Re: Sequence Manager question

[Guido Beutler]

Hi Armin,

Armin Waibel wrote:

Hi,

Thomas Dudziak wrote:

On Tue, 6 Apr 2004, Guido Beutler wrote:


Can I choose the sequence implementation per class?
There are only a few tables which uses DB sequences. For all other 
tables the NextValImpl is ok.
The problem is that only a few tables use DB sequences.


Nope, currently not, though for an application you should choose how the
pk values are generated, and stick to this method for all tables, 
anyway.

SequenceManager implementations can only set per database (per 
jdbc-connection-descriptor). If you really need this you need a 
special SM implementation for managing different SM.
If you interested I will try to write an alpha version of such an 
implementation.

For my current problem read-only works fine so I don't think that I need 
a special sequence manager.
Maybe that a sequence manager for mixed environments (DB sequences and 
OJB sequences) maybe useful in
future. Thanks for the offer to write one!!  ;-)
For me this is not needed right now.

So if you have a mixed scenario where some pk values shall be 
generated by
the database (sequences),
and other come from the application, then I
think you probably should use the NextValImpl like this (Armin, please
correct me if I got it wrong):

* specify NextValImpl in your connection descriptor with
autoNaming='true' if you only need one sequence, or with
autoNaming='false' if you require multiple sequence
autoNaming 'true' means that OJB build a sequence name for each 
field-descriptor (parent class-descriptor) automatic, except the 
sequence name was specified in the field-descriptor
file:///E:/intellij/OJB_Experimental/db-ojb/target/doc/sequencemanager.html#sequenceName 

'false' means OJB does not try to build a sequence name and if no 
sequence name was set in field-descriptor an exception was thrown.

If I use autoNaming=false and set a sequence name, for what OJB uses the 
sequence name?
Is it like a primary key and different tables are mapped to one sequence 
if I use the same sequence name in different class descriptors?
I'm just interested in what OJB is doing there.

best regards,

Guido

regards,
Armin
* in the repository descriptors, specify the database-generated pk 
fields
as autoincrement='true' and with the sequence-name if you have
autoNaming='false' in the above step

* in the db table schema don't specify the database-generated fields as
identity (whatever the syntax in DB2 is for this) but as a normal non-pk
field (except for NOT NULL which should be present). Also do not connect
the sequences to the pk-fields in the database, this is done by the
sequence manager.
Tom

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