NSFetchedResultsController provides a lot of nice stuff free when working with tableViews. I also understand that storing fetch requests in the model is good form. Can I use both of these together for super core data goodness? If so, how so?
This example from Mr. Zarra's excellent book shows the template returning an array and I've failed in my attempts to get a fetchedResultsController back.
- (NSArray*)retrieveBigMeals {
NSManagedObjectContext *moc = [self managedObjectContext];
NSManagedObjectModel *mom = [self managedObjectModel];
NSFetchRequest *request = [mom fetchRequestTemplateForName:#"bigMeals"];
NSError *error = nil;
NSArray *result = [moc executeFetchRequest:request error:&error];
if (error) {
[NSApp presentError:error]; return nil;
} return result;
Just use the ios navigation based application template with core data. They already have the code for using NSFetchedResultController there.
Related
I am a VERY new beginner to Core Data and I have recently been trying to read and write data. I created an entity named "Person" with the entities "name" and "age". I also have a textfield name "personName" and a textfield named "personAge".
- (IBAction)readData:(id)sender
{
NSNumber *ageNum = [NSNumber numberWithInteger:personAge.text.integerValue];
Person *newPerson = [NSEntityDescription insertNewObjectForEntityForName:#"Person" inManagedObjectContext:managedObjectContext];
newPerson.name = personName.text;
newPerson.age = ageNum;
NSLog(#"Person %# name is %#", personName.text, ageNum);
}
When I load the app, all i get is SIGABRT. Even when all I put in the method is
Person *newPerson = [NSEntityDescription insertNewObjectForEntityForName:#"Person" inManagedObjectContext:managedObjectContext];
All help is appreciated.
For Adding values to the core data you can do so:-
- (IBAction)save:(id)sender {
NSManagedObjectContext *context = [self managedObjectContext];
// Create a new managed object
NSManagedObject *person = [NSEntityDescription insertNewObjectForEntityForName:#"Person" inManagedObjectContext:context];
[person setValue:self.personName.text forKey:#"name"];
[person setValue:self.personAge.text forKey:#"age"];
NSError *error = nil;
// Save the object to persistent store
if (![context save:&error]) {
NSLog(#"Can't Save! %# %#", error, [error localizedDescription]);
}
}
For fetching the values from core data:-
NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:#"Person"];
self.personValues = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
here personValues is a NSMutableArray.
For better understanding about these please go through this link.
http://www.appcoda.com/introduction-to-core-data/
Hope this will help you out.
If you are very new to Core Data, try using the MagicalRecord library which provides a series of helper categories for dealing with a lot of the boiler plate setup of Core Data.
Which brings me to the question you are asking: are you sure your Core Data stack is being setup correctly? Check to make sure your Managed Object Context is valid along with a proper Persistent Store Coordinator.
Best thing to do: put a breakpoint during the Core Data stack setup and step through it making sure everything is setup properly. Or install MagicalRecord and do one method call to [MagicalRecord setupAutomigratingCoreDataStack]...
Regarding one answer in another post: is that use executeFetchRequest in a loop a bad practice? I saw that usage in Stanford CS193p project "Photomania" (click link to download project). The relevant code is below:
The [FlickrFetcher recentGeoreferencedPhotos] is used to fetch photos from Flickr API, which happens in a background thread. But the loop that execute fetch request happens in main thread.
- (void)fetchFlickrDataIntoDocument:(UIManagedDocument *)document
{
dispatch_queue_t fetchQ = dispatch_queue_create("Flickr fetcher", NULL);
dispatch_async(fetchQ, ^{
NSArray *photos = [FlickrFetcher recentGeoreferencedPhotos];
// perform in the NSMOC's safe thread (main thread)
[document.managedObjectContext performBlock:^{
for (NSDictionary *flickrInfo in photos) {
// This is the method that will call executeFetchRequest
[Photo photoWithFlickrInfo:flickrInfo inManagedObjectContext:document.managedObjectContext];
}
[document saveToURL:document.fileURL forSaveOperation:UIDocumentSaveForOverwriting completionHandler:NULL];
}];
});
dispatch_release(fetchQ);
}
Here is the factory method that first try to fetch objects from context (according to a pass-in object, which is fetched from flickr API). If result is nil, insert that object into context.
