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From Michael Segel <mse...@segel.com>
Subject Re: "generated by default" question
Date Tue, 13 Jun 2006 19:14:03 GMT
On Tuesday 13 June 2006 1:19 pm, Craig L Russell wrote:
> Hi,
>
> On Jun 13, 2006, at 11:01 AM, Craig L Russell wrote:
> >>> In fact, you could argue that if the implementation skipped
> >>> returning
> >>> a sequence value just because that value had been inserted by the
> >>> user into a column, it would be a bug.
>
> I withdraw this argument after re-reading the words. It is legal to
> skip over some number of values as long as you remember which values
> were skipped over so that you don't cycle before returning all of them.
>
> Craig
>
Yup.
Thats why if on inserts where the user enters a value, if you check to see 
that the value is > CBV and that the row inserted ok, then you reset your CBV 
to that value +1. (Assuming that the increment is 1).

That will ensure that for the first cycle, you'll never throw a unique 
exception.... ;-) Its a neat little trick and since the sequence Object and 
the row entered with still be in memory, it would be a very, fast and 
efficient way to handle this problem in the short term. ;-)

Kind of a neat trick. I imagine this is what they did when they developed the 
serial column and probably carried it over to their sequences.
(Anyone at IBM care to comment? ;-)

-G

PS. The solution gets murky when you have to have multiple iterations or 
cycles. But that doesn't mean you can't find a solution that would still work 
and be efficient.

> Craig Russell
> Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
> 408 276-5638 mailto:Craig.Russell@sun.com
> P.S. A good JDO? O, Gasp!

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