C++ ODBC Wrapper Classes ( SQLHANDLES ) - part 1

Question

In order to further increase my knowledge of ODBC and C++ good design practices i have decided to try my go at creating wrapper classes of the current ODBC C Api located on MSDN.  I'm mainly wanting criticism on design problems people might see.  Any advice is greatly appreciated ;) cheers

In order to avoid VTABLE overhead i have tried my best to implement simulated dynamic binding/CRTP ( which i believe i have implemented correctly )

template<class TDerived, SQLSMALLINT THandle = SQL_HANDLE_UNKNOWN>
	class __declspec(novtable) CHandle 
	{
	public:
		SQLHANDLE   m_h;
		SQLSMALLINT m_hType;

		enum { SQL_HANDLE_UNKNOWN = -1 };

	public:
		CHandle() : 
			m_h(NULL), m_hType(THandle)
		{
			_ASSERTE(m_hType != -1);
		}

		
		CHandle(SQLHANDLE h) :
			m_h(h), m_hType(THandle)
		{
			_ASSERTE(h != NULL);
			_ASSERTE(m_hType != -1);
			
			Attach(h);
		}

		void Attach(_In_ SQLHANDLE h)
		{
			_ASSERTE(h != NULL);
			_ASSERTE(m_h == NULL);
			_ASSERTE(m_hType != -1);
			
			m_h = h;
		}

		SQLHANDLE Detach()
		{
			_ASSERTE(m_h != NULL);
			_ASSERTE(m_hType != -1);
			SQLHANDLE hTemp = m_h;
			m_h = NULL;
			return hTemp;
		}

		bool Create()
		{
			_ASSERTE(m_h == NULL);
			_ASSERTE(m_hType != -1);
			
			g_rt = SQLAllocHandle(THandle, NULL, &m_h);
			_ASSERTE(SQL_SUCCEEDED(g_rt));
			if (SQL_SUCCEEDED(g_rt) == FALSE)
				return FALSE;
			
			return TRUE;
		}

		void Destroy()
		{
			_ASSERTE(m_h != NULL);
			_ASSERTE(m_hType != -1);
			
			g_rt = SQLFreeHandle(THandle, m_h);
			_ASSERTE(SQL_SUCCEEDED(g_rt));

			m_h = NULL;
			m_hType = -1;
		}

		// TODO : test setting multiple attributes
		bool SetAttribute(_In_ SQLINTEGER attribute, _In_ SQLPOINTER value)
		{
			_ASSERTE(m_h != NULL);

			return static_cast<TDerived*>(this)->_SetAttribute(attribute, value);
		}

		// TODO : test getting multiple attributes
		bool GetAttribute(_In_ SQLINTEGER attribute, _Inout_ SQLPOINTER pValue, _Inout_ SQLINTEGER* pcbWritten)
		{
			_ASSERTE(m_h != NULL);

			return static_cast<TDerived*>(this)->_GetAttribute(attribute, pValue, pcbWritten);
		}

		operator SQLHANDLE()
		{
			return m_h;
		}

	};



	class __declspec(novtable) CEnviromentHandle : 
		public CHandle< CEnviromentHandle, SQL_HANDLE_ENV>
	{
	public:


		bool _SetAttribute(_In_ SQLINTEGER attribute, _In_ SQLPOINTER value)
		{
			_ASSERTE(m_h != NULL);

			g_rt = SQLSetEnvAttr(m_h, attribute, value, SQL_NTS);
			_ASSERTE(SQL_SUCCEEDED(g_rt));
			if (SQL_SUCCEEDED(g_rt) == FALSE)
				return FALSE;
			
			return TRUE;
		}

		// TODO : i might need last parameter. For now ignoreing
		bool _GetAttribute(_In_ SQLINTEGER attribute, _Inout_ SQLPOINTER pValue, _Inout_ SQLINTEGER* pcbWritten)
		{
			_ASSERTE(m_h != NULL);

			g_rt = SQLGetEnvAttr(m_h, attribute, pValue, SQL_IS_UINTEGER, pcbWritten);
			_ASSERTE(SQL_SUCCEEDED(g_rt));
			if (SQL_SUCCEEDED(g_rt) == FALSE)
				return FALSE;
			
			return TRUE;
		}
	};

	class __declspec(novtable) CConnectionHandle : 
		public CHandle< CConnectionHandle, SQL_HANDLE_DBC>
	{
	public:

		bool _SetAttribute(_In_ SQLINTEGER attribute, _In_ SQLPOINTER value)
		{
			_ASSERTE(m_h != NULL);

			g_rt = SQLSetConnectAttr(m_h, attribute, value, SQL_NTS);
			_ASSERTE(SQL_SUCCEEDED(g_rt));
			if (SQL_SUCCEEDED(g_rt) == FALSE)
				return FALSE;
			
			return TRUE;
		}

		// TODO : i might need last parameter. For now ignoreing
		bool _GetAttribute(_In_ SQLINTEGER attribute, _Inout_ SQLPOINTER pValue, _Inout_ SQLINTEGER* pcbWritten)
		{
			_ASSERTE(m_h != NULL);

			g_rt = SQLGetConnectAttr(m_h, attribute, pValue, SQL_IS_UINTEGER, pcbWritten);
			_ASSERTE(SQL_SUCCEEDED(g_rt));
			if (SQL_SUCCEEDED(g_rt) == FALSE)
				return FALSE;
			
			return TRUE;
		}
	};


	class __declspec(novtable) CStatementHandle : 
		public CHandle< CStatementHandle, SQL_HANDLE_STMT>
	{
	public:

		bool _SetAttribute(_In_ SQLINTEGER attribute, _In_ SQLPOINTER value)
		{
			_ASSERTE(m_h != NULL);

			g_rt = SQLSetStmtAttr(m_h, attribute, value, SQL_NTS);
			_ASSERTE(SQL_SUCCEEDED(g_rt));
			if (SQL_SUCCEEDED(g_rt) == FALSE)
				return FALSE;
			
			return TRUE;
		}

		// TODO : i might need last parameter. For now ignoreing
		bool _GetAttribute(_In_ SQLINTEGER attribute, _Inout_ SQLPOINTER pValue, _Inout_ SQLINTEGER* pcbWritten)
		{
			_ASSERTE(m_h != NULL);

			g_rt = SQLGetStmtAttr(m_h, attribute, pValue, SQL_IS_UINTEGER, pcbWritten);
			_ASSERTE(SQL_SUCCEEDED(g_rt));
			if (SQL_SUCCEEDED(g_rt) == FALSE)
				return FALSE;
			
			return TRUE;
		}
	};

Answer 1

Hi v3nOm,

Welcome here.

Based on your description, you want criticism on design problems people might see; there is not a solid answer of it, so I will change the thread type to general discussion.

Thanks for your understanding.

Regards,

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Elegentin Xie [MSFT]
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