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Use Large CLR UDTs (OLE DB)

This sample shows how to fetch rows with large user-defined types from a result set. For more information, see Large CLR User-Defined Types (OLE DB). This sample works with SQL Server 2008 or later.

This sample contains two projects. One project creates an assembly (DLL) from C# source code. This assembly contains the CLR type. A table will be added to the database. A column in the table will be of a type defined in the assembly, By default, this sample will use the master database. The second project is a native C application that reads data from the table.

Compile the first (C#) code listing to a DLL. Then, copy the DLL to the root directory of the C drive.

Execute the second (Transact-SQL) code listing to add the assembly to the master database.

Compile with ole32.lib oleaut32.lib and execute the third (C++) code listing. This application connects to your computer's default SQL Server instance. On some Windows operating systems, you will need to change (localhost) or (local) to the name of your SQL Server instance. To connect to a named instance, change the connection string from L"(local)" to L"(local)\\name" , where name is the named instance. By default, SQL Server Express installs to a named instance. Make sure your INCLUDE environment variable includes the directory that contains sqlncli.h.

Execute the fourth (Transact-SQL) code listing to delete the assembly to the master database.

// compile with: /target: library
using System;
using System.Data;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;
using System.Text;

[assembly: System.CLSCompliantAttribute(true)]
[Serializable]
[Microsoft.SqlServer.Server.SqlUserDefinedType(Format.UserDefined, IsFixedLength = false, MaxByteSize = -1, IsByteOrdered = true)]
public class LargeStringUDT : INullable, IBinarySerialize {
    private bool _isNull;
    private string _largeString;

    public bool IsNull {
        get {
            return (_isNull);
        }
    }

    public static LargeStringUDT Null {
        get {
            LargeStringUDT lsUDT = new LargeStringUDT();
            lsUDT._isNull = true;
            return lsUDT;
        }
    }

    public override string ToString() {
        if (IsNull)
            return "NULL";
        else
            return _largeString;
    }

    [SqlMethod(OnNullCall = false)]
    public static LargeStringUDT Parse(SqlString s) {
        if (s.IsNull)
            return Null;

        LargeStringUDT lsUDT = new LargeStringUDT();
        lsUDT._largeString = s.Value;
        return lsUDT;
    }

    public String LargeString {
        get {
            return _largeString;
        }

        set {
            _largeString = value;
        }
    }

    public void Read(System.IO.BinaryReader r) {
        _isNull = r.ReadBoolean();
        if (!_isNull)
            _largeString = new String(r.ReadChars(r.ReadInt32()));
    }

    public void Write(System.IO.BinaryWriter w) {
        w.Write(_isNull);
        if (!_isNull) {
            w.Write(_largeString.Length);
            for (int i = 0; i < _largeString.Length; ++i)
                w.Write(_largeString[i]);
        }
    }
}
USE [MASTER]
GO

CREATE ASSEMBLY LargeStringUDT
FROM 'C:\LargeStringUDT.dll'
WITh PERMISSION_SET=SAFE;
GO

CREATE TYPE dbo.LargeStringUDT 
EXTERNAL NAME LargeStringUDT.[LargeStringUDT];
GO

CREATE TABLE dbo.LargeStringUDTs
(ID int IDENTITY(1,1) PRIMARY KEY, LargeString LargeStringUDT)
GO

INSERT INTO dbo.LargeStringUDTs (LargeString) VALUES (CONVERT(LargeStringUDT, 'This is the first string'));
INSERT INTO dbo.LargeStringUDTs (LargeString) VALUES (CONVERT(LargeStringUDT, 'This is the second string'));
INSERT INTO dbo.LargeStringUDTs (LargeString) VALUES (Convert(LargeStringUDT, 'This is the third string'));
GO
// compile with: ole32.lib oleaut32.lib
// Gives length of an array
#define ARRAY_SIZE(rgArray) (sizeof(rgArray)/sizeof(*rgArray))
#define NUMELEM(rgArray) ARRAY_SIZE(rgArray)

#define DBINITCONSTANTS
#define INITGUID

#define OLEDBVER 0x0250   // to include correct interfaces

#define ROUND_UP_MINIMUM 8

#define ROUND_UP(valueToRound) \
   (((valueToRound) + (ROUND_UP_MINIMUM - 1)) & ~(ROUND_UP_MINIMUM - 1))

#include <stdio.h>
#include <tchar.h>
#include <stddef.h>
#include <windows.h>
#include <iostream>
#include <oledb.h>
#include <SQLNCLI.h>

using namespace std;

