Core data intermediate Workshop at NSSpain 2013

Diego Freniche / @dfreniche / http://www.freniche.com
Core Data Workshop

Diego Freniche: programmer & teacher

Diego Freniche: programmer & teacher
• @dfreniche
• Freelance Mobile developer: iOS/Android/BB10/
webOS/...
• In a former life Java Certiﬁcations Collector: SCJP
1.5, SCJP 1.6, SCWCD 1.5, SCBCD 1.3
• Some languages: BASIC, PASCAL, C, C++, Delphi,
COBOL, Clipper, Visual Basic, Java, JavaScript,
Objective-C
Hello, World!

Before we start...
• Switch OFF phones

Before we start...
• Been here is funny

Before we start...
• ¡Live the moment!¡Carpe diem!

Before we start...
• ¡Live the moment!¡Carpe diem!
• Ask me a lot. Don’t yawn

What you need (checklist)
• a Mac with OS X capable of running Xcode 4.6.1
• last Xcode 4 installed 4.6.1
• You can also use prerelease software, if you are a registered Apple developer.
No support then, sorry :-D
• SimPholders installed: http://simpholders.com
• SQLLite database browser: http://sqlitebrowser.sourceforge.net
• (optional) set $HOME/Library folder visible, using (from a Terminal)

Diego Freniche / http://www.freniche.com
Idea: Creating the Core Data Stack

The Core Data Stack
Managed Object Context
Persistent Store Coordinator
Persistent Object Store
Managed Object Model

Doubts

Doubts
• Use Apple’s code?

Doubts
• Really?

Doubts
• Really?
• Use a singleton?

Doubts
• Really?
• Don’t use a singleton?

Doubts
• Really?
• Don’t use a singleton?
• Use dependency injection?

Apple’s code

Apple’s code
- (void)saveContext
{
NSError *error = nil;
NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
if (managedObjectContext != nil) {
if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
// Replace this implementation with code to handle the error appropriately.
// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
}
}
#pragma mark - Core Data stack
// Returns the managed object context for the application.
// If the context doesn't already exist, it is created and bound to the persistent store coordinator for the application.
- (NSManagedObjectContext *)managedObjectContext
{
if (_managedObjectContext != nil) {
return _managedObjectContext;
}
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (coordinator != nil) {
_managedObjectContext = [[NSManagedObjectContext alloc] init];
[_managedObjectContext setPersistentStoreCoordinator:coordinator];
}
return _managedObjectContext;
}
// Returns the managed object model for the application.
// If the model doesn't already exist, it is created from the application's model.
- (NSManagedObjectModel *)managedObjectModel
{
if (_managedObjectModel != nil) {
return _managedObjectModel;
}
NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Test" withExtension:@"momd"];
_managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
return _managedObjectModel;
}
// Returns the persistent store coordinator for the application.
// If the coordinator doesn't already exist, it is created and the application's store added to it.
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
if (_persistentStoreCoordinator != nil) {
return _persistentStoreCoordinator;
}
NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"Test.sqlite"];
NSError *error = nil;
_persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
/*
Replace this implementation with code to handle the error appropriately.
abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
Typical reasons for an error here include:
* The persistent store is not accessible;
* The schema for the persistent store is incompatible with current managed object model.
Check the error message to determine what the actual problem was.
If the persistent store is not accessible, there is typically something wrong with the file path. Often, a file URL is pointing into the application's resources directory instead of a writeable directory.
If you encounter schema incompatibility errors during development, you can reduce their frequency by:
* Simply deleting the existing store:
[[NSFileManager defaultManager] removeItemAtURL:storeURL error:nil]
* Performing automatic lightweight migration by passing the following dictionary as the options parameter:
@{NSMigratePersistentStoresAutomaticallyOption:@YES, NSInferMappingModelAutomaticallyOption:@YES}
Lightweight migration will only work for a limited set of schema changes; consult "Core Data Model Versioning and Data Migration Programming Guide" for details.
*/
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
return _persistentStoreCoordinator;
}
#pragma mark - Application's Documents directory
// Returns the URL to the application's Documents directory.
- (NSURL *)applicationDocumentsDirectory
{
return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}

Apple’s code problems
• Core Data Stack inside AppDelegate?
• Really?
• Separation of concerns?
• Only one Managed Object Context

Create our own Core Data Stack

• In one “simple” method

• Singleton / not singleton?

