OLE DB Bulk Copy Operation Always Loads True into Bit Columns - c++

Question

I'm using the OLE DB bulk copy operation against a SQL Server database but I'm having trouble while loading data into bit columns - they are always populated with true!
I created a simple reproduction program from Microsoft's sample code with the snippet that I adjusted below. My program includes a little SQL script to create the destination table. I had to download and install the x64 version of the SQL Server OLE DB driver to build this.
// Set up custom bindings.
oneBinding.dwPart = DBPART_VALUE | DBPART_LENGTH | DBPART_STATUS;
oneBinding.iOrdinal = 1;
oneBinding.pTypeInfo = NULL;
oneBinding.obValue = ulOffset + offsetof(COLUMNDATA, bData);
oneBinding.obLength = ulOffset + offsetof(COLUMNDATA, dwLength);
oneBinding.obStatus = ulOffset + offsetof(COLUMNDATA, dwStatus);
oneBinding.cbMaxLen = 1; // Size of varchar column.
oneBinding.pTypeInfo = NULL;
oneBinding.pObject = NULL;
oneBinding.pBindExt = NULL;
oneBinding.dwFlags = 0;
oneBinding.eParamIO = DBPARAMIO_NOTPARAM;
oneBinding.dwMemOwner = DBMEMOWNER_CLIENTOWNED;
oneBinding.bPrecision = 0;
oneBinding.bScale = 0;
oneBinding.wType = DBTYPE_BOOL;
ulOffset = oneBinding.cbMaxLen + offsetof(COLUMNDATA, bData);
ulOffset = ROUND_UP(ulOffset, COLUMN_ALIGNVAL);
if (FAILED(hr =
pIFastLoad->QueryInterface(IID_IAccessor, (void**)&pIAccessor)))
return hr;
if (FAILED(hr = pIAccessor->CreateAccessor(DBACCESSOR_ROWDATA,
1,
&oneBinding,
ulOffset,
&hAccessor,
&oneStatus)))
return hr;
// Set up memory buffer.
pData = new BYTE[40];
if (!(pData /* = new BYTE[40]*/)) {
hr = E_FAIL;
goto cleanup;
}
pcolData = (COLUMNDATA*)pData;
pcolData->dwLength = 1;
pcolData->dwStatus = 0;
for (i = 0; i < 10; i++)
{
if (i % 2 == 0)
{
pcolData->bData[0] = 0x00;
}
else
{
pcolData->bData[0] = 0xFF;
}
if (FAILED(hr = pIFastLoad->InsertRow(hAccessor, pData)))
goto cleanup;
}
It's entirely likely that I'm putting the wrong value into the buffer, or have some other constant value incorrect. I did find an article describing the safety of various data type conversions and it looks like byte to bool is safe... but how would the buffer know what kind of data I'm putting in there if it's just a byte array?

Answer 1

Figured this out, I had not correctly switched over the demo from loading strings to fixed-width values. For strings, the data blob gets a 1-width pointer to the value whereas fixed-width values get the actual data.
So my COLUMNDATA struct now looks like this:
// How to lay out each column in memory.
struct COLUMNDATA {
DBLENGTH dwLength; // Length of data (not space allocated).
DWORD dwStatus; // Status of column.
VARIANT_BOOL bData; // Value, or if a string, a pointer to the value.
};
With the relevant length fix here:
pcolData = (COLUMNDATA*)pData;
pcolData->dwLength = sizeof(VARIANT_BOOL); // using a short.. make it two
pcolData->dwStatus = DBSTATUS_S_OK; // Indicates that the data value is to be used, not null
And the little value-setting for loop looks like this:
for (i = 0; i < 10; i++)
{
if (i % 2 == 0)
{
pcolData->bData = VARIANT_TRUE;
}
else
{
pcolData->bData = VARIANT_FALSE;
}
if (FAILED(hr = pIFastLoad->InsertRow(hAccessor, pData)))
goto cleanup;
}
I've updated the repository with the working code. I was inspired to make this change after reading the documentation for the obValue property.