Streaming Support for BLOB Output Parameters
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Azure Synapse Analytics
Analytics Platform System (PDW)
This article contains a sample that shows streaming support for BLOB output parameters, which binds BLOB output parameters as ISequentialStreams.
You can become blocked on output parameters in IMultipleResults::GetResult, receiving DB_E_OBJECTOPEN return value. The caller should check for pending blob parameters, and either read them completely or release them.
Example
Code
// blob_out_param.cpp
#ifndef UNICODE
#define UNICODE
#endif
#define DBINITCONSTANTS
#define INITGUID
#include <windows.h>
// Change the following to match your server and test database,
// and also the 'use' statement in the setup SQL that follows
const WCHAR* g_wchServerName = L".";
const WCHAR* g_wchDBName = L"TestDB";
const WCHAR* g_wchSecurity = L"SSPI";
/*
// Execute the following before running the program
use TestDB
go
drop proc Scenario1
go
drop table tScenario1
go
create table tScenario1 (c1 int, c2 varchar(20))
go
insert into tScenario1 values (1, 'abcdefgh')
insert into tScenario1 values (2, 'ijklm')
insert into tScenario1 values (3, 'nopqr')
insert into tScenario1 values (4, 'stuvwxyz')
go
create proc Scenario1 @p1 int output, @p2 varchar(max) output, @p3 xml output, @p4 varchar(20) output
as
begin
set @p1 = @p1 + 5
set @p2 = replicate(convert(varchar(max), 'a'), 10000)
set @p3 = '<tag1>Some text</tag1>'
set @p4 = '@p4 varchar(20)'
select * from tScenario1
return datalength(@p2)
end
go
------------------------- TESTING CODE -------------------------
declare @v1 int
set @v1 = 16
declare @v2 varchar(max)
declare @v3 xml
declare @v4 varchar(20)
declare @ret_val int
exec @ret_val = Scenario1 @v1 output, @v2 output, @v3 output, @v4 output
print @v1
print @v2
print convert(nchar, @v3)
print @v4
print @ret_val
go
*/
#include <stdio.h>
#include <stddef.h>
#include <iostream>
#include <oledb.h>
#include <oledberr.h>
#include <msoledbsql.h>
#include <oledberr.h>
#include <iostream>
#include <tchar.h>
using namespace std;
#define CHKHR_GOTO(hr, lblExit, szMsg) \
do \
{ \
if (FAILED(hr)) \
{ \
cout << szMsg << endl; \
goto lblExit; \
} \
} \
while (0)
#define RELEASE_ITF(pItf) \
if (pItf) \
{ \
pItf->Release(); \
pItf = NULL; \
}
#define INIT_BINDINGS(acDBBinding, nBindings) \
for (int uIndex = 0; uIndex < nBindings; uIndex++) {\
acDBBinding[uIndex].iOrdinal = uIndex + 1; \
acDBBinding[uIndex].obLength = 0; \
acDBBinding[uIndex].obStatus = 0; \
acDBBinding[uIndex].pTypeInfo = NULL; \
acDBBinding[uIndex].pObject = NULL; \
acDBBinding[uIndex].pBindExt = NULL; \
acDBBinding[uIndex].dwPart = DBPART_VALUE; \
acDBBinding[uIndex].dwMemOwner = DBMEMOWNER_CLIENTOWNED; \
acDBBinding[uIndex].dwFlags = 0; \
acDBBinding[uIndex].bScale = 0; \
}
IDBInitialize* pIDBInitialize = NULL;
HRESULT Connect(ICommandText** ppICommandText) {
HRESULT hr;
IDBProperties* pIDBProperties = NULL;
IDBCreateSession* pIDBCreateSession = NULL;
IDBCreateCommand* pIDBCreateCommand = NULL;
ICommandText* pICommandText = NULL;
const ULONG nInitProps = 3;
const ULONG nPropSet = 1;
DBPROP InitProperties[nInitProps];
DBPROPSET InitPropSet[nPropSet];
*ppICommandText = NULL;
hr = CoInitialize(NULL);
CHKHR_GOTO(hr, _ExitConnect, "Unable to Initialize COM.");
hr = CoCreateInstance(CLSID_MSOLEDBSQL, NULL, CLSCTX_INPROC_SERVER, IID_IDBInitialize, (void **)&pIDBInitialize);
CHKHR_GOTO(hr, _ExitConnect, "Unable to Load MSOLEDBSQL.");
for (ULONG uIndexProp = 0; uIndexProp < nInitProps; uIndexProp++) {
VariantInit(&InitProperties[uIndexProp].vValue);
InitProperties[uIndexProp].vValue.vt = VT_BSTR;
InitProperties[uIndexProp].dwOptions = DBPROPOPTIONS_REQUIRED;
InitProperties[uIndexProp].colid = DB_NULLID;
}
InitProperties[0].dwPropertyID = DBPROP_INIT_DATASOURCE;
InitProperties[0].vValue.bstrVal = SysAllocString(g_wchServerName);
InitProperties[1].dwPropertyID = DBPROP_INIT_CATALOG;
InitProperties[1].vValue.bstrVal = SysAllocString(g_wchDBName);
InitProperties[2].dwPropertyID = DBPROP_AUTH_INTEGRATED;
InitProperties[2].vValue.bstrVal = SysAllocString(g_wchSecurity);
InitPropSet[0].guidPropertySet = DBPROPSET_DBINIT;
InitPropSet[0].cProperties = 3;
InitPropSet[0].rgProperties = InitProperties;
hr = pIDBInitialize->QueryInterface(IID_IDBProperties, (void **)&pIDBProperties);
CHKHR_GOTO(hr, _ExitConnect, "Failed to obtain IDBProperties interface.");
hr = pIDBProperties->SetProperties(nPropSet, InitPropSet);
CHKHR_GOTO(hr, _ExitConnect, "Failed to Set Initialization properties.");
hr = pIDBInitialize->Initialize();
CHKHR_GOTO(hr, _ExitConnect, "Failed to Connect to the Server.");
//Create a new activity from the data source object.
hr = pIDBInitialize->QueryInterface(IID_IDBCreateSession, (void**)&pIDBCreateSession);
CHKHR_GOTO(hr, _ExitConnect, "Failed to obtain IDBCreateSession interface.");
hr = pIDBCreateSession->CreateSession(NULL, IID_IDBCreateCommand, (IUnknown**)&pIDBCreateCommand);
CHKHR_GOTO(hr, _ExitConnect, "Failed to create a new Session.");
hr = pIDBCreateCommand->CreateCommand(NULL, IID_ICommandText, (IUnknown**)&pICommandText);
CHKHR_GOTO(hr, _ExitConnect, "Failed to create a new Command.");
*ppICommandText = pICommandText;
_ExitConnect:
RELEASE_ITF(pIDBCreateCommand);
for (ULONG uIndexProp = 0; uIndexProp < nInitProps; uIndexProp++)
VariantClear(&InitProperties[uIndexProp].vValue);
RELEASE_ITF(pIDBProperties);
return hr;
}
HRESULT DisConnect() {
HRESULT hr = S_OK;
if (pIDBInitialize)
hr = pIDBInitialize->Uninitialize();
RELEASE_ITF(pIDBInitialize);
return hr;
}
int main() {
HRESULT hr;
const WCHAR* g_wchCmdString = L"{? = call Scenario1 ( ?, ?, ?, ?)};{? = call Scenario1 ( ?, ?, ?, ?)}";
ICommandText* pICommandText = NULL;
IAccessor* pIAccessor = NULL;
HACCESSOR hAccessor = NULL;
IRowset* pIRowset = NULL;
IMultipleResults* pIMultipleResults = NULL;
ISequentialStream* pIStream = NULL;
const ULONG nParams = 10;
ULONG uIndex = 0;
DBBINDING acDBBinding[nParams];
DBBINDSTATUS acDBBindStatus[nParams];
typedef struct tagSPROCPARAMS {
long lReturnValue;
long lInt;
IUnknown* streamVarcharMax;
IUnknown* streamXML;
char chVarChar[21];
long lReturnValue2;
long lInt2;
IUnknown* streamVarcharMax2;
IUnknown* streamXML2;
char chVarChar2[21];
} SPROCPARAMS;
SPROCPARAMS sprocparams[] = { { 6, 17, NULL, NULL, "", 4, 20, NULL, NULL, "" },{ 5, 23, NULL, NULL, "", 7, 11, NULL, NULL, "" } };
const int nBlobBindingIndexes = 8;
IUnknown** ppBoundBlobs[nBlobBindingIndexes];
int idxBlobBindingCurrent = 0;
ppBoundBlobs[0] = &(sprocparams[0].streamVarcharMax);
ppBoundBlobs[1] = &(sprocparams[0].streamXML);
ppBoundBlobs[2] = &(sprocparams[0].streamVarcharMax2);
ppBoundBlobs[3] = &(sprocparams[0].streamXML2);
ppBoundBlobs[4] = &(sprocparams[1].streamVarcharMax);
ppBoundBlobs[5] = &(sprocparams[1].streamXML);
ppBoundBlobs[6] = &(sprocparams[1].streamVarcharMax2);
ppBoundBlobs[7] = &(sprocparams[1].streamXML2);
DBROWCOUNT cNumRows;
DBPARAMS Params;
hr = Connect(&pICommandText);
if (FAILED(hr))
goto _Exit;
hr = pICommandText->SetCommandText(DBGUID_DBSQL, g_wchCmdString);
CHKHR_GOTO(hr, _Exit, "Failed to Set Command Text.");
hr = pICommandText->QueryInterface(IID_IAccessor, (void**)&pIAccessor);
CHKHR_GOTO(hr, _Exit, "Failed to get IAccessor interface on Command object.");
INIT_BINDINGS(acDBBinding, nParams);
acDBBinding[0].obValue = offsetof(SPROCPARAMS, lReturnValue);
acDBBinding[0].eParamIO = DBPARAMIO_OUTPUT;
acDBBinding[0].cbMaxLen = sizeof(sprocparams[0].lReturnValue);
acDBBinding[0].wType = DBTYPE_I4;
acDBBinding[0].bPrecision = 11;
acDBBinding[1].obValue = offsetof(SPROCPARAMS, lInt);
acDBBinding[1].eParamIO = DBPARAMIO_INPUT | DBPARAMIO_OUTPUT;
acDBBinding[1].cbMaxLen = sizeof(sprocparams[0].lInt);
acDBBinding[1].wType = DBTYPE_I4;
acDBBinding[1].bPrecision = 11;
acDBBinding[2].obValue = offsetof(SPROCPARAMS, streamVarcharMax);
acDBBinding[2].eParamIO = DBPARAMIO_OUTPUT;
acDBBinding[2].cbMaxLen = sizeof(sprocparams[0].streamVarcharMax);
acDBBinding[2].wType = DBTYPE_IUNKNOWN;
acDBBinding[2].pObject = new DBOBJECT;
acDBBinding[2].pObject->dwFlags = STGM_READ;
acDBBinding[2].pObject->iid = IID_ISequentialStream;
acDBBinding[2].bPrecision = 255;
acDBBinding[3].obValue = offsetof(SPROCPARAMS, streamXML);
acDBBinding[3].eParamIO = DBPARAMIO_OUTPUT;
acDBBinding[3].cbMaxLen = sizeof(sprocparams[0].streamXML);
acDBBinding[3].wType = DBTYPE_IUNKNOWN;
acDBBinding[3].pObject = new DBOBJECT;
acDBBinding[3].pObject->dwFlags = STGM_READ;
acDBBinding[3].pObject->iid = IID_ISequentialStream;
acDBBinding[3].bPrecision = 255;
acDBBinding[4].obValue = offsetof(SPROCPARAMS, chVarChar);
acDBBinding[4].eParamIO = DBPARAMIO_OUTPUT;
acDBBinding[4].cbMaxLen = sizeof(sprocparams[0].chVarChar);
acDBBinding[4].wType = DBTYPE_STR;
acDBBinding[4].bPrecision = 255;
acDBBinding[5].obValue = offsetof(SPROCPARAMS, lReturnValue2);
acDBBinding[5].eParamIO = DBPARAMIO_OUTPUT;
acDBBinding[5].cbMaxLen = sizeof(sprocparams[0].lReturnValue2);
acDBBinding[5].wType = DBTYPE_I4;
acDBBinding[5].bPrecision = 11;
acDBBinding[6].obValue = offsetof(SPROCPARAMS, lInt2);
acDBBinding[6].eParamIO = DBPARAMIO_INPUT | DBPARAMIO_OUTPUT;
acDBBinding[6].cbMaxLen = sizeof(sprocparams[0].lInt2);
acDBBinding[6].wType = DBTYPE_I4;
acDBBinding[6].bPrecision = 11;
acDBBinding[7].obValue = offsetof(SPROCPARAMS, streamVarcharMax2);
acDBBinding[7].eParamIO = DBPARAMIO_OUTPUT;
acDBBinding[7].cbMaxLen = sizeof(sprocparams[0].streamVarcharMax2);
acDBBinding[7].wType = DBTYPE_IUNKNOWN;
acDBBinding[7].pObject = new DBOBJECT;
acDBBinding[7].pObject->dwFlags = STGM_READ;
acDBBinding[7].pObject->iid = IID_ISequentialStream;
acDBBinding[7].bPrecision = 255;
acDBBinding[8].obValue = offsetof(SPROCPARAMS, streamXML2);
acDBBinding[8].eParamIO = DBPARAMIO_OUTPUT;
acDBBinding[8].cbMaxLen = sizeof(sprocparams[0].streamXML2);
acDBBinding[8].wType = DBTYPE_IUNKNOWN;
acDBBinding[8].pObject = new DBOBJECT;
acDBBinding[8].pObject->dwFlags = STGM_READ;
acDBBinding[8].pObject->iid = IID_ISequentialStream;
acDBBinding[8].bPrecision = 255;
acDBBinding[9].obValue = offsetof(SPROCPARAMS, chVarChar2);
acDBBinding[9].eParamIO = DBPARAMIO_OUTPUT;
acDBBinding[9].cbMaxLen = sizeof(sprocparams[0].chVarChar2);
acDBBinding[9].wType = DBTYPE_STR;
acDBBinding[9].bPrecision = 255;
hr = pIAccessor->CreateAccessor(
DBACCESSOR_PARAMETERDATA,
nParams,
acDBBinding,
sizeof(SPROCPARAMS),
&hAccessor,
acDBBindStatus);
CHKHR_GOTO(hr, _Exit, "Failed to Create Accessor for the defined parameters.");
Params.pData = &sprocparams;
Params.cParamSets = sizeof(sprocparams) / sizeof(SPROCPARAMS);
Params.hAccessor = hAccessor;
hr = pICommandText->Execute(NULL, IID_IMultipleResults, &Params, &cNumRows, (IUnknown**)&pIMultipleResults);
CHKHR_GOTO(hr, _Exit, "Failed to Execute Command.");
cout << "Command executed successfully, retrieving results." << endl;
idxBlobBindingCurrent = 0;
if (pIMultipleResults) {
for (;;) {
