Присваивание больших данных

Как получить большой объем данных

Чтобы передать указатель на собственный объект хранилища, потребитель создает метод доступа, связывающие значение столбца BLOB, и вызывает метод IRowsetChange::SetData или IRowsetChange::InsertRow. Получение данных BLOB

1. Создайте структуру DBOBJECT, описывающую, каким образом должен производиться доступ к столбцу BLOB. Присвойте элементу dwFlag структуры DBOBJECT значение STGM_READ а элементу iid – значение IID_ISequentialStream (нужный интерфейс).

2. Установите свойства в группе свойств DBPROPSET_ROWSET, чтобы включить возможность обновления для набора строк.

3. Создайте набор привязок (по одной для каждого столбца) с помощью массива структур DBBINDING. Присвойте элементу wType структуры DBBINDING значение DBTYPE_IUNKNOWN, а элементу pObject указатель на созданную структуру DBOBJECT.

4. Создайте метод доступа на основе сведений о привязках в массиве структур DBBINDINGS.

5. Вызовите GetNextRows для выборки следующих строк в набор строк. Вызовите GetData для чтения данных из этого набора строк.

6. Создайте объект хранилища, содержащий данные (а также индикатор длины) и вызовите IRowsetChange::SetData (или IRowsetChange::InsertRow) с методом доступа, привязывающим столбец BLOB к набору данных.

Примеры

В этом примере показано получение данных BLOB. Пример создает таблицу, добавляет образец записи, выбирает эту запись в наборе строк, а затем задает значение поля BLOB.