• Singleton / not singleton?
• Use both!

Dependency injection? Or singletons FTW?
• It depends :-)

Idea: using asserts to check threads

Asserts
• Check if we are running UI code in the UI Thread
• Check if we are NOT running Core Data code in the UI Thread

Asserts
• Check if we are running UI code in the UI Thread
• Check if we are NOT running Core Data code in the UI Thread
#define DF_ASSERT_MAIN_THREAD [NSThread isMainThread]?:(NSLog(@"NOT IN MAIN
THREAD"),abort())

Idea: create a common UITableView/Core data
class

Idea: use an NSManagedObject subclass

Entities Design Tips

• Always add ﬁeld order

• Try to create a good UML diagram at ﬁrst

• Try to create a good UML diagram at ﬁrst
• Have an NSString constant with every Entity’s name inside .h

Extend NSManagedObject
• Editor > Create NSManagedObject subclass...
• creates @dynamic properties
• getter / setter generated in runtime (@property in compile time)
• Core Data doesn’t know at compile time if the persistent store is going to
be XML or a DB (or in-memory)

• overwrite init to call designated initializer

• overwrite init to call designated initializer
-(id)init {
NSManagedObjectContext *context = [[CoreDataStack coreDataStack]
managedObjectContext];
return [self initWithEntity:[NSEntityDescription
entityForName:kRETROITEM_ENTITY inManagedObjectContext:context ]
insertIntoManagedObjectContext:context];
}

Validate Properties
• One for every property, if we want it
• Passing parameter by reference
• It should return YES if validation is passed

Validate Properties
• One for every property, if we want it
• Passing parameter by reference
• It should return YES if validation is passed
-(BOOL)validateName:(id *)ioValue error:(NSError * __autoreleasing *)outError;

Validator for operations
• First thing: must call [super ...]
• Useful to check business rules (using several properties)

Validator for operations
• First thing: must call [super ...]
• Useful to check business rules (using several properties)
- (BOOL)validateForDelete:(NSError **)error
- (BOOL)validateForInsert:(NSError **)error
- (BOOL)validateForUpdate:(NSError **)error

Support for KVO
• Good for Faults

Support for KVO
• Good for Faults
- (void)willAccessValueForKey:(NSString *)key

Idea: use Mogenerator

Mogenerator
created by Jonathan 'Wolf' Rentzsch

Mogenerator (quoting from the web page)

• http://rentzsch.github.io/mogenerator/

• generates Objective-C code for your Core Data custom classes

• Unlike Xcode, mogenerator manages two classes per entity: one for
machines, one for humans

• Unlike Xcode, mogenerator manages two classes per entity: one for
machines, one for humans
• The machine class can always be overwritten to match the data model,
with humans’ work eﬀortlessly preserved

Installing mogenerator

Using it
• it’s a script, so we can launch it from command line
• using iTerm, DTerm, etc.
• Best way: to have it inside our project
• Create a new Aggregate Target (New Target > Other > Aggregate)
• Add Build Phase > Add Run Script

Using it
• it’s a script, so we can launch it from command line
• using iTerm, DTerm, etc.
• Best way: to have it inside our project
• Create a new Aggregate Target (New Target > Other > Aggregate)
• Add Build Phase > Add Run Script
mogenerator --template-var arc=true -m RetroStuffTracker/
RetroStuffTracker.xcdatamodeld/RetroStuffTracker.xcdatamodel/

Two classes
• _MyClass.*: machine generated
• *MyClass.*: human edited
• Never, ever recreate the classes
again from the Core Data Model

Two classes

#import "_RetroItem.h"
@interface RetroItem : _RetroItem {}
// Custom logic goes here.
@end
Two classes

#import "_RetroItem.h"
@interface RetroItem : _RetroItem {}
@end
#import "RetroItem.h"
@interface RetroItem ()
// Private interface goes here.
@end
@implementation RetroItem
@end
Two classes

Idea: use Magical Record

Magical record != avoid Core Data at all costs

• Just a bunch of categories to help you write less code

• You have to know your sh*t

• CocoaPods friendly

• Ideal: use Unit testing + Mogenerator + CocoaPods + Magical Record

• My point: 7 people, 7 ideas, all great

• My point: 7 people, 7 ideas, all great
• all diﬀerent

Core data intermediate Workshop at NSSpain 2013

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