iPhone core data inserting new objects

Question

I have been reading through the core data documentation and feel I am still missing something.

I do not quite understand how you insert objects into a relationship of another object.

For example the following two Entities are in my model

flightDepartureBoard
 name: 
 from_airport:
 to_airport:
 current_flights: (this is a one to many relationship of flight detail entities)

flight_details
 arrive
 depart
 name

So my data contains a list of different departure boards for a few airports. Each departure board then contains a number of flight_details containing info on the current arrivals and departures for that airport.

My current understanding is to insert the flight details for a specific departure board, I must get the managedObject for the board, then create a new managed object for each flight and set its values as appropriate then create an NSSet conatining the flight managed objects and set the depatureboards managedObject current_flights (the relationship) to the just created NSSet. Is this correct?

What if I want to add new entries? I assume I do not need to fetch the entire set first?

Thanks for any help..

---

Although I just realised I could set the relationship to the current object on the flightDetails object instead..

Answer 1

There are a few options:
1. You can use add<Key>Object: on a NSManagedObject:

NSManagedObject *flightBoard = [NSEntityDescription insertNewObjectForEntityForName:@"FlightDepartureBoard" inManagedObjectContext:self.managedObjectContext];
NSManagedObject *details = [NSