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From Craig L Russell <Craig.Russ...@Sun.COM>
Subject Re: "generated by default" question
Date Tue, 13 Jun 2006 16:11:40 GMT
Hi Mikey,

On Jun 12, 2006, at 10:05 PM, derby@segel.com wrote:

> [mjs]
> I believe the problem is in how you're interpreting clause 3):
> "
>       3) If there exists a non-negative integer N such that SMIN <=  
> CBV + N
>          * INC <= SMAX and the value (CBV + N * INC) has not  
> already been
>          returned in the current cycle, then let V1 be (CBV + N *
>          INC). Otherwise, ...
> "
> -=-
>
> It doesn't say what N is. That is to say...
> Suppose you have a sequence 0,1,2,3,4 inserted so that the next number
> should be 5. Yet suppose someone inserts a row with 5. Thus when  
> you try to
> use 5, you generate an error. In sub-section 3), N could =6 or any  
> number >6
> but less than the MAX value of an integer.
>
> It can be interpreted that the sequence should attempt to generate  
> N such
> that it doesn't fail on the insert....
>
> This is where the idea of selecting the MAX() value in the identity  
> column
> and incrementing it by one for the failed insert.
>
> And that would be a compliant solution.

As I read this part of the specification, it refers to the generation  
of the sequence number, and not to the usage. The trick phrase is  
"the value (CBV + N * INC) has not already been returned in the  
current cycle". As I understand "returned" it means returned by the  
sequence generator, and nothing to do with the usage as a column value.

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.

Regards,

Craig

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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