On Oct 17, 2013, at 10:49 AM, Jens Alfke <j...@mooseyard.com> wrote: > > On Oct 17, 2013, at 8:19 AM, Brad Gibbs <bradgi...@mac.com> wrote: > >> Core Data is still a local cache being used by a single user, but instead of >> persisting to the local disk, it’s persisting to the Postgres server. > > But not directly, right? You said there was a Rails app in the middle serving > up a REST API. > >> As for two people making changes to a record simultaneously, it would be >> handled in the same way a Rails web app would handle it. Rails and Postgres >> have been designed for this use case. > > It’s been a while since I used Rails, but the typical way that a > database-driven app manages this is using transactions. Begin transaction, > update rows, end transaction. That makes all the updates atomic.
Yes, but even that does not solve the problem of users overwriting each other's near-simultaneous updates. > But NSIncrementalStore doesn’t have a notion of a transaction, because > CoreData doesn’t care about concurrency, because it’s not multi-user. So if > your Core Data app makes a bunch of changes, they’re going to be sent to the > store, which is going to send them off as individual PUT/POST/DELETE > requests. These can’t be handled atomically by the server; they’re > independent requests. So they can be interleaved with other updates being > made by other clients, causing trouble. Or one of them might fail for some > reason, but then there’s no way to back out to a consistent state; more > trouble. Yep. > I haven’t dug all the way into NSIncrementalStore yet. But the assumption > you’re making is that you can take an architecture that works for a local > single-user database, and transparently make it work over a worldwide network > with lots of users just by [colorful metaphor ahead, not meant to be > insulting!] snipping the wire labeled “SQLite” and soldering it to a wire > labeled “Internet”. This is _exactly_ the kind of thing the “Fallacies Of > Distributed Computing” article warns against … because those fallacies don’t > apply to tightly-bound systems like CoreData+SQLite, and are often ignorable > in LAN-based systems like the typical app-server+db-server setup in a data > center. But on the Internet they will bite you. Yep, lots of issues to "solve"; and none with a single best solution. Been there, done that. Can you tell? -- Scott Ribe scott_r...@elevated-dev.com http://www.elevated-dev.com/ (303) 722-0567 voice _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
