Example: I have an Cat entity with an catAge attribute. In the data modeler, I configured catAge as int with a max of 100. Then I do this:

[newManagedObject setValue:[NSNumber numberWithInt:125] forKey:@"catAge"];

// Save the context.
NSError *error = nil;
if (![context save:&error]) {
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
}

I'm getting an error in the console, like this:

2010-06-12 11:40:41.947 CatTest[2250:207] Unresolved error Error Domain=NSCocoaErrorDomain Code=1610 UserInfo=0x10164d0 "Operation could not be completed. (Cocoa error 1610.)", {
    NSLocalizedDescription = "Operation could not be completed. (Cocoa error 1610.)";
    NSValidationErrorKey = catAge;
    NSValidationErrorObject = <NSManagedObject: 0x10099f0> (entity: Cat; id: 0x1006a90 <x-coredata:///Cat/t3BCBC34B-8405-4F16-B591-BE804B6811562> ; data: {
    catAge = 125;
    catName = "No Name";
});
    NSValidationErrorPredicate = SELF <= 100;
    NSValidationErrorValue = 125;
}

Well, so I have an validation error. But the odd thing is, that it seems the MOC is broken after this. If I just tap "add" to add another invalid Cat object and save that, I'm getting this:

2010-06-12 11:45:13.857 CatTest[2250:207] Unresolved error Error Domain=NSCocoaErrorDomain Code=1560 UserInfo=0x1232170 "Operation could not be completed. (Cocoa error 1560.)", {
    NSDetailedErrors =     (
        Error Domain=NSCocoaErrorDomain Code=1610 UserInfo=0x1215f00 "Operation could not be completed. (Cocoa error 1610.)",
        Error Domain=NSCocoaErrorDomain Code=1610 UserInfo=0x1209fc0 "Operation could not be completed. (Cocoa error 1610.)"
    );
}

That seems to report two errors now. BUT: When I try to delete now an valid, existing object from the table view (using the default core data template in a navigation-based app), then the app crashes! All I get in the console is:

2010-06-12 11:47:18.931 CatTest[2250:207] Unresolved error Error Domain=NSCocoaErrorDomain Code=1560 UserInfo=0x123eb30 "Operation could not be completed. (Cocoa error 1560.)", {
    NSDetailedErrors =     (
        Error Domain=NSCocoaErrorDomain Code=1610 UserInfo=0x1217010 "Operation could not be completed. (Cocoa error 1610.)",
        Error Domain=NSCocoaErrorDomain Code=1610 UserInfo=0x123ea80 "Operation could not be completed. (Cocoa error 1610.)"
    );
}

...so no idea where or why it crashes, but it does. So the question is, what are the neccessary steps to take when there's an validation error?