Adding unique objects to Core Data


Adding unique objects to Core Data



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]; } 

Persisting Custom Objects

1:

Checkbox in iOS application
This page provides any guidance on optimizing performance: http://developer.apple.com/documentation/Cocoa/Conceptual/CoreData/Articles/cdPerformance.html#//apple_ref/doc/uid/TP40003468-SW1. What is the AppDelegate for and how do I know when to use it? 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.. Concatenating NSArray contents with NSMutableString AppendString
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2:

need a 24 bits type in objc
Check out the section titled "Batch Faulting" on the page titled "Core Data Performance" in Xcode's Core Data Programming Guide this Norman linked to in his answer.. Photo Library view stays on screen after choosing an image with UIImagePickerController 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 quick fix 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 this did exist only if their updated attrialthough e is older than this of the one from the server..

3:

I've gotten all this to job 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 any ID, and must create it for any 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 another things there, pure find/create is likely faster).. It does this by caching a dictionary of all the NSManagedObjects, and checking this cache rather than executing a new NSFetchRequest. . A couple of modifications this could guidance things speed up even further: 1. Get only selected properties for the NSManagedObjects 2. Only receive 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 (although 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 this 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 


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