CMyProviderWindowsFile
The wizard creates a class to contain one row of data; in this case, it is called CMyProviderWindowsFile. The following code for CMyProviderWindowsFile is wizard generated and lists all the files in a directory by using the WIN32_FIND_DATA structure. CMyProviderWindowsFile inherits from the WIN32_FIND_DATA structure:
/////////////////////////////////////////////////////////////////////
// MyProviderRS.H
class CMyProviderWindowsFile:
public WIN32_FIND_DATA
{
public:
BEGIN_PROVIDER_COLUMN_MAP(CMyProviderWindowsFile)
PROVIDER_COLUMN_ENTRY("FileAttributes", 1, dwFileAttributes)
PROVIDER_COLUMN_ENTRY("FileSizeHigh", 2, nFileSizeHigh)
PROVIDER_COLUMN_ENTRY("FileSizeLow", 3, nFileSizeLow)
PROVIDER_COLUMN_ENTRY_STR("FileName", 4, cFileName)
PROVIDER_COLUMN_ENTRY_STR("AltFileName", 5, cAlternateFileName)
END_PROVIDER_COLUMN_MAP()
};
CMyProviderWindowsFile is called the user record class because it also contains a map describing the columns in the provider's rowset. The provider column map contains one entry for each field in the rowset using the PROVIDER_COLUMN_ENTRY macros. The macros specify column name, ordinal, and offset to a structure entry. The provider column entries in the above code contain offsets into the WIN32_FIND_DATA structure. When the consumer calls IRowset::GetData, data is transferred in one contiguous buffer. Rather than making you do pointer arithmetic, the map allows you to specify a data member.
The CMyProviderRowset class also contains the Execute method. Execute is what actually reads the data in from the native source. The following code shows the wizard-generated Execute method. The function uses the Win32 FindFirstFile and FindNextFile APIs to retrieve information about the files in the directory and place them in instances of the CMyProviderWindowsFile class.
/////////////////////////////////////////////////////////////////////
// MyProviderRS.H
HRESULT Execute(DBPARAMS * pParams, LONG* pcRowsAffected)
{
USES_CONVERSION;
BOOL bFound = FALSE;
HANDLE hFile;
LPTSTR szDir = (m_strCommandText == _T("")) ? _T("*.*") :
OLE2T(m_strCommandText);
CMyProviderWindowsFile wf;
hFile = FindFirstFile(szDir, &wf);
if (hFile == INVALID_HANDLE_VALUE)
return DB_E_ERRORSINCOMMAND;
LONG cFiles = 1;
BOOL bMoreFiles = TRUE;
while (bMoreFiles)
{
if (!m_rgRowData.Add(wf))
return E_OUTOFMEMORY;
bMoreFiles = FindNextFile(hFile, &wf);
cFiles++;
}
FindClose(hFile);
if (pcRowsAffected != NULL)
*pcRowsAffected = cFiles;
return S_OK;
}
The directory to search is represented by m_strCommandText; this contains the text represented by the ICommandText interface in the command object. If no directory is specified, it uses the current directory.
The method creates one entry for each file (corresponding to a row) and places it in the m_rgRowData data member. The CRowsetImpl class defines the m_rgRowData data member. The data in this array represents the entire table and is used throughout the templates.