#define UNICODE#define DBINITCONSTANTS#define INITGID#include <windows.h>#include <stdio.h>#include <stddef.h>#include <iostream.h>#include <oledb.h>#include <oledberr.h>#include <sqlncli.h>#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);protected:    //Dataprivate:    ULONG       m_cRef;         // reference count    void*       m_pBuffer;      // buffer    ULONG       m_cBufSize;     // buffer size    ULONG       m_iPos;         // current index position in the buffer};//class implementationCSeqStream::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(void){    return ++m_cRef;}ULONG    CSeqStream::Release(void){//    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_s(pv, sizeof(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_s((void*)((BYTE*)m_pBuffer + m_iPos), sizeof((void*)((BYTE*)m_pBuffer + m_iPos)), pv, cb);    // m_iPos += cb;    if(pcbWritten)        *pcbWritten = cb;    return S_OK;}//...........................................................void main(){    CoInitialize(NULL);    DBOBJECT ObjectStruct;    ObjectStruct.dwFlags = STGM_READ;    ObjectStruct.iid     = IID_ISequentialStream;    struct BLOBDATA    {        DBSTATUS            dwStatus;           DWORD               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;    ULONG 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 the Command object.    hr = GetCommandObject(IID_ICommandText,                           (IUnknown**)&pICommandText);    if (FAILED(hr))    {        cout << "Failed to get ICommandText interface.\n";        // Release any references and return.        goto Exit;    } //end if    // Create table with image column and index.    hr = CreateTable(pICommandText);    if (FAILED(hr))    {        cout << "Failed to create table.\n";        // Release any references and return.        goto Exit;    } //end if        /*    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))    {        cout << "Failed to get ICommandProperties to set rowset properties.\n";        // Release any references and return.        goto Exit;    } //end if    hr = pICommandProperties->SetProperties(cPropSets, rgPropSets);    if (FAILED(hr))    {        cout << "Execute failed to set rowset properties.\n";        // Release any references and return.        goto Exit;    } //end if        // Execute a command (SELECT * FROM TestISeqStream).    hr = pICommandText->SetCommandText(DBGUID_DBSQL,                                       L"SELECT * FROM TestISeqStream");    if (FAILED(hr))    {        cout << "Failed to set command text SELECT * FROM.\n";        // Release any references and return.        goto Exit;    } //end if    hr = pICommandText->Execute(NULL, IID_IRowsetChange, NULL, NULL,                                (IUnknown**)&pIRowsetChange);    if (FAILED(hr))    {        cout << "Failed to execute the command SELECT * FROM.\n";        // Release any references and return.        goto Exit;    } //end if    // 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))    {        cout << "Failed to get IAccessor interface.\n";        // Release any references and return.        goto Exit;    } //end if    hr = pIAccessor->CreateAccessor(DBACCESSOR_ROWDATA,                                    cBindings,                                    rgBindings,                                     sizeof(BLOBDATA),                                    &hAccessor,                                    rgBindStatus);    if (FAILED(hr))    {        cout << "Failed to create an accessor.\n";        // Release any references and return.        goto Exit;    } //end if     // Now get the first row.    hr = pIRowsetChange->QueryInterface(IID_IRowset,                                         (void **)&pIRowset);    if (FAILED(hr))    {        cout << "Failed to get IRowset interface.\n";        // Release any references and return.        goto Exit;    } //end if    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.        cout << "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 in to the 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))    {        cout << "Failed to set data.\n";        // Release any references and return.        goto Exit;    } //end if    hr = pIAccessor->ReleaseAccessor(hAccessor, NULL);    if (FAILED(hr))    {        cout << "Failed to release accessor.\n";        // Release any references and return.        goto Exit;    } //end if    hr = pIRowset->ReleaseRows(cRowsObtained,                             rghRows,                             NULL,                             NULL,                             NULL);    if (FAILED(hr))    {        cout << "Failed to release rows.\n";        // Release any references and return.        goto Exit;    } //end ifExit:    // Free up all allocated memory and release interface pointers.    CoUninitialize();} //end main.//..........................................................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 the property values needed to     establish the 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"server");    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"pubs");    rgProperties[1].dwOptions = DBPROPOPTIONS_REQUIRED;    rgProperties[1].colid = DB_NULLID;    // Username (login).    rgProperties[2].dwPropertyID = DBPROP_AUTH_USERID;    rgProperties[2].vValue.vt = VT_BSTR;    rgProperties[2].vValue.bstrVal =                     SysAllocString(L"login");    rgProperties[2].dwOptions = DBPROPOPTIONS_REQUIRED;    rgProperties[2].colid = DB_NULLID;    // Password.    rgProperties[3].dwPropertyID = DBPROP_AUTH_PASSWORD;    rgProperties[3].vValue.vt = VT_BSTR;    rgProperties[3].vValue.bstrVal =                     SysAllocString(L"password");    rgProperties[3].dwOptions = DBPROPOPTIONS_REQUIRED;    rgProperties[3].colid = DB_NULLID;        /*    Now that the properties are set, construct the DBPROPSET     structure (rgInitPropSet).  The DBPROPSET structure is 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_SQLNCLI10,                             NULL,                             CLSCTX_INPROC_SERVER,                            IID_IDBInitialize,                             (void**)&pIDBInitialize);    if(FAILED(hr))    {        cout << "Failed to get IDBInitialize interface.\n";        // Release any references and return.        goto Exit;    } //end if    // Set initialization properties.    hr = pIDBInitialize->QueryInterface(IID_IDBProperties,                                        (void **)&pIDBProperties);    if(FAILED(hr))    {        cout << "Failed to get IDBProperties interface.\n";        // Release any references and return.        goto Exit;    } //end if    hr = pIDBProperties->SetProperties(cPropSets, rgPropSets);     if(FAILED(hr))    {        cout << "Failed to set properties for DBPROPSET_DBINIT.\n";        // Release any references and return.        goto Exit;    } //end if     hr = pIDBInitialize->Initialize();      if(FAILED(hr))    {        cout << "Failed to initialize.\n";        // Release any references and return.        goto Exit;    } // end if    //Create a session object.      hr = pIDBInitialize->QueryInterface(                                IID_IDBCreateSession,                                (void **)&pIDBCreateSession);       if(FAILED(hr))    {        cout << "Failed to get pIDBCreateSession interface.\n";        // Release any references and return.        goto Exit;    } // end if       hr = pIDBCreateSession->CreateSession(                                    NULL,                                     IID_IDBCreateCommand,                                    (IUnknown**)&pIDBCreateCommand);     if(FAILED(hr))    {        cout << "Failed to create session object.\n";        // Release any references and return.        goto Exit;    } // end if     // Get the CommandText object.     hr = pIDBCreateCommand->CreateCommand(                                    NULL,                                     riid,                                     (IUnknown**)ppIUnknown);     if(FAILED(hr))    {        cout << "Failed to create CommandText object.\n";        // Release any references and return.        goto Exit;    } // end if     return hr;Exit:    // Free up all allocated memory and release interface pointers.     return hr;} //end function//...............................................................HRESULT CreateTable(ICommandText* pICommandText){    HRESULT hr = S_OK;    // Drop the xisting table.    hr = pICommandText->SetCommandText(                            DBGUID_DBSQL,                            L"DROP TABLE TestISeqStream");    if(FAILED(hr))    {        cout << "Failed to set command text DROP TABLE.\n";        // Release any references and return.        goto Exit;    } //end if    hr = pICommandText->Execute(NULL, IID_NULL, NULL, NULL, NULL);    if(FAILED(hr))    {        cout << "Failed to drop the table.\n";        // Release any references and return.        goto Exit;    } // end if    // Create a new table.    hr = pICommandText->SetCommandText(DBGUID_DBSQL,         L"CREATE TABLE TestISeqStream (col1 int,col2 image)");    if(FAILED(hr))    {        cout << "Failed to set command text CREATE TABLE.\n";        // Release any references and return.        goto Exit;    } // end if    hr = pICommandText->Execute(NULL, IID_NULL, NULL, NULL, NULL);    if(FAILED(hr))    {        cout << "Failed to create new table.\n";        // Release any references and return.        goto Exit;    } // end if    // Insert one row into table.    hr = pICommandText->SetCommandText(DBGUID_DBSQL,    L"INSERT INTO TestISeqStream(col1,col2) VALUES (1,0xAAAAAAAAAAAAAAAAA)");    if(FAILED(hr))    {        cout << "Failed to set command text INSERT INTO.\n";        // Release any references and return.        goto Exit;    } // end if    hr = pICommandText->Execute(NULL, IID_NULL, NULL, NULL, NULL);    if(FAILED(hr))    {        cout << "Failed to insert record in the table.\n";        // Release any references and return.        goto Exit;    } // end if   Exit:    // Free up all allocated memory and release interface pointers.     return hr;} //end function

См. также

Основные понятия