+ (Photo *)photoWithFlickrInfo:(NSDictionary *)flickrInfo
inManagedObjectContext:(NSManagedObjectContext *)context
{
Photo *photo = nil;
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:#"Photo"];
request.predicate = [NSPredicate predicateWithFormat:#"unique = %#", [flickrInfo objectForKey:FLICKR_PHOTO_ID]];
NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:#"title" ascending:YES];
request.sortDescriptors = [NSArray arrayWithObject:sortDescriptor];
NSError *error = nil;
NSArray *matches = [context executeFetchRequest:request error:&error];
if (!matches || ([matches count] > 1)) {
// handle error
} else if ([matches count] == 0) {
photo = [NSEntityDescription insertNewObjectForEntityForName:#"Photo" inManagedObjectContext:context];
photo.unique = [flickrInfo objectForKey:FLICKR_PHOTO_ID];
photo.title = [flickrInfo objectForKey:FLICKR_PHOTO_TITLE];
photo.subtitle = [flickrInfo valueForKeyPath:FLICKR_PHOTO_DESCRIPTION];
photo.imageURL = [[FlickrFetcher urlForPhoto:flickrInfo format:FlickrPhotoFormatLarge] absoluteString];
photo.whoTook = [Photographer photographerWithName:[flickrInfo objectForKey:FLICKR_PHOTO_OWNER] inManagedObjectContext:context];
} else {
photo = [matches lastObject];
}
return photo;
}
I already replied in your question Core data: executeFetchRequest vs performFetch.
Here what I wrote:
Executing the request within a loop could have impact on performances
but I would not be worried on that. Under the hood Core Data maintains
a sort of cache mechanism. Every time you perform a request, if data
are not in the cache, Core Data executes a round trip on your store
(e.g. sql file) and populate the cache with the objects it has
retrieved. If you perform the same query, the round trip will not
performed again due to the cache mechanism. Anyway, you could avoid to
execute a request within the run loop, simply moving that request
outside the loop.
In this case the request within the for loop is ok since you need to find the possible matches for the current (NSDictionary *)flickrInfo.
An alternative way, it could be to move the request outside the method
+ (Photo *)photoWithFlickrInfo:(NSDictionary *)flickrInfo
inManagedObjectContext:(NSManagedObjectContext *)context;
So for example, modify this method to accomodate a NSArray of results like:
+ (Photo *)photoWithFlickrInfo:(NSDictionary *)flickrInfo photoResults:(NSArray*)results
inManagedObjectContext:(NSManagedObjectContext *)context;
Replace the first snippet of code with the following
- (void)fetchFlickrDataIntoDocument:(UIManagedDocument *)document
{
dispatch_queue_t fetchQ = dispatch_queue_create("Flickr fetcher", NULL);
dispatch_async(fetchQ, ^{
NSArray *photos = [FlickrFetcher recentGeoreferencedPhotos];
// perform in the NSMOC's safe thread (main thread)
[document.managedObjectContext performBlock:^{
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:#"Photo"];
NSArray *results = [context executeFetchRequest:request error:&error];
for (NSDictionary *flickrInfo in photos) {
// This is the method that will call executeFetchRequest
[Photo photoWithFlickrInfo:flickrInfo photoResult:results inManagedObjectContext:document.managedObjectContext];
}
[document saveToURL:document.fileURL forSaveOperation:UIDocumentSaveForOverwriting completionHandler:NULL];
}];
});
dispatch_release(fetchQ);
}
In this case through the request you retrieve all the stored photos. The array (of managed objects) is passed to +(Photo*)photoWithFlickrInfo:photoResults:inManagedObjectContext:.
Now within +(Photo *)photoWithFlickrInfo:photoResults:inManagedObjectContext: you need to set a predicate for results that find the possible candidate based on [flickrInfo objectForKey:FLICKR_PHOTO_ID];. The motivation is quite simple: you have move the request outside the loop and now you need to retrieve the specific one. So, for example, you could do like:
+ (Photo *)photoWithFlickrInfo:(NSDictionary *)flickrInfo photoResults:(NSArray*)results
inManagedObjectContext:(NSManagedObjectContext *)context
{
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"unique == %#", [flickrInfo objectForKey:FLICKR_PHOTO_ID]];
NSArray* filteredPredicate = [results filterUsingPredicate:predicate];
// now filteredPredicate is the same as matches in the second snippet of your code.
// do the other code here..
}
Summarizing
Both approaches are valid. By means of them you can retrieve a photo already created or create a new one.
That's why loop is unavoidable. Am I wrong on this?
No, since you can try to follow my approach but the approach provided in Standford Course has a greater performance than the one I posted. I didn't made any performance test but if you are interested in you can do it yourself and analyze results by Instruments.
Simple tip
A simple change in the Standford code could be to perform Core Data operation in background preventing the main thread to be blocked. This approach could be useful if you have a lot of data. If data is minimal leave it as is.
I am using a WCF service in my app.When the app is run for the first time on the iPad,I want it to call a WCF service and display the result in a UITableView.Alongwith displaying the data in UITableView,i want to store the data in Core Data so when the user is "offline"(not connected to wifi)the data will be displayed from the Core Data.The AppDelegate.m looks like this:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
if (![defaults objectForKey:#"firstRun"])
{
self.firstRun = TRUE;
[defaults setObject:[NSDate date] forKey:#"firstRun"];
}
else
{
self.firstRun = FALSE;//flag does exist so this ISNT the first run
}
[[NSUserDefaults standardUserDefaults] synchronize];
}
The code in UITableView looks like this:
- (void)viewDidLoad
{
[super viewDidLoad];
[my_table setDataSource:self];
[my_table setDelegate:self];
AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
if (appDelegate.firstRun){
NSLog(#"IS FIRST RUN");
EDViPadDocSyncService *service = [[EDViPadDocSyncService alloc]init];
[service getAllCategories:self action:#selector(handleGetAllCategories:)];
}
else
{
NSLog(#"NOT FIRST RUN");
NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription
entityForName:#"Categories" inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
NSError *errormsg;
self.allCats = [managedObjectContext executeFetchRequest:fetchRequest error:&errormsg];
NSLog(#"allCATS=%#",self.allCats);
self.title = #"Categories";
}
}
-(void)handleGetAllCategories:(id)value
{
if([value isKindOfClass:[NSError class]])
{
NSLog(#"This is an error %#",value);
return;
}
if([value isKindOfClass:[SoapFault class]])
{
NSLog(#"this is a soap fault %#",value);
return;
}
NSMutableArray *result = (NSMutableArray*)value;
NSMutableArray *categoryList = [[NSMutableArray alloc] init];
NSMutableArray *docCount = [[NSMutableArray alloc]init];
NSMutableArray *catIdList = [[NSMutableArray alloc]init];
self.myData = [[NSMutableArray array] init];
self.myDocCount = [[NSMutableArray array]init];
self.catId = [[NSMutableArray array]init];
for (int i = 0; i < [result count]; i++)
{
EDVCategory *catObj = [[EDVCategory alloc]init];
catObj = [result objectAtIndex:i];
[categoryList addObject:[catObj categoryName]];
[docCount addObject:[NSNumber numberWithInt:[catObj docCount]]];
[catIdList addObject:[NSNumber numberWithInt:[catObj categoryId]]];
}
self.myData = categoryList;
self.myDocCount = docCount;
self.catId = catIdList;
[my_table reloadData];
/*store data in Core Data - START*/
NSManagedObjectContext *context = [self managedObjectContext];
NSManagedObject *newCategory;
for(int j=0;j<[result count];j++)
{
newCategory = [NSEntityDescription insertNewObjectForEntityForName:#"Categories" inManagedObjectContext:context];
/*HOW TO STORE DATA FOR THE "CATEGORIES" OBJECT IN CORE DATA*/
}
/*store data in Core Data - END*/
}
I am not able to figure out how to store the data received from the wcf service to the core data object directly.I know how to store it from a text box on the screen to a core data object.eg.:-
coreDataAppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
NSManagedObjectContext *context = [appDelegate managedObjectContext];
NSManagedObject *newContact;
newCat = [NSEntityDescription insertNewObjectForEntityForName:#"Categories" inManagedObjectContext:context];
[newCat setValue:name.text forKey:#"name"];
name.text = #"";
[context save:&error];
But this doesn't help in my case.Any help is appreciated.
You are mixing networking and UI code. It is a recipe for unmaintainable code.
Your UI should be looking at Core Data and only Core Data to display its data.
Separately, and asynchronously you should be requesting data from WCF and pushing it into Core Data.
Your UI does not need to care about first run vs. subsequent run. It just looks at Core Data via a NSFetchedResultsController.
Your network code is the only part that cares about new vs. update.
Update 1
how can I achieve this? When the app is running and connected to WiFi,it has to get the latest data from the WCF service.
NSURLConnection can do async requests built-in. I generally recommend writing your networking code as NSOperation subclasses and then put them into a queue.
It appears that WCF can return XML and takes standard HTTP requests. Therefore you can write NSOperation subclasses that build your request, send it to the server and wait for a reply. When the reply comes you parse the XML and insert it into Core Data. When you save the Core Data NSManagedObjectContext your NSFetchedResultsController instances will automatically fire and allow you to update your UI.
I have several code samples that perform these feats although they are written for JSON responses as opposed to XML responses. It would not be difficult to take those examples and alter them to your needs.
You can start with this stackoverflow question and its response.
To store the data into the attributes of your NSManagedObject, simply set the values using KVC:
EDVCategory *catObject = [result objectAtIndex:j];
[newCategory setValue:[catObject categoryName] forKey#"categoryName"];
[newCategory setValue:[catObject docCount] forKey#"docCount"];
[newCategory setValue:[catObject categoryID] forKey#"categoryID"];
// after the loop
[context save:&nil];
I have come across an interesting conundrum (of course, I could just being doing something horribly wrong).
I would like an NSTokenField to "represent" a relationship in a Core Data Application. The premise is such: You click on a Note from a TableView (loaded from the Notes Array Controller). The token field is then bound (through "value") to the Notes Array Controller selection.Tags. Tags is a to-many relationship on the entity Notes.
Obviously, an NSTokenField will not accept the NSSet that the Array Controller Provides it. To get around this, I subclassed NSTokenFieldCell and overrode its objectValue and setObjectValue: methods. I thought that I could simply translate the NSSet that was being provided to the NSArray that the NSTokenFieldCell expected. (Note: I originally tried overriding these methods on a NSTokenField subclass; however, they were not being called.)
So, I came up with said code:
- (void)setObjectValue:(NSSet*)object {
tagsList = [object copy];
NSMutableArray *displayList = [[NSMutableArray alloc] init];
for (id newObject in tagsList) {
[displayList addObject:[newObject valueForKey:#"Name"]];
}
[super setObjectValue:displayList];
}
- (id)objectValue {
NSArray *displayList = [super objectValue];
NSEntityDescription *tagEntity = [NSEntityDescription
entityForName:#"Tag"
inManagedObjectContext:[appDelegate
managedObjectContext]];
NSMutableSet *returnValue = [[NSMutableSet alloc] init];
for (NSString *token in displayList) {
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
[request setEntity:tagEntity];
NSPredicate *predicate = [NSPredicate predicateWithFormat:
#"Name == %#", token];
[request setPredicate:predicate];
NSError *error;
NSArray *results = [[appDelegate managedObjectContext] executeFetchRequest:request error:&error];
if (results == nil) {
NSManagedObject *object = [NSEntityDescription insertNewObjectForEntityForName:#"Tag" inManagedObjectContext:[appDelegate managedObjectContext]];
[object setValue:token forKey:#"Name"];
[returnValue addObject:object];
} else {
[returnValue addObject:[results objectAtIndex:0]];
}
}
return returnValue;
}
It crashes. :( And, surprisingly it crashes on the line that calls [super objectValue]. It gives me the error:
-[NSConcreteAttributedString countByEnumeratingWithState:objects:count:]: unrecognized selector sent to instance ...
Sigh. The sad thing is that when I go into the Core Data XML file and give the Note a Tag, it displays correctly, and [super setObjectValue:] is passed an array of strings. However, as soon as I enter something else and mouse away, I get the error.
I am not sure what to do about this. Can anyone spot anything horribly wrong with this? Thanks.
UPDATE:
If it makes a difference, I do not have a delegate configured for the TokenField.
In typical SO fashion, I found the answer to my own question. It was silly to begin with. I simply needed another ArrayController bound to the Notes selection.Tags set. Then, I bound the NSTokenField to the ArrangedObjects of that Controller, implemented some delegate methods. Boom. Simple.
Silly me.
I'm working on an iPhone app that gets a number of objects from a database. I'd like to store these using Core Data, but I'm having problems with my relationships.
A Detail contains any number of POIs (points of interest). When I fetch a set of POI's from the server, they contain a detail ID. In order to associate the POI with the Detail (by ID), my process is as follows:
Query the ManagedObjectContext for the detailID.
If that detail exists, add the poi to it.
If it doesn't, create the detail (it has other properties that will be populated lazily).
The problem with this is performance. Performing constant queries to Core Data is slow, to the point where adding a list of 150 POI's takes a minute thanks to the multiple relationships involved.
In my old model, before Core Data (various NSDictionary cache objects) this process was super fast (look up a key in a dictionary, then create it if it doesn't exist)
I have more relationships than just this one, but pretty much every one has to do this check (some are many to many, and they have a real problem).
Does anyone have any suggestions for how I can help this? I could perform fewer queries (by searching for a number of different ID's), but I'm not sure how much this will help.
Some code:
POI *poi = [NSEntityDescription
insertNewObjectForEntityForName:#"POI"
inManagedObjectContext:[(AppDelegate*)[UIApplication sharedApplication].delegate managedObjectContext]];
poi.POIid = [attributeDict objectForKey:kAttributeID];
poi.detailId = [attributeDict objectForKey:kAttributeDetailID];
Detail *detail = [self findDetailForID:poi.POIid];
if(detail == nil)
{
detail = [NSEntityDescription
insertNewObjectForEntityForName:#"Detail"
inManagedObjectContext:[(AppDelegate*)[UIApplication sharedApplication].delegate managedObjectContext]];
detail.title = poi.POIid;
detail.subtitle = #"";
detail.detailType = [attributeDict objectForKey:kAttributeType];
}
-(Detail*)findDetailForID:(NSString*)detailID {
NSManagedObjectContext *moc = [[UIApplication sharedApplication].delegate managedObjectContext];
NSEntityDescription *entityDescription = [NSEntityDescription
entityForName:#"Detail" inManagedObjectContext:moc];
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
[request setEntity:entityDescription];
NSPredicate *predicate = [NSPredicate predicateWithFormat:
#"detailid == %#", detailID];
[request setPredicate:predicate];
NSLog(#"%#", [predicate description]);
NSError *error;
NSArray *array = [moc executeFetchRequest:request error:&error];
if (array == nil || [array count] != 1)
{
// Deal with error...
return nil;
}
return [array objectAtIndex:0];
}
Check out the section titled "Batch Faulting" on the page titled "Core Data Performance" in Xcode's Core Data Programming Guide that Norman linked to in his answer.
Only fetching those managedObjects whose ids are IN a collection (NSSet, NSArray, NSDictionary) of ids of the objects returned by the server may be even more efficient.
NSSet *oids = [[NSSet alloc] initWithObjects:#"oid1", #"oid2", ..., nil];
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"oid IN %#", oids];
[oids release];
UPDATE: I worked this tip into a solution for the acani usersView. Basically, after downloading a JSON response of users, the iPhone uses the popular open source JSON framework to parse the response into an NSArray of NSDictionary objects, each representing a user. Then, it makes an NSArray of their uids and does a batch fetch on Core Data to see if any of them already exist on the iPhone. If not, it inserts it. If so, it updates the ones that do exist only if their updated attribute is older than that of the one from the server.
I've gotten all this to work really well, thanks to Norman, who put me on the right path. I'll post my helper class here for others.
Basically, my helper class will look up if an NSManagedObject exists for some ID, and can create it for some ID. This executes quickly enough for me, with 1,000 find/create operations taking around 2 seconds on my iPhone (I also did a few other things there, pure find/create is likely faster).
It does this by caching a dictionary of all the NSManagedObjects, and checking that cache rather than executing a new NSFetchRequest.
A couple of modifications that could help things speed up even further:
1. Get only selected properties for the NSManagedObjects
2. Only get the identifier property for the NSManagedObject into a dictionary, instead of the whole object.
In my performance testing, the single query wasn't the slow part (but with only 1,000 items, I'd expect it to be fast). The slow part was the creation of the items.
#import "CoreDataUniquer.h"
#implementation CoreDataUniquer
//the identifying property is the field on the NSManagedObject that will be used to look up our custom identifier
-(id)initWithEntityName:(NSString*)newEntityName andIdentifyingProperty:(NSString*)newIdProp
{
self = [super init];
if (self != nil) {
entityName = [newEntityName retain];
identifyingProperty = [newIdProp retain];
}
return self;
}
-(NSManagedObject*)findObjectForID:(NSString*)identifier
{
if(identifier == nil)
{
return nil;
}
if(!objectList)
{
NSManagedObjectContext *moc = [(AppDelegate*)[UIApplication sharedApplication].delegate managedObjectContext];
NSEntityDescription *entityDescription = [NSEntityDescription
entityForName:entityName inManagedObjectContext:moc];
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
[request setEntity:entityDescription];
NSError *error;
NSArray *array = [moc executeFetchRequest:request error:&error];
objectList = [[NSMutableDictionary dictionary] retain];
for (NSManagedObject* p in array) {
NSString* itemId = [p valueForKey:identifyingProperty];
[objectList setObject:p forKey:itemId];
}
}
NSManagedObject* returnedObject = [objectList objectForKey:identifier];
return returnedObject;
}
-(NSManagedObject*)createObjectForID:(NSString*)identifier
{
NSManagedObject* returnedObject = [NSEntityDescription
insertNewObjectForEntityForName:entityName
inManagedObjectContext:[(AppDelegate*)[UIApplication sharedApplication].delegate managedObjectContext]];
[returnedObject setValue:identifier forKey:identifyingProperty];
[objectList setObject:returnedObject forKey:identifier];
return returnedObject;
}
- (void) dealloc
{
DESTROY(entityName);
DESTROY(identifyingProperty);
[super dealloc];
}
#end
This page provides some help on optimizing performance:
http://developer.apple.com/documentation/Cocoa/Conceptual/CoreData/Articles/cdPerformance.html#//apple_ref/doc/uid/TP40003468-SW1
While not very efficient, why not just build them in-memory with a NSDictionary? Read everything from Core Data into a NSDictionary then merge in your data, replacing everything in Core Data.