iOSDevCamp 2011 Core Data

Pulling back the curtain on
Core Data
Chris Mar
Spree Commerce
http://cmar.me

Chris Mar

• Spree Commerce

• iOS and Rails Developer

• @cmar

• Grassy Knoll Apps - Redskins
Radar

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)

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

Storage Types
• SQLite Database

• XML

• In-Memory

we’ll focus on SQLite

NSManagedObject
• Row from the database

• Key-Value coding for fields

• Optionally subclass

• Fetched from NSManagedObjectContext

[employee valueForKey:@"name"];

Managed Objects
object1 object2

object1 object2

NSManagedObjectContext

NSPersistentStoreCoordinator

NSManagedObjectModel

object1

SQLite Database

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];

The Big 3

NSPersistentStoreCoordinator sqlite

NSManagedObjectModel .xcdatamodel


• Object space for Managed Objects

• Fetches from Persistent Store

• Exclusive to a single thread

• Commit and Discard Changes

(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;
}


• Manages connections to stores

• Maps data model to database

• Handles many stores

• Shared between threads


- (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;
}


• Definition of database schema

• Describes entity objects in store

• Predefined Queries - Fetch Requests

• Relationships between entities


- (NSManagedObjectModel *)managedObjectModel
{
if (__managedObjectModel != nil)
{
return __managedObjectModel;
}

NSURL *modelURL = [[NSBundle mainBundle]
URLForResource:@"MyApp" withExtension:@"momd"];

__managedObjectModel = [[NSManagedObjectModel alloc]
initWithContentsOfURL:modelURL];

return __managedObjectModel;
}

XCode Editor

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]);
}

Threads
Pass ID between threads

Thread1 Thread2

Object id=1 Object id=1

Object Object
NSManagedObjectContext NSManagedObjectContext
id=1 id=1


SQLite Database

Object id=1

Memory Usage
self.orders = [self.managedObjectContext executeFetchRequest:request error:&error];

• Load into an Array

• All in memory

• Updates

• Fast and Easy for small tables

NSFetchedResultsController

• Efficiently backs a UITableView

• Reduces memory usage

• Caches results

• Updates table for changes


NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController
alloc]
initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext
sectionNameKeyPath:nil cacheName:@"Root"];

The Big Picture
UITableView
NSManagedObject
NSManagedObject iPhone
NSManagedObject iPod touch
NSManagedObject
iPad
NSManagedObject
NSManagedObjectContext Steve Jobs Rocks

NSPersistentStoreCoordinator sqlite

NSManagedObjectModel .xcdatamodel

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

Fetched Properties

• Lazy loaded query relationship

• Sorted

• Predicate - filtered

• “Give a list of direct reports that begin with the
letter C”

Fetch Requests

• Uses NSPredicate for Where clause
• Uses NSSortDescriptor for Order By clause
• Can be saved with Managed Object Model
[fetchRequestTemplateForName]

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

Default Project with Core

1. [awakeFromNib]
AppDelegate RootViewController
set managedObjectContext

2. [managedObjectContext] 3. [cellForRowAtIndexPath]
lazy load lazy load fetchedResultsController

NSManagedObjectContext fetchedResultsController

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

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];
}
}

FMDB
• Objective-C wrapper for SQLite

• Direct access

• Low overhead

• Great for simple data needs

• https://github.com/ccgus/fmdb

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];

Links
• http://www.raywenderlich.com/934/core-data-
tutorial-getting-started

• http://menial.co.uk/software/base/
• https://github.com/ccgus/fmdb

Thank You!

@cmar on twitter
http://cmar.me

iOSDevCamp 2011 Core Data

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Editor's Notes