Pulling back the curtain on Core Data Chris Mar Spree Commerce http://cmar.me Saturday, February 18, 12

Chris Mar • Spree Commerce • iOS and Rails Developer • @cmar • Grassy Knoll Apps - Redskins Radar Saturday, February 18, 12

Goal Pull back the curtain on Core Data so you will use it on your next project without fear! (we’ll focus on concepts, not a tutorial) Saturday, February 18, 12

Core Data • Object Relational Mapping • Gives you access to a database without using sql or parsing results • Cocoa API with XCode tooling to assist you • Hibernate for Java, ActiveRecord for Rails Saturday, February 18, 12

Storage Types • SQLite Database • XML • In-Memory we’ll focus on SQLite Saturday, February 18, 12

NSManagedObject • Row from the database • Key-Value coding for fields • Optionally subclass • Fetched from NSManagedObjectContext [employee valueForKey:@"name"]; Saturday, February 18, 12

Managed Objects NSManagedObjectContext object1 object2 object1 SQLite Database NSPersistentStoreCoordinator NSManagedObjectModel object2 object1 Saturday, February 18, 12

FetchRequest for NSManagedObjects NSFetchRequest *request = [[NSFetchRequest alloc] init]; [request setEntity:[NSEntityDescription entityForName:@"Order" inManagedObjectContext:self.managedObjectContext]]; [request setPredicate:[NSPredicate predicateWithFormat:@"name like %@", @"*7*"]]; NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES]; NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil]; [request setSortDescriptors:sortDescriptors]; self.orders = [self.managedObjectContext executeFetchRequest:request error:&error]; [sortDescriptor release]; [sortDescriptors release]; [request release]; Saturday, February 18, 12

The Big 3 NSManagedObjectContext NSPersistentStoreCoordinator NSManagedObjectModel .xcdatamodel sqlite Saturday, February 18, 12

NSManagedObjectContext • Object space for Managed Objects • Fetches from Persistent Store • Exclusive to a single thread • Commit and Discard Changes Saturday, February 18, 12

NSManagedObjectContext (lazy loaded in AppDelegate) - (NSManagedObjectContext *)managedObjectContext { if (__managedObjectContext != nil) { return __managedObjectContext; } NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator]; if (coordinator != nil) { __managedObjectContext = [[NSManagedObjectContext alloc] init]; [__managedObjectContext setPersistentStoreCoordinator:coordinator]; } return __managedObjectContext; } Saturday, February 18, 12

NSPersistentStoreCoordinator • Manages connections to stores • Maps data model to database • Handles many stores • Shared between threads Saturday, February 18, 12

NSPersistentStoreCoordinator (lazy loaded in AppDelegate) - (NSPersistentStoreCoordinator *)persistentStoreCoordinator { if (__persistentStoreCoordinator != nil) { return __persistentStoreCoordinator; } NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"MyApp.sqlite"]; NSError *error = nil; __persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]]; if (![__persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) { } return __persistentStoreCoordinator; } Saturday, February 18, 12

NSManagedObjectModel • Definition of database schema • Describes entity objects in store • Predefined Queries - Fetch Requests • Relationships between entities Saturday, February 18, 12

NSManagedObjectModel (lazy loaded in AppDelegate) - (NSManagedObjectModel *)managedObjectModel { if (__managedObjectModel != nil) { return __managedObjectModel; } NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"MyApp" withExtension:@"momd"]; __managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL]; return __managedObjectModel; } Saturday, February 18, 12

NSManagedObjectModel XCode Editor Saturday, February 18, 12

Insert new NSManagedObject NSManagedObject *car = [NSEntityDescription insertNewObjectForEntityForName:@"Car” inManagedObjectContext:self.managedObjectContext]; [car setValue:@"Jeep" forKey:@"name"]; //Save the whole context which will save all the objects in it NSError *error = nil; if ([self.managedObjectContext save:&error]) { NSLog(@"Saved"); } else { NSLog(@"Error saving %@", [error localizedDescription]); } Saturday, February 18, 12