// Arrangement of column data when standard rowbuffer layout is used.
struct COLUMNDATA {
   DBLENGTH dwLength;   // length of data (not space allocated)
   DBSTATUS dwStatus;   // status of column
#ifdef _WIN64
   // rgbData needs to be COLUMN_ALIGNVAL byte aligned. This fixes it for 64 bit build.
   DWORD dwAlign;
#endif
   BYTE rgbData[1];   // data here and beyond
};

int InitializeAndEstablishConnection();
int ProcessResultSet();

IDBInitialize* pIDBInitialize = NULL;
IDBProperties* pIDBProperties = NULL;
IDBCreateSession* pIDBCreateSession = NULL;
IDBCreateCommand* pIDBCreateCommand = NULL;
ICommandText* pICommandText = NULL;
IRowset* pIRowset = NULL;
IColumnsInfo* pIColumnsInfo = NULL;
ISequentialStream* pISequentialStream;

DBCOLUMNINFO* pDBColumnInfo = NULL;
IAccessor* pIAccessor =  NULL;
DBPROP InitProperties[4];
DBPROPSET rgInitPropSet[1];

ULONG i, j;
HRESULT hr;
DBROWCOUNT cNumRows = 0;
DBORDINAL lNumCols;
WCHAR* pStringsBuffer;
DBBINDING* pBindings;
HACCESSOR hAccessor;
DBCOUNTITEM lNumRowsRetrieved;
HROW hRows[10];
HROW* pRows = &hRows[0];

int main() {
   // The command to execute.
   WCHAR* wCmdString = OLESTR("SELECT ID, LargeString FROM dbo.LargeStringUDTs");

   // Call a function to initialize and establish connection. 
   if (InitializeAndEstablishConnection() == -1) {
      cout << "Failed to initialize and connect to the server.\n";
      return -1;
   }

   // Create a session 
   if (FAILED(pIDBInitialize->QueryInterface( IID_IDBCreateSession, (void**) &pIDBCreateSession))) {
         cout << "Failed to obtain IDBCreateSession interface.\n";
         return -1;
   }

   if (FAILED(pIDBCreateSession->CreateSession( NULL, IID_IDBCreateCommand, (IUnknown**) &pIDBCreateCommand))) {
         cout << "pIDBCreateSession->CreateSession failed.\n";
         return -1;
   }

   // Access the ICommandText interface.
   if (FAILED(pIDBCreateCommand->CreateCommand( NULL, IID_ICommandText, (IUnknown**) &pICommandText))) {
         cout << "Failed to access ICommand interface.\n";
         return -1;
   }

   // Specify the command text.
   if (FAILED(pICommandText->SetCommandText(DBGUID_DBSQL, wCmdString))) {
      cout << "Failed to set command text.\n";
      return -1;
   }

   // Execute the command.
   if (FAILED(hr = pICommandText->Execute( NULL, IID_IRowset, NULL, &cNumRows, (IUnknown **) &pIRowset))) {
         cout << "Failed to execute command.\n";
         return -1;
   }

   // Process the result set.
   ProcessResultSet(); 

   pIRowset->Release();

   // release memory.
   pICommandText->Release();
   pIDBCreateCommand->Release();
   pIDBCreateSession->Release();

   if (FAILED(pIDBInitialize->Uninitialize())) {
      // Uninitialize is not required, but it fails if an interface has not been released.  This can be used for debugging.
      cout << "Problem uninitializing.\n";
   }

   pIDBInitialize->Release();
   CoUninitialize();
};

int InitializeAndEstablishConnection() {    
   CoInitialize(NULL);

   // Obtain access to the SQLNCLI provider.
   hr = CoCreateInstance( CLSID_SQLNCLI11, NULL, CLSCTX_INPROC_SERVER, IID_IDBInitialize, (void **) &pIDBInitialize);

   if (FAILED(hr)) {
      printf("Failed to get IDBInitialize interface.\n");
      return -1;
   }

   // Initialize the property values needed to establish the connection.
   for ( i = 0 ; i < 4 ; i++ )
      VariantInit(&InitProperties[i].vValue);

   // Server name.
   InitProperties[0].dwPropertyID = DBPROP_INIT_DATASOURCE;
   InitProperties[0].vValue.vt = VT_BSTR;
   //InitProperties[0].vValue.bstrVal= SysAllocString(L"(local)\\SQLExpress");
   InitProperties[0].vValue.bstrVal= SysAllocString(L"(local)");
   InitProperties[0].dwOptions = DBPROPOPTIONS_REQUIRED;
   InitProperties[0].colid = DB_NULLID;

   // Database.
   InitProperties[1].dwPropertyID = DBPROP_INIT_CATALOG;
   InitProperties[1].vValue.vt = VT_BSTR;
   InitProperties[1].vValue.bstrVal = SysAllocString(L"master");
   InitProperties[1].dwOptions = DBPROPOPTIONS_REQUIRED;
   InitProperties[1].colid = DB_NULLID;

   InitProperties[2].dwPropertyID = DBPROP_AUTH_INTEGRATED;
   InitProperties[2].vValue.vt = VT_BSTR;
   InitProperties[2].vValue.bstrVal = SysAllocString(L"SSPI");
   InitProperties[2].dwOptions = DBPROPOPTIONS_REQUIRED;
   InitProperties[2].colid = DB_NULLID;

   // Properties are set, now construct the DBPROPSET structure (rgInitPropSet) used to pass 
   // an array of DBPROP structures (InitProperties) to the SetProperties method.
   rgInitPropSet[0].guidPropertySet = DBPROPSET_DBINIT;
   rgInitPropSet[0].cProperties = 4;
   rgInitPropSet[0].rgProperties = InitProperties;

   // Set initialization properties.
   hr = pIDBInitialize->QueryInterface(IID_IDBProperties, (void **)&pIDBProperties);
   if (FAILED(hr)) {
      cout << "Failed to get IDBProperties interface.\n";
      return -1;
   }

   hr = pIDBProperties->SetProperties(1, rgInitPropSet); 
   if (FAILED(hr)) {
      cout << "Failed to set initialization properties.\n";
      return -1;
   }

   pIDBProperties->Release();

   // Now establish the connection to the data source.
   if (FAILED(pIDBInitialize->Initialize())) {
      cout << "Problem in establishing connection to the data"
         "source.\n";
      return -1;
   }
   return 0;
}

// Retrieve and display data resulting from a query.
int ProcessResultSet() {
   // Obtain access to the IColumnInfo interface
   hr = pIRowset->QueryInterface(IID_IColumnsInfo, (void **)&pIColumnsInfo);
   if (FAILED(hr)) {
      cout << "Failed to get IColumnsInfo interface.\n";
      return -1;
   } 

   // Retrieve the column information.
   pIColumnsInfo->GetColumnInfo(&lNumCols, &pDBColumnInfo, &pStringsBuffer);

   // Free the columninfo interface.
   pIColumnsInfo->Release();

   // Create a DBBINDING array.
   DBBINDING * p = (pBindings = new DBBINDING[lNumCols]);
   if (!(p /* pBindings = new DBBINDING[lNumCols] */ ))
      return -1;

   // There are two columns in the table.
   pBindings[0].iOrdinal = 1; 
   pBindings[0].obValue = 0;
   pBindings[0].obLength = 0;
   pBindings[0].obStatus = 0;
   pBindings[0].pTypeInfo = NULL;
   pBindings[0].pObject = NULL;
   pBindings[0].pBindExt = NULL;
   pBindings[0].dwPart = DBPART_VALUE | DBPART_LENGTH | DBPART_STATUS;
   pBindings[0].dwMemOwner = DBMEMOWNER_CLIENTOWNED;
   pBindings[0].eParamIO = DBPARAMIO_NOTPARAM;   // Count 10
   pBindings[0].cbMaxLen = sizeof(long);
   pBindings[0].dwFlags = 0;
   pBindings[0].wType = DBTYPE_I4;
   pBindings[0].bPrecision = 0;
   pBindings[0].bScale = 0; //Count 15

   pBindings[1].iOrdinal = 2; 
   pBindings[1].obValue = 0;
   pBindings[1].obLength = 0;
   pBindings[1].obStatus = 0;
   pBindings[1].pTypeInfo = NULL;
   pBindings[1].pObject = NULL;
   pBindings[1].pBindExt = NULL;
   pBindings[1].dwPart = DBPART_VALUE | DBPART_STATUS;
   pBindings[1].dwMemOwner = DBMEMOWNER_CLIENTOWNED;
   pBindings[1].eParamIO = DBPARAMIO_NOTPARAM; //Count 10
   pBindings[1].cbMaxLen = sizeof(IUnknown*);
   pBindings[1].dwFlags = 0;
   pBindings[1].wType = DBTYPE_IUNKNOWN;
   pBindings[1].bPrecision = 0;
   pBindings[1].bScale = 0; //Count 15

   DBBYTEOFFSET rowSize = 0;

   for (size_t i = 0; i < lNumCols; i++) {
      pBindings[i].obLength = rowSize + offsetof(COLUMNDATA, dwLength);
      pBindings[i].obStatus = rowSize + offsetof(COLUMNDATA, dwStatus);
      pBindings[i].obValue  = rowSize + offsetof(COLUMNDATA, rgbData);

      rowSize += offsetof(COLUMNDATA, rgbData) + pBindings[i].cbMaxLen;
      rowSize  = ROUND_UP(rowSize);
   }

   hr = pIRowset->QueryInterface(IID_IAccessor, (void **) &pIAccessor);
   if (FAILED(hr)) {
      cout << "Failed to obtain IAccessor interface.\n";
      return -1;
   }

   // Create an accessor from the set of bindings (pBindings).
   pIAccessor->CreateAccessor(DBACCESSOR_ROWDATA, lNumCols, pBindings, 0, &hAccessor, NULL);

   // Print column names.
   for ( j = 0 ; j < lNumCols ; j++ )
      printf("%-30S", pDBColumnInfo[j].pwszName);

   printf("\n");   // new line after the column names

   // Get a set of 10 row at a time.
   pIRowset->GetNextRows( NULL, 0, 10, &lNumRowsRetrieved, &pRows);

   // Allocate space for the row buffer.
   BYTE * pBuffer = new BYTE[rowSize];
   if (!(pBuffer /* = new BYTE[rowSize]; */ )) {
      // Free up all allocated memory.
      pIAccessor->ReleaseAccessor(hAccessor, NULL);
      pIAccessor->Release();
      delete [] pBindings;
      return 0;
   }

   // Display the rows.
   while ( lNumRowsRetrieved > 0 ) {
      // For each row, print the column data.
      for ( j = 0 ; j < lNumRowsRetrieved ; j++ ) {
         // Clear the buffer.
         memset(pBuffer, 0, rowSize);

         // Get the row data values.
         pIRowset->GetData(hRows[j], hAccessor, pBuffer);

         // Print the first column
         printf("%-25d", *((long*)(*(&pBuffer) + pBindings[0].obValue)));
         ULONG dwStatus = *((ULONG*) (pBuffer + pBindings[1].obStatus));

         if (dwStatus == DBSTATUS_S_ISNULL) {
            // Process NULL data
         }

         else if (dwStatus == DBSTATUS_S_OK) {
            HRESULT hrStreamRead = S_OK;
            ULONG cbRead = 0;
            BYTE DataBuff[1024];

            memset(DataBuff, 0, 1024);

            pISequentialStream = *((ISequentialStream**)(pBuffer + pBindings[1].obValue));

            do {
               hrStreamRead = pISequentialStream->Read(DataBuff, sizeof(DataBuff), &cbRead);
               if (SUCCEEDED(hrStreamRead)) {
                  // First byte indicate the value for IsNull property and the next four bytes 
                  // indicate the length of the string. So we start from the fifth byte.
                  for (ULONG i = 5; i < cbRead; i++)
                     putchar((char)DataBuff[i]);

                  printf("\n");
               }
            }
            while (hrStreamRead != S_FALSE && cbRead == sizeof(DataBuff));

            pISequentialStream->Release();
         }
         else
            // Process error from GetData.
            cout << "Failed to GetData.\n";

      } // for

      // Release the rows retrieved.
      pIRowset->ReleaseRows(lNumRowsRetrieved, hRows, NULL, NULL, NULL);

      // Get the next 10 rows.
      pIRowset->GetNextRows(NULL, 0, 10, &lNumRowsRetrieved, &pRows);
   } // while

   // Free up all allocated memory.
   delete [] pBuffer;
   pIAccessor->ReleaseAccessor(hAccessor, NULL);
   pIAccessor->Release();
   delete [] pBindings;

   return 0;
}
USE [MASTER]
IF EXISTS (SELECT * FROM sys.objects WHERE name = 'LargeStringUDTs')
   DROP TABLE LargeStringUDTs
GO


IF EXISTS (SELECT * FROM sys.types WHERE name = 'LargeStringUDT')
   DROP TYPE dbo.LargeStringUDT
GO

IF EXISTS (SELECT * FROM sys.assemblies WHERE name = 'LargeStringUDT')
   DROP ASSEMBLY LargeStringUDT
GO
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