Most systems of this nature rely on the primary key as the natural unique identifier, I would really suggest you stick with that, and subclass for different DBDs.

I'm not sure that I entirely agree with that. It's legitimate to have another unique identifier. You just don't want to be using it as a foreign key in another table. The argument for having surrogate primary keys is that they are meaningless as anything except a row identifier, having no semantic meaning as far as your data is concerned, and thus are non-volatile and consequently safe to use for linking objects/rows together.

I agree with your assertion that subclassing is the right thing to do. I just don't think that the primary key has to be the only unique identifier. For example, think of a user table... The user id is going to be unique. It would be a bad idea to use it as a foreign key in link tables, but it would be unique all the same.

Anyway, I'm not sure what I'm arguing anymore... I didn't get enough sleep last night and am not entirely coherent. :-)

In reply to Re^4: Auto-Increment and DBD Agnosticism by skyknight
in thread Auto-Increment and DBD Agnosticism by skyknight

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