Generate one Id column included in composite Primary Keys in JPA, while one Id starts from 1 when the other Id column changes

Asked Jan 31 '23 at 17:19

Active Jan 31 '23 at 17:19

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The entity A has an OneToMany relation with the entity B. I would like to use a composite primary key for the entity B, where one of the columns is the same as the the primary key of the entity A and the second column should be generated. How can the second column be started from 1 whenever the the other involving column within the composite primary key changes?

I use Oracle data bank and could not find any solution.

Thanks in advance!

asked Jan 31 '23 at 17:19

Mahtab Makaremi

So you want a sequence/count that is per A? There isn't a DB sequence, so such functionality isn't included in JPA, but you can write your own in any pre-persist event on B to count all Bs associated with that A (or return the max ID value for those Bs) and use the next one. Or use a database stored proc to do the insert and set the ID for you. – Chris Jan 31 '23 at 18:47

Generate one Id column included in composite Primary Keys in JPA, while one Id starts from 1 when the other Id column changes

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