Managed Object Model schema Persistent Store Coordinator connection Managed Object Context scratch pad

Transcription

1 CoreData Tutorial

2 What is CoreData?

3 CoreData Stack Managed Object Model: You can think of this as the database schema. It is a class that contains definitions for each of the objects (also called Entities ) that you are storing in the database. Usually, you will use the visual editor to set up what objects are in the database, what their attributes are, and how they relate to each other. However, you can do this with code, too. Persistent Store Coordinator: You can think of this as the database connection. Here s where you set up the actual names and locations of what databases will be used to store the objects, and any time a managed object context needs to save something it goes through this single coordinator. Managed Object Context: You can think of this as a scratch pad for objects that come from the database. It s also the most important of the three for us, because we ll be working with this the most. Basically, whenever you need to get objects, insert objects, or delete objects, you call methods on the managed object context.

4 A Simple Example (Using Entities) Step #1 Create your schema Step #2 Inserting an object Step #3 Querying for an object

5 Create Your Schema

6 Create Your Schema

7 Create Your Schema

8 Create Your Schema

9 Insert an Object // Get the ManagedObjectContext NSManagedObjectContext *context = self.managedobjectcontext; // Create a new ManagedObject for the course NSManagedObject *newcourse = [NSEntityDescription insertnewobjectforentityforname:@ Course" inmanagedobjectcontext:context]; // Create a new ManagedObject for the assignment NSManagedObject *newtask = [NSEntityDescription insertnewobjectforentityforname:@ Assignment" inmanagedobjectcontext:context];

10 // Create a new ManagedObject for the assignment Insert an Object (cont) NSManagedObject *newtask = [NSEntityDescription insertnewobjectforentityforname:@ Assignment" inmanagedobjectcontext:context]; // Set the properties of our new course NSMutableSet *tasks = [NSMutableSet setwithobject:newtask]; [newcourse setvalue:@ CprE 388X" forkey:@"name"]; [newcourse setvalue:tasks forkey:@ tasks"]; // Set the properties of our new assignment [newtask setvalue:@ HW6" forkey:@ name"]; [newtask setvalue:@ CoreData assignment" forkey:@ details"]; [newtask setvalue:newcourse forkey:@ course"]; // Save the context if (![context save:nil]) { // error checking }

11 Insert an Object (Review) Methods Used: [NSEntityDescription Course inmanagedobjectcontext:context]; [newcourse CprE 388X"

12 Query for Objects // Create a NSFetchRequest NSFetchRequest *query = [[[NSFetchRequest alloc] init] autorelease]; // Create the entity that should be returned NSEntityDescription *entity = [NSEntityDescription entityforname:@ Course" inmanagedobjectcontext:context]; // Optionally define an NSPredicate and/or NSSortDescriptor to narrow your query // Update your fetch by using setentity, setpredicate (optional), and setsortdescriptor (optional) [query setentity:entity]; // Fetch an NSArray of all Course objects NSArray *results = [context executefetchrequest:query error:nil];

13 Query for Objects (Predicate) // Create a NSFetchRequest NSFetchRequest *query = [[[NSFetchRequest alloc] init] autorelease]; // Create the entity that should be returned NSEntityDescription *entity = [NSEntityDescription entityforname:@ Course" inmanagedobjectcontext:context]; NSPredicate *predicate = [NSPredicate predicatewithformat:@ name = CprE 388 ]; // Update your fetch by using setentity, setpredicate (optional), and setsortdescriptor (optional) [query setentity:entity]; [query setpredicate:predicate]; // Fetch an NSArray of all Course objects NSArray *results = [context executefetchrequest:query error:nil];

14 Query for Objects (cont) How do I play with the results array? for (NSManagedObject *mycourse in results) { } NSString *name = [mycourse valueforkey:@"name"]);

15 A Better Example (Using Classes) Step #1 Create your schema Step #2 Generate your Classes Step #3 Inserting an object Step #4 Querying for an object

16 Update your schema

17 Generate your Classes

18 Generate your Classes

19 Generate your Classes

20 Insert an Object What s different? // Get the ManagedObjectContext NSManagedObjectContext *context = self.managedobjectcontext; // Create a new ManagedObject for the course Course *newcourse = [NSEntityDescription insertnewobjectforentityforname:@ Course" inmanagedobjectcontext:context]; // Create a new ManagedObject for the assignment Assignment *newtask = [NSEntityDescription insertnewobjectforentityforname:@ Assignment" inmanagedobjectcontext:context];

21 #import Course.h #import Assignment.h Insert an Object There s Classes! // Get the ManagedObjectContext NSManagedObjectContext *context = self.managedobjectcontext; // Create a new ManagedObject for the course Course *newcourse = [NSEntityDescription insertnewobjectforentityforname:@ Course" inmanagedobjectcontext:context]; // Create a new ManagedObject for the assignment Assignment *newtask = [NSEntityDescription insertnewobjectforentityforname:@ Assignment" inmanagedobjectcontext:context];

22 // Create a new ManagedObject for the assignment Insert an Object (cont) Assignment *newtask = [NSEntityDescription insertnewobjectforentityforname:@ Assignment" inmanagedobjectcontext:context]; // Set the properties of our new course [newcourse addtasksobject:newtask]; newcourse.name CprE 388X ; // this method was generated for us // Set the properties of our new assignment newtask.course = newcourse; newtask.name HW6 ; newtask.details CoreData assignment ; // Save the context if (![context save:nil]) { // error checking }

23 Query for Objects What s different? // Create a NSFetchRequest NSFetchRequest *query = [[[NSFetchRequest alloc] init] autorelease]; // Create the entity that should be returned NSEntityDescription *entity = [NSEntityDescription entityforname:@ Course" inmanagedobjectcontext:context]; // Optionally define an NSPredicate and/or NSSortDescriptor to narrow your query // Update your fetch by using setentity, setpredicate (optional), and setsortdescriptor (optional) [query setentity:entity]; // Fetch an NSArray of all Course objects NSArray *results = [context executefetchrequest:query error:nil];

24 Query for Objects Nothing! // Create a NSFetchRequest NSFetchRequest *query = [[[NSFetchRequest alloc] init] autorelease]; // Create the entity that should be returned NSEntityDescription *entity = [NSEntityDescription entityforname:@ Course" inmanagedobjectcontext:context]; // Optionally define an NSPredicate and/or NSSortDescriptor to narrow your query // Update your fetch by using setentity, setpredicate (optional), and setsortdescriptor (optional) [query setentity:entity]; // Fetch an NSArray of all Course objects NSArray *results = [context executefetchrequest:query error:nil];

25 Query for Objects (cont) How do I play with the results array? for (Course *mycourse in results) { } NSString *name = mycourse.name;