Core data basic Workshop slides 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
Core Data: developer’s ﬁrst impression

Core Data in 547 easy steps slide 6/320

Core Data terms
• Entity
• an entity in our model == Object in memory == row in table
• Attribute
• Relationship
• Object graph
http://ogre.berniecode.com/ogre_white_paper

To get the most out of Core Data
• KVC, KVO
• ARC, memory management
• delegate & MVC patterns
• singletons are evil (more or less)

Core Data Hello World!

The Problem
• Objet - Relational impedance
• SQL: 70s/80s
• OOP: 80s-

Exhibit 1: composition
Person
+name: String
+idCard: idCard
+bankAccout: bankAccount

Person
+name: String
+idCard: idCard
idCard
+number: int
+letter: char
+checkLetter()

id name idCard
Person
+name: String
+idCard: idCard
idCard
+number: int
+letter: char
+checkLetter()

id name idCard
Person
+name: String
+idCard: idCard
idCard
+number: int
+letter: char
+checkLetter()
VARCHAR

id name idCard
Person
+name: String
+idCard: idCard
idCard
+number: int
+letter: char
+checkLetter()
VARCHAR ¿?

Employee
+empNumber: int
Person
+name: String
+idCard: idCard
Exhibit 2: inheritance

Employee
+empNumber: int
Person
+name: String
+idCard: idCard
Politician
+moneyTaken: double

Employee
+empNumber: int
Person
+name: String
+idCard: idCard
Hyena
Politician
+moneyTaken: double

Exhibit 3: collection modelling
Person
+name: String
+bills: Bill[]
Bill
0..*1
http://en.wikipedia.org/wiki/First_normal_form

Relational World
• tables
• cartesian products
• rows/ columns
• normal forms
• Objects
• object collections
• composition
• inheritance
OO World

The solution: ORM
• Object Relational Mapper
• Hibernate (Java, .Net)
• Core Data (Cocoa)
• Core Data is our model
• can persist our objects
in several ways

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

Our Model
NSManagedObjectContext
NSManagedObject
NSManagedObject
NSManagedObject
NSManagedObject
NSObject
PersistedIn memory only

Managed Object Context: MOC
• Managed Object Context: in-memory space where CD manages all our
model’s objects.
• All CRUD is done against a MOC. We persist data using save:
• Our model’s objects are Managed Objects.
• The MOC needs a Persistent Store Coordinator to save the object graph in
persistent store.

• Maps our model objects into database tables.
• Objects == NSManagedObject
• Classes == NSEntityDescription
• We describe our App entities inside a MOM
• stored inside .xcdatamodeld ﬁles in Xcode. Compiles into .momd
• graphic editor / class generator (dumb)

Persistent Store Coordinador
Makes the mapping between our App’s objects and the physical storage inside
the Persistent Object Store.
99% time we’ll work with ONE Object Store, but it’s possible use more than one.
For example, a sqlite DB with recipes and another DB with notes, stars, etc.
Coordinator: single façade to work with diﬀerent Stores.
A managed object context can then create an object graph based on the union of
all the data stores the coordinator covers
Coordinator: serializes operations

NSXMLStoreType (XML only OS X, bad performance)
NSSQLiteStoreType (partial object graph in memory)
NSBinaryStoreType (kind of NIBs, poor performance)
NSInMemoryStoreType (good for testing)
Makes the mapping between our App’s objects and the physical storage inside
the Persistent Object Store.
Supported Store Types

SQL in SQLite
• http://sqlite.org/lang.html
• We can see generated SQL: -com.apple.CoreData.SQLDebug 1
• Schemes > Edit Scheme > Test > Arguments

1
2
3

Accessing SQLite
sqlitebrowser.sourceforge.net
Look in:
/Users/<usuario>/Library/Application
Support/iPhone Simulator/<versión>/
Applications/<ID App>/Documents/
<archivo SQLite>

DDL: Data Deﬁnition Language
• CREATE DATABASE, CREATE TABLE, CREATE INDEX, ALTER TABLE, DROP
INDEX, ...
• All written by Core Data
• We DO NOT have to create anything: neither tables nor database
• If we make changes, Core Data alters tables, columns, indexes...

Modelling
We need a Data Model ﬁle to “draw” our model
1st, create all our model’s entities, then add
attributes
Can subclass NSManagedObject to use compiler-
time name checking, Xcode’s autoﬁll,...

Modelling
• New model versions: Editor > Add
Model Version
• Model (.xcdatamodeld) is a folder
• Last version has no number. Oldest
with higher number. WTF, Apple!
(WTF: What a Tricky Fact)
• 1st time we access model it
creates persintent store lazily
Select THIS

Versioning and changes
• Activate always lightweight migration
• If we make changes to the model, not changing version, version used in the
model and version used to create DB doesn’t match: delete DB.
• Reseting Content and Settings.. in Simulator
• delete (by hand) .sqlite ﬁle

NSManagedObject
NSManagedObject
NSManagedObjectContext
NSEntityDescription

NSManagedObject
• base class implementing all “basic” object model behavior
• We can NOT use Core Data with NSObject, we HAVE TO use
NSManagedObject
• Our model classes inherit from NSManagedObject
• not mandatory, but...
• allows us to add logic, use @property, get notiﬁcations...
• have to be properly conﬁgured

Entities Design
• Always add ﬁeld order
• 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

Inserting Entities (INSERT INTO)
insertNewObjectForEntityForName context save
Context

Inserting Entities (INSERT INTO)
// using NSEntityDescription. Pass: entity name and context
[NSEntityDescription insertNewObjectForEntityForName:@”MyEntity” inManagedObjectContext:context];
[retroItem setValue:@"Spectrum 48K" forKey:@"name"];
[retroItem setValue:@100.00 forKey:@"acquisitionCost"];
[retroItem setValue:[NSDate new] forKey:@"dateAcquired"];
insertNewObjectForEntityForName context save
Context

Fetching entities (SELECT)
• Query with NSFetchRequest
• SELECT by deﬁnition is unordered
• At least we need to provide
• entity
• order by

Step by Step fetch (Select)
1
2
3
4
5
6

Step by Step fetch (Select)
NSManagedObjectContext *context = [[CoreDataStack coreDataStack] managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:kRETRO_ITEM_ENTITY
inManagedObjectContext:context];
[fetchRequest setEntity:entity];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:NO];
[fetchRequest setSortDescriptors:@[sortDescriptor]];
NSError *error = nil;
NSArray *distincResults = [context executeFetchRequest:fetchRequest error:&error];
1
2
3
4
5
6

Order querys
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"fecha_max" ascending:YES];
NSManagedObject returned inside NSArray are unordered unless otherwise we
provide NSSortDescription.
1st, we create the sort descriptor
[request setSortDescriptors:[NSArray arrayWithObject:sortDescriptor]];
Then we add to our NSFetchRequest the sort descriptors array:

Filtering querys
NSManagedObjectContext *moc = [self managedObjectContext];
NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Employee"
inManagedObjectContext:moc];
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
[request setEntity:entityDescription];
NSNumber *minimumSalary = ...;
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(lastName LIKE[c] 'Worsley') AND (salary
> %@)", minimumSalary];
[request setPredicate:predicate];
NSArray *array = [moc executeFetchRequest:request error:&error];
NSFetchRequest returns an array of NSManagedObject. We can use a
NSPredicate to ﬁlter.
Filter/NSPredicate acts here as the SQL WHERE clause.
We need to add that query with setPredicate.

Delete Entities (DELETE)
+ (void)deleteInstancesForEntityName:(NSString *)entityName inContext:(NSManagedObjectContext *)context {
NSFetchRequest *fetch = [[NSFetchRequest alloc] init];
[fetch setEntity:[NSEntityDescription entityForName:entityName inManagedObjectContext:context]];
NSArray *dataObjects = [context executeFetchRequest:fetch error:&error];
for (NSManagedObject *dataObject in dataObjects) {
[context deleteObject:dataObject];
}
NSError *saveError = nil;
[context save:&saveError];
}

Object identiﬁcator

Object identiﬁcator
NSManagedObjectID *moID = [managedObject objectID];
-(NSManagedObject *)existingObjectWithID:(NSManagedObjectID *)objectID
error:(NSError **)error

Accessing Properties
Sometimes we don’t want the whole object (NSManagedObject) only the value of a property applying a function
(max, min, etc.).
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Event" inManagedObjectContext:context];
[request setEntity:entity];
1. Create NSFetchRequest as usual
[request setResultType:NSDictionaryResultType];
2. Tell NSFetchRequest to return NSDictionary instead NSArray:
NSExpression *keyPathExpression = [NSExpression expressionForKeyPath:@"creationDate"];
NSExpression *minExpression = [NSExpression expressionForFunction:@"min:" arguments:[NSArray
arrayWithObject:keyPathExpression]];
3. Deﬁne the ﬁeld to calc upon (NSExpression), then the function

Accessing Properties
NSExpressionDescription *expressionDescription = [[NSExpressionDescription alloc] init];
[expressionDescription setName:@"minDate"];
[expressionDescription setExpression:minExpression];
[expressionDescription setExpressionResultType:NSDateAttributeType];
4. Create a NSExpressionDescription:
[request setPropertiesToFetch:[NSArray arrayWithObject:expressionDescription]];
NSArray *objects = [managedObjectContext executeFetchRequest:request error:&error];
5. Set in the query the properties to fetch
if ([objects count] > 0) {
NSLog(@"Minimum date: %@", [[objects objectAtIndex:0] valueForKey:@"minDate"]);
}
6. Access our result:

Relationship example
NSManagedObjectContext *context = [self managedObjectContext];
NSManagedObject *failedBankInfo = [NSEntityDescription
insertNewObjectForEntityForName:@"FailedBankInfo"
[failedBankInfo setValue:@"Test Bank" forKey:@"name"];
[failedBankInfo setValue:@"Testville" forKey:@"city"];
[failedBankInfo setValue:@"Testland" forKey:@"state"];
NSManagedObject *failedBankDetails = [NSEntityDescription
insertNewObjectForEntityForName:@"FailedBankDetails"
[failedBankDetails setValue:[NSDate date] forKey:@"closeDate"];
[failedBankDetails setValue:[NSDate date] forKey:@"updateDate"];
[failedBankDetails setValue:[NSNumber numberWithInt:12345] forKey:@"zip"];
[failedBankDetails setValue:failedBankInfo forKey:@"info"];
[failedBankInfo setValue:failedBankDetails forKey:@"details"];
NSError *error;
if (![context save:&error]) {
NSLog(@"Whoops, couldn't save: %@", [error localizedDescription]);
}
Escritura

Relationship example
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription
entityForName:@"FailedBankInfo" inManagedObjectContext:context];
[fetchRequest setEntity:entity];
NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
for (NSManagedObject *info in fetchedObjects) {
NSLog(@"Name: %@", [info valueForKey:@"name"]);
NSManagedObject *details = [info valueForKey:@"details"];
NSLog(@"Zip: %@", [details valueForKey:@"zip"]);
}
Read

NSFetchedResultsController
• Controller without interface
• Purpose: “feed” with data an UITableView
• Protocol NSFetchedResultsControllerDelegate
• section “Typical Use”: there’s the code found in template
• connected to a Context: if there are changes of any object inside that
context it receives a notiﬁcation and updates automatically

SQLite
UITableView

SQLite
UITableView
???

Context
NSManagedObject
NSManagedObject
NSManagedObject
SQLite
UITableView
???

Context
NSManagedObject
NSManagedObject
NSManagedObject
SQLite
UITableView NSFetchedResultsController
???
delegate

Context
NSManagedObject
NSManagedObject
NSManagedObject
SQLite
UITableView NSFetchedResultsController
delegate

Attributions
• http://www.flickr.com/photos/paldies/85684217/
• http://www.flickr.com/photos/56380734@N05/6808753611/
• http://www.flickr.com/photos/msimdottv/4339697089/
• http://www.flickr.com/photos/mobilestreetlife/4179063482/
• http://www.flickr.com/photos/owldreams/4428782193/
• http://www.flickr.com/photos/miss_pupik/73160522/
• http://kfannerd713.deviantart.com/art/UNICORN-PUKING-RAINBOWS-WHAAAA-152117816
• http://www.flickr.com/photos/wwworks/4759535950/
• http://www.flickr.com/photos/barto/28135419/sizes/l/in/photolist-3ucFr-7aiwZ-aqWUu-bLebi-cDeVC-jt2YW-jWW1t-kQ25f-m86XP-swafK-yHMbE-yHMcc-yHMda-

Core data basic Workshop slides NSSpain 2013

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