Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!axion!vision!chris
From: chris@vision.uucp (Chris Davies)
Newsgroups: comp.databases
Subject: Re: RDBMS Portability Isses
Keywords: RDBMS Portability, X-Windows
Message-ID: <1991Jan30.123942.13058@vision.uucp>
Date: 30 Jan 91 12:39:42 GMT
References: <1991Jan28.180523.28946@lgc.com>
Reply-To: chris@vision.UUCP (Chris Davies)
Organization: VisionWare Ltd., Leeds, UK
Lines: 57

In article <1991Jan28.180523.28946@lgc.com> rubi@lgc.com ( Ernest Rubi) writes:
>[...]  I am particularly interested in 
>portability issues between Oracle and Ingres, with additional 
>interests in Sybase and Informix. Ideally, I would like to be 
>able to take a C program containg embedded SQL and X-Window calls, 
>run it through the preprocesssor of whichever RDBMS, and have the 
>expectation that the program will function the same regardless of 
>the RDBMS. Given the constraints of an industry that has not yet  [...]

(I cannot comment on the portability of X (although I would expect that to be
not too much of a problem.)

However, for the embedded SQL part - certainly not!  Trivial statements such as
	EXEC SQL SELECT ... INTO :a

might work for both ORACLE and INGRES (but not INFORMIX), but anything more,
including the actual connection to the database, is not truly portable.

I would suggest that the easiest route for you to take is to separate out
the database-specific sections into a separate source module, wrapped up in
your own functions which perform well-defined actions in a generic-looking way.
This way your program can request such things as connection to a database
with generic-looking calls such as

	boolean ConnectToDatabase(ConnStr)
	char *ConnStr;
	{
		/*
		 * Connect to database using db-specific string.  Return
		 * TRUE or FALSE to indicate success (or otherwise).
		 */
		EXEC SQL CONNECT ... ;
	}

This is the route that VisionWare took.  I found it easiest to have a separate
module for each of the databases Ingres, Informix and Oracle, rather than
use constructs such as
	#ifdef ORACLE6
		...
	#else
	#ifdef INGRES6
		...
	#else
	#ifdef INFORMIX4
		...
	#else
	#   error "No database type specified"
	#endif

Hope this is useful,

Chris
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