Re: foreign key from array element

Hi Chris,

   thank you very much for taking the time to read the article and get into the features proposed with our patch.

I agree with you that this feature won't (and probably shouldn't) change modelling approaches in the majority of the cases. But will bring new opportunities, therefore make PostgreSQL even more versatile. I still believe that in some cases - not just indistinctively - aggregation in object oriented modelling can definitely be logically modelled using arrays, with referential integrity guaranteed by this feature.

However, after thinking about the feature overnight, I can see a
number of use cases for it, ranging from recording something like race
results (where update contention is definitionally not an issue
because the record of an event aren't supposed to change) to sanity
checks in materialized views, and there are probably additional uses
that are not apparent yet.

I totally agree with you. This is exactly what we (as a community) need to do now as far as this feature is concerned. We need to have a larger use base and from there fully understand what the community needs. For instance, for 9.2 we had already developed actions on update and delete operations - assuming generic use cases. We have preferred for now to take out that part and start with a simpler patch where actions are forbidden. Through community feedback we found a name for the feature that was commonly accepted (we had called them EACH FOREIGN KEYS last year), and came up with an easy to understand syntax (and a better naming). It was important not to go too far down an unexplored territory. :)