( DBGUID_DBSQL, L"if object_id('TestISeqStream') is not null drop table TestISeqStream");
if (FAILED(hr)) {
printf("Failed to set command text DROP TABLE.\n");
// Release any references and return.
goto Exit;
}
hr = pICommandText->Execute(NULL, IID_NULL, NULL, NULL, NULL);
if (FAILED(hr)) {
printf("Failed to drop the table.\n");
// Release any references and return.
goto Exit;
}
// Create a new table.
hr = pICommandText->SetCommandText(DBGUID_DBSQL,
L"CREATE TABLE TestISeqStream (col1 int,col2 image)");
if (FAILED(hr)) {
printf("Failed to set command text CREATE TABLE.\n");
// Release any references and return.
goto Exit;
}
hr = pICommandText->Execute(NULL, IID_NULL, NULL, NULL, NULL);
if (FAILED(hr)) {
printf("Failed to create table.\n");
// Release any references and return.
goto Exit;
}
// Insert one row into table.
hr = pICommandText->SetCommandText(DBGUID_DBSQL,
L"INSERT INTO TestISeqStream(col1,col2) VALUES (1,0xAAAAAAAAAAAAAAAAA)");
if (FAILED(hr)) {
printf("Failed to set command text INSERT INTO.\n");
// Release any references and return.
goto Exit;
}
hr = pICommandText->Execute(NULL, IID_NULL, NULL, NULL, NULL);
if (FAILED(hr)) {
printf("Failed to insert record in the table.\n");
// Release any references and return.
goto Exit;
}
Exit:
// Release all allocated memory and release interface pointers.
return hr;
}