iPhone Core Data “Production” Error Handling

Question

I\'ve seen in the example code supplied by Apple references to how you should handle Core Data errors. I.e:

NSError *error = nil;
if (![context save:&err         


        

Answer 1

I've made a Swift version of the useful answer of @JohannesFahrenkrug which can be useful :

public func displayValidationError(anError:NSError?) -> String {
    if anError != nil && anError!.domain.compare("NSCocoaErrorDomain") == .OrderedSame {
        var messages:String = "Reason(s):\n"
        var errors = [AnyObject]()
        if (anError!.code == NSValidationMultipleErrorsError) {
            errors = anError!.userInfo[NSDetailedErrorsKey] as! [AnyObject]
        } else {
            errors = [AnyObject]()
            errors.append(anError!)
        }
        if (errors.count > 0) {
            for error in errors {
                if (error as? NSError)!.userInfo.keys.contains("conflictList") {
                    messages =  messages.stringByAppendingString("Generic merge conflict. see details : \(error)")
                }
                else
                {
                    let entityName = "\(((error as? NSError)!.userInfo["NSValidationErrorObject"] as! NSManagedObject).entity.name)"
                    let attributeName = "\((error as? NSError)!.userInfo["NSValidationErrorKey"])"
                    var msg = ""
                    switch (error.code) {
                    case NSManagedObjectValidationError:
                        msg = "Generic validation error.";
                        break;
                    case NSValidationMissingMandatoryPropertyError:
                        msg = String(format:"The attribute '%@' mustn't be empty.", attributeName)
                        break;
                    case NSValidationRelationshipLacksMinimumCountError:
                        msg = String(format:"The relationship '%@' doesn't have enough entries.", attributeName)
                        break;
                    case NSValidationRelationshipExceedsMaximumCountError:
                        msg = String(format:"The relationship '%@' has too many entries.", attributeName)
                        break;
                    case NSValidationRelationshipDeniedDeleteError:
                        msg = String(format:"To delete, the relationship '%@' must be empty.", attributeName)
                        break;
                    case NSValidationNumberTooLargeError:
                        msg = String(format:"The number of the attribute '%@' is too large.", attributeName)
                        break;
                    case NSValidationNumberTooSmallError:
                        msg = String(format:"The number of the attribute '%@' is too small.", attributeName)
                        break;
                    case NSValidationDateTooLateError:
                        msg = String(format:"The date of the attribute '%@' is too late.", attributeName)
                        break;
                    case NSValidationDateTooSoonError:
                        msg = String(format:"The date of the attribute '%@' is too soon.", attributeName)
                        break;
                    case NSValidationInvalidDateError:
                        msg = String(format:"The date of the attribute '%@' is invalid.", attributeName)
                        break;
                    case NSValidationStringTooLongError:
                        msg = String(format:"The text of the attribute '%@' is too long.", attributeName)
                        break;
                    case NSValidationStringTooShortError:
                        msg = String(format:"The text of the attribute '%@' is too short.", attributeName)
                        break;
                    case NSValidationStringPatternMatchingError:
                        msg = String(format:"The text of the attribute '%@' doesn't match the required pattern.", attributeName)
                        break;
                    default:
                        msg = String(format:"Unknown error (code %i).", error.code) as String
                        break;
                    }

                    messages = messages.stringByAppendingString("\(entityName).\(attributeName):\(msg)\n")
                }
            }
        }
        return messages
    }
    return "no error"
}`