On Thu, Feb 23, 2012 at 19:44, Kevin Grittner <kevin.gritt...@wicourts.gov>wrote:
> One of the problems that Florian was trying to address is that > people often have a need to enforce something with a lot of > similarity to a foreign key, but with more subtle logic than > declarative foreign keys support. One example would be the case > Robert has used in some presentations, where the manager column in > each row in a project table must contain the id of a row in a person > table *which has the project_manager boolean column set to TRUE*. > Short of using the new serializable transaction isolation level in > all related transactions, hand-coding enforcement of this useful > invariant through trigger code (or application code enforced through > some framework) is very tricky. The change to SELECT FOR UPDATE > that Florian was working on would make it pretty straightforward. > I'm not sure what Florian's patch does, but I've been trying to advocate syntax like the following for this exact scenario: foreign key (manager_id, true) references person (id, is_manager) Basically, allow us to use constants instead of field names as part of foreign keys. I have no idea what the implementation aspect of this is, but I need the user aspect of it and don't know the best way to get it.