Re: Datastore identity strategy

[Craig L Russell]

Hi Andy,

On Mar 28, 2006, at 10:33 PM, Andy Jefferson wrote:

Hi Craig,

Using both identity and sequence makes sense for schema generation
where you want the identity strategy (JDO implementation doesn't
generate key values) and automatic key generation using the sequence
named (JDO implementation generates the trigger and stored procedure
to use the named sequence).

currently.

what the impl was doing ? ;-)

JPOX doesn't support creation of trigger/storedproc for using sequences like this We could just retrieve the value from the sequence and use that in the INSERT (which is what we do with strategy="sequence" anyway). Whether the JDO impl uses triggers/storedprocs is its decision isn't it ? How would a TCK be able to check

The TCK doesn't require an implementation to generate schema. So the only thing you would have to do in case of strategy="identity" is to stay out of the database's way. Assume the keys are generated (which means that you need to use the getGeneratedKeys method to retrieve the keys after an insert operation.

So how do you specify MySQL "autoincrement" if you remove this ?
They aren't "IDENTITY" type.

It seems that the functionality is identical to IDENTITY as defined
by SQL 2003.

Internally JPOX treats "identity" and "autoassign" identically, so this part would actually simplify things slightly for us, and causes no issue that I know of.

Cool.

I'd say strategy="identity" with no sequence means use the
GENERATED ... AS IDENTITY.

Yes, or "autoincrement", or probably "SERIAL" too.

strategy="identity" with sequence also specified means use a trigger
and stored procedure to generate key values.

Yes, but with my comments above.

strategy="sequence" means use the named sequence explicitly in insert

statements, as in INSERT INTO EMPLOYEE (ID, NAME) VALUES
(named_sequence.nextval, ?).


likely do the "nextval" call first and plug the value into the INSERT.

Yes, although the implementation needs to know the value being used so would

Craig

I've confirmed with the JDBC4 spec lead that you can retrieve the keys using getGeneratedKeys if you use this strategy.

--
Andy

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

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