RestKit addFetchRequestBlock causes objects not to be mapped - ios

Question

I have the following fetch request block set up to deal with deletion of orphaned objects:
[objectManager addFetchRequestBlock:^NSFetchRequest *(NSURL *URL) {
RKPathMatcher *pathMatcher = [RKPathMatcher pathMatcherWithPattern:API_GET_ACTIVE_RIDES];
NSString * relativePath = [URL relativePath];
NSDictionary *argsDict = nil;
BOOL match = [pathMatcher matchesPath:relativePath tokenizeQueryStrings:NO parsedArguments:&argsDict];
if (match) {
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:#"Ride"];
return fetchRequest;
}
return nil;
}];
Since I need to allow users to log out and log back in, I clear all data from core data using the following:
+ (void) clearUserData {
NSError * error = nil;
[[RKManagedObjectStore defaultStore] resetPersistentStores:&error];
if(error != nil){
[WRUtilities criticalError:error];
return;
}
}
However, if I log out and log back into my app, objects that were loaded the first time I logged in are not loaded from the server. Using RestKit logging, I can see that the request goes out and returns the correct data from the server, but mapping appears to be completely skipped, causing no objects to be (re)inserted into core data.
If I remove my fetch request block, everything works as I would expect - clearUserData removes all data, and upload login the data is re-queried from the server and reloaded into core data.
My question is two fold. What do I need to change to get the expected behavior of successfully reloading data, and why does the fetch request block, which I understand to be only for deleting orphaned objects, have an effect on this scenario?
I've seen this before and just removed the fetch request block, but I would prefer to use this feature rather than skip it because of this problem.

Answer 1

I had this exact problem and managed to find a solution. Essentially the code below will only return a fetch request if there are existing items held in CoreData. The problem with returning it all the time means that RestKit will delete the items you get from the server the first time. The idea here is to return nil if there are no items currently held in CoreData. Not sure if this is the way RestKit would recommend, but it worked for me.
RKObjectManager *sharedManager = [RKObjectManager sharedManager];
[sharedManager addFetchRequestBlock:^NSFetchRequest *(NSURL *URL) {
RKPathMatcher *userPathMatcher = [RKPathMatcher pathMatcherWithPattern:#"my/api/path"];
BOOL match = [userPathMatcher matchesPath:[URL relativePath] tokenizeQueryStrings:NO parsedArguments:nil];
if(match) {
// lets first check if we have anything in coredata
NSString * const entityName = NSStringFromClass([MyCoreDataEntity class]);
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:entityName];
NSError *error = nil;
NSManagedObjectContext *managedObjectContext = [RKManagedObjectStore defaultStore].mainQueueManagedObjectContext;
NSArray *results = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
if(error) {
// this shouldn't happen, but if something went wrong querying CoreData
// lets just save the new ones
NSLog(#"error %#", error);
return nil;
}
if([results count] > 0) {
// if we already have something saved, lets delete 'em and save
// the new ones
return [NSFetchRequest fetchRequestWithEntityName:entityName];
}
else {
// if we don't have something saved, lets save them
// (e.g. first time after login after we cleared everything on logout)
return nil;
}
}
return nil;
}];
Hope that helps!