Hi Paul, For cases like this, the database is the right, and only, place to guarantee this.
Chuck From: Webobjects-dev <webobjects-dev-bounces+chill=gevityinc....@lists.apple.com> on behalf of Paul Hoadley <pa...@logicsquad.net> Date: Monday, August 14, 2017 at 7:11 PM To: WebObjectsDev <webobjects-dev@lists.apple.com> Subject: Enforcing a maximum cardinality on a many-to-many relationship Hello, I have EOs Job and Worker. Job.workers is a many-to-many relationship to Worker, set up in the usual way, so there’s a JobWorker join table. Job.maxWorkers is a mandatory Integer attribute whose value will be 1 or greater. I need to enforce a business rule such that Job.workers.count can never exceed Job.maxWorkers. It’s sufficient that this is enforced at save-time: if a particular in-memory Job has addToWorkersRelationship() called on it too many times, I’m not too bothered, but it can’t be saved that way. Further, it needs to be robust in the presence of multiple EOF stacks. (And although we use JGroups synchronisation in deployment, assume that we don’t. The sync may not happen fast enough.) To me this sounds like a problem for database triggers: reject an insert on JobWorker that would cause Job.workers.count to exceed Job.maxWorkers for the referenced Job. Before I launch into that, though, does anyone know of (or can anyone think of) a robust EOF-only solution to this problem? -- Paul Hoadley https://logicsquad.net/ https://www.linkedin.com/company/logic-squad/
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