primary key generation
Jef Kelly
Greenhorn
Posts: 8
posted 12 years ago
Ok, I know this isn't on the exam, but I want to practice coding a few beans before I take the test, and I ran into a bit of a mire right out of the gate.
In the real world, is there an accepted or standard way of generating primary keys for entity beans?
Assuming a numeric PK...I've considered having a single go-to bean that reads the max value of the PK field in the database and then increments and doles them out. But if I do this as a bean, then every create() called on that bean's home is going to produce a bean that generates duplicates of every other bean in the pool! (more or less)
Static non-final field/method would seem to be an obvious bet, but they're disallowed.
Helper class? Vendor-specific dealie that I don't know about?
This seems like such a basic issue, but I haven't found any posts about it here....
In the real world, is there an accepted or standard way of generating primary keys for entity beans?
Assuming a numeric PK...I've considered having a single go-to bean that reads the max value of the PK field in the database and then increments and doles them out. But if I do this as a bean, then every create() called on that bean's home is going to produce a bean that generates duplicates of every other bean in the pool! (more or less)
Static non-final field/method would seem to be an obvious bet, but they're disallowed.
Helper class? Vendor-specific dealie that I don't know about?
This seems like such a basic issue, but I haven't found any posts about it here....
Jason Hunt
Ranch Hand
Posts: 51
posted 12 years ago
You can create a db table to hold the key for each bean and create a entity bean mapping to this table, every time you get the pk, it increase the value.
SCJP, SCWCD, SCBCD, SCDJWS, OCA9i,<br />IBM Certified WAS5.0 Admin<br />IBM Certified Solution Developer - WebSphere Studio 5.0<br />IBM Certified Solution Developer - XML and related Technologies
Olexiy Prokhorenko
Ranch Hand
Posts: 97
posted 12 years ago
can you explain a bit more in details?
may be some example, if possible?
i am not sure that i understood. :-(
may be some example, if possible?
i am not sure that i understood. :-(
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Jef Kelly
Greenhorn
Posts: 8
posted 12 years ago
Thanks, Jason. I must admit it took me a few seconds before I slapped my forehead and said "Of course!"
I set up a PRIMARY_KEY table that looks (currently) like this:
PK_PK, EMPLOYEE_PK
1 207
I'm now creating an entity with only one business method, getEmployeePK(). It returns the value of EMPLOYEE_PK and then increments EMPLOYEE_PK. The bean has create methods, and ejbRemove calls setRollbackOnly to keep anyone from removing this one and only row. It seems like a good idea to make the trans-attribute mandatory to make sure that this whole process is part of the calling transaction.
Sound about right?
Is this sort of approach..."industry standard?"
I set up a PRIMARY_KEY table that looks (currently) like this:
PK_PK, EMPLOYEE_PK
1 207
I'm now creating an entity with only one business method, getEmployeePK(). It returns the value of EMPLOYEE_PK and then increments EMPLOYEE_PK. The bean has create methods, and ejbRemove calls setRollbackOnly to keep anyone from removing this one and only row. It seems like a good idea to make the trans-attribute mandatory to make sure that this whole process is part of the calling transaction.
Sound about right?
Is this sort of approach..."industry standard?"
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