Re: Mixing OO and DB
Date: Sat, 8 Mar 2008 15:57:56 -0800 (PST)
Message-ID: <04811571-c9e6-4793-96d8-a4acb8ef7020_at_e10g2000prf.googlegroups.com>
On Mar 8, 3:37 am, rp..._at_pcwin518.campus.tue.nl (rpost) wrote:
>
> In the context of a single application with a variety of storage
> backends, which is what the OO world usually thinks of, and Robert Martin
> in this case, abstraction means providing a common application/storage
> interface that allows storage backends to be added and replaced without
> any change to the common application code.
This is certainly *possible* to do. But there is a significant issue involved, relative to the comparative expressive power of the storage backends being considered. (To say nothing of the issue of compatibility of the computational model of the backends.) If we are, for example, comparing a flat file backend to a SQL database backend, we have a serious mismatch if we want to address them with a single polymorphic interface.
There are exactly two ways to address this mismatch. One is to write a data management language on par with SQL that is backed by a flat file. This will bring the flat file interface up to the power of the SQL interface. It is essentially the same job as writing a SQL DBMS. The other way is to limit one's use of SQL to something comparably powerful to flat files: read/write/seek. This, plus a little bit, is about all most ORMs do.
Of course, to someone who knows how to leverage SQL well, either option is a horror.
Am I overstating the case here? A bit, yes. But not much.
As to the specific point you were making, though, it was an excellent one.
Marshall Received on Sun Mar 09 2008 - 00:57:56 CET