>>I [assign a PK] in the Record Validation Rule; if the key field is empty, I determine an appropriate value for the key and REPLACE the key with it.
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>Interesting. What would you say is the benefit to doing it then, instead of making the key determination the default value?
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>A drawback that I can see is that you don't find out what your PK is until TableUpdate(), and I have one app where I add both parent and child records at the same time. The child needs to know the parent's PK right away.

If the PK won´t ever be seen by the user, then you could generate it anytime. Anyway, I also have programs with parent/child records, and after generating the PK for the parent I go and REPLACE its value in the children.