hr = pIMultipleResults->GetResult(NULL, 0, IID_IRowset, NULL, (IUnknown**)&pIRowset);
if (hr == DB_S_NORESULT) {
cout << "All results processed." << endl;
break;
}
if (FAILED(hr)) {
// In this case, user has open rowset or open blobs
if (hr == DB_E_OBJECTOPEN) {
IUnknown* pIUnkCurrent = *ppBoundBlobs[idxBlobBindingCurrent];
if (pIUnkCurrent) {
hr = pIUnkCurrent->QueryInterface(IID_ISequentialStream, (void**)&pIStream);
if (FAILED(hr)) {
cout << "Failed to get a stream object. " << endl;
goto _Exit;
}
RELEASE_ITF(pIUnkCurrent);
// Display the data
char chBuff[51];
wchar_t wchBuff[51];
ULONG cbRead = 0;
do {
if (idxBlobBindingCurrent % 2) {
hr = pIStream->Read(wchBuff, 50 * sizeof(wchar_t), &cbRead);
if (hr == E_UNEXPECTED)
break;
wchBuff[cbRead / 2] = 0;
printf_s("%S", wchBuff[0] == 0xFEFF ? wchBuff + 1 : wchBuff);
if (hr == S_FALSE || cbRead < 50 * sizeof(wchar_t)) {
cout << endl;
RELEASE_ITF(pIStream);
break;
}
}
else {
hr = pIStream->Read(chBuff, 50, &cbRead);
if (hr == E_UNEXPECTED)
break;
chBuff[cbRead] = 0;
printf_s("%s", chBuff);
if (hr == S_FALSE || cbRead < 50) {
cout << endl;
RELEASE_ITF(pIStream);
break;
}
}
} while (SUCCEEDED(hr));
if (FAILED(hr) && hr != E_UNEXPECTED) {
cout << "Stream data read failed." << endl;
goto _Exit;
}
idxBlobBindingCurrent++;
continue;
}
}
else {
cout << "GetResult failed with unknown error." << endl;
break;
}
}
else {
if (pIRowset) {
DBCOUNTITEM cRowsObtained;
DBCOUNTITEM cRowsTotal = 0;
HROW hRow[1];
HROW* phRow = hRow;
do {
hr = pIRowset->GetNextRows(0, 0, 1, &cRowsObtained, &phRow);
cRowsTotal += cRowsObtained;
pIRowset->ReleaseRows(cRowsObtained, hRow, NULL, NULL, NULL);
} while (SUCCEEDED(hr) && hr != DB_S_ENDOFROWSET);
cout << "Total number of Rows: " << cRowsTotal << endl;
}
RELEASE_ITF(pIRowset);
}
}
}
// Now display the rest of parameters
printf_s(" lReturnValue : %d\n", sprocparams[0].lReturnValue);
printf_s(" lInt : %d\n", sprocparams[0].lInt);
printf_s(" chVarChar : %s\n", sprocparams[0].chVarChar);
printf_s(" lReturnValue : %d\n", sprocparams[0].lReturnValue2);
printf_s(" lInt : %d\n", sprocparams[0].lInt2);
printf_s(" chVarChar : %s\n", sprocparams[0].chVarChar);
printf_s(" lReturnValue : %d\n", sprocparams[1].lReturnValue);
printf_s(" lInt : %d\n", sprocparams[1].lInt);
printf_s(" chVarChar : %s\n", sprocparams[1].chVarChar);
printf_s(" lReturnValue : %d\n", sprocparams[1].lReturnValue2);
printf_s(" lInt : %d\n", sprocparams[1].lInt2);
printf_s(" chVarChar : %s\n", sprocparams[1].chVarChar);
_Exit:
RELEASE_ITF(pIStream);
RELEASE_ITF(pIRowset);
RELEASE_ITF(pIMultipleResults);
if (pIAccessor) {
pIAccessor->ReleaseAccessor(hAccessor, NULL);
RELEASE_ITF(pIAccessor);
}
RELEASE_ITF(pICommandText);
DisConnect();
}