Restkit truncate db before core data mapping - core-data

Question

i'm using restkit to map a json with core data
i need to call a routine every time the user launch the app.
if the server has updated data to send, i need to download them, truncate my table and insert the data in the table, if the server sends me nothing i don't have to do nothing.
obviously i want to truncate my current data only when i'm sure that new data has been downloaded, not before
how can I achieve this?
this is my code:
NSURL *endpoint = [NSURL URLWithString:kBaseURL];
RKObjectManager* objectManager = [RKObjectManager managerWithBaseURL:endpoint];
[objectManager.HTTPClient setAuthorizationHeaderWithToken:#"username:my-token-12345"];
objectManager.managedObjectStore = [RKManagedObjectStore defaultStore];
[RKObjectManager setSharedManager:objectManager];
RKEntityMapping *entityMapping = [RKEntityMapping mappingForEntityForName:#"Medic" inManagedObjectStore:objectManager.managedObjectStore];
[entityMapping addAttributeMappingsFromDictionary:#{
#"identifier": #"identifier",
#"name": #"name",
#"surname": #"surname",
#"personalAddress": #"personalAddress",
#"hospital": #"hospital",
#"hospitalAddress": #"hospitalAddress",
#"oldDigitalAgreement": #"oldDigitalAgreement",
#"oldPaperAgreement": #"oldPaperAgreement"}];
entityMapping.identificationAttributes = #[#"identifier"];
RKResponseDescriptor *responseDescriptor = [RKResponseDescriptor
responseDescriptorWithMapping:entityMapping
method:RKRequestMethodAny
pathPattern:nil
keyPath:nil
statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];
[objectManager addResponseDescriptor:responseDescriptor];
[[RKObjectManager sharedManager] getObjectsAtPath:kregistryURL
parameters:nil
success:^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) {
// done
}
failure:^(RKObjectRequestOperation *operation, NSError *error) {
UIAlertView * alertView = [[UIAlertView alloc]initWithTitle:NSLocalizedString(#"attention", nil) message:NSLocalizedString(#"communication.genericerror.title", nil) delegate:nil cancelButtonTitle:nil otherButtonTitles:#"Ok", nil];
[alertView show];
}
];
solution after Wain answer
[objectManager addFetchRequestBlock:^NSFetchRequest *(NSURL *URL) {
RKPathMatcher* pathMatcher = [RKPathMatcher pathMatcherWithPattern:kregistryURL];
NSDictionary *dic = nil;
if ([pathMatcher matchesPath:[URL relativePath] tokenizeQueryStrings:YES parsedArguments:&dic]) {
NSFetchRequest *fetchRequest = [NSFetchRequest new];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Medic"
inManagedObjectContext: [RKManagedObjectStore defaultStore].mainQueueManagedObjectContext];
fetchRequest.entity = entity;
return fetchRequest;
} else
return nil;
}];

Answer 1

Your problem is
if the server sends me nothing, i don't have to do _any_thing
and I'm guessing the server still sends a 200 response rather than a special status code (it should be 304 ‘Not Modified’). Because if you didn't have that requirement you could use a deletion fetch request block (which is the correct solution).
As it stands, you will likely have to do the deletion yourself by fetching the existing items from the data store and iterating over them, checking if the item is in the mapping results provided to you in the success block and, if not, deleting it from the context...