Threads Thread1 Thread2 NSManagedObjectContext NSPersistentStoreCoordinator NSManagedObjectContext Object id=1 Object id=1 Pass ID between threads Object id=1 Object id=1 SQLite Database Object id=1 Saturday, February 18, 12

Memory Usage • Load into an Array • All in memory • Updates • Fast and Easy for small tables self.orders = [self.managedObjectContext executeFetchRequest:request error:&error]; Saturday, February 18, 12

NSFetchedResultsController • Efficiently backs a UITableView • Reduces memory usage • Caches results • Updates table for changes Saturday, February 18, 12

NSFetchedResultsController NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"]; Saturday, February 18, 12

The Big Picture NSManagedObjectContext NSPersistentStoreCoordinator NSManagedObjectModel .xcdatamodel sqlite NSFetchedResultsController iPod touch iPhone iPad Steve Jobs Rocks UITableView NSManagedObject NSManagedObject NSManagedObject NSManagedObject NSManagedObject Saturday, February 18, 12

Relationships • to-one • NSManagedObject *manager = [employee valueForKey:@”manager”]; • to-many • NSSet *directReports = [manager valueForKey:@”directReports”]; • Define inverses for data integrity • Delete Rules - nullify, cascade, deny Saturday, February 18, 12

Fetched Properties • Lazy loaded query relationship • Sorted • Predicate - filtered • “Give a list of direct reports that begin with the letter C” Saturday, February 18, 12

Fetch Requests • Uses NSPredicate for Where clause • Uses NSSortDescriptor for Order By clause • Can be saved with Managed Object Model [fetchRequestTemplateForName] Saturday, February 18, 12

Predicates • [NSPredicate predicateWithFormat:@"name CONTAINS[c] %@", searchText]; • @"name BETWEEN %@", [NSArray arrayWithObjects:@”a”,@”b”,nil] • MATCHES for regex • CONTAINS[c] for case insenstivity • AND, OR, NOT Saturday, February 18, 12

Default Project with Core Data AppDelegate RootViewController NSManagedObjectContext 1. [awakeFromNib] set managedObjectContext 2. [managedObjectContext] lazy load fetchedResultsController 3. [cellForRowAtIndexPath] lazy load fetchedResultsController Saturday, February 18, 12

SQLite Tables Saturday, February 18, 12

Z_PRIMARYKEY Saturday, February 18, 12

Preloaded Database • Load up database using Base • Base lets you import csv • Make sure you set the primary keys • On start check for existence, then copy it over Saturday, February 18, 12

Preloading Database NSString *storePath = [[self applicationDocumentsDirectory] stringByAppendingPathComponent: @"products.sqlite"]; NSURL *storeUrl = [NSURL fileURLWithPath:storePath]; // Put down default db if it doesn't already exist NSFileManager *fileManager = [NSFileManager defaultManager]; if (![fileManager fileExistsAtPath:storePath]) { NSString *defaultStorePath = [[NSBundle mainBundle] pathForResource:@"preloaded_products" ofType:@"sqlite"]; if (defaultStorePath) { [fileManager copyItemAtPath:defaultStorePath toPath:storePath error:NULL]; } } Saturday, February 18, 12

FMDB • Objective-C wrapper for SQLite • Direct access • Low overhead • Great for simple data needs • https://github.com/ccgus/fmdb Saturday, February 18, 12

FMDB Example FMDatabase *db = [FMDatabase databaseWithPath:@"/tmp/my.db"]; [db open] FMResultSet *rs = [db executeQuery:@"select * from orders where customer_id = ?", @"1000"]; [rs intForColumn:@"c"], [rs stringForColumn:@"b"], [rs dateForColumn:@"d"], [rs doubleForColumn:@"e"]); } [rs close]; [db close]; Saturday, February 18, 12

Links • http://www.raywenderlich.com/934/core-data- tutorial-getting-started • http://menial.co.uk/software/base/ • https://github.com/ccgus/fmdb Saturday, February 18, 12

Thank You! @cmar on twitter http://cmar.me Saturday, February 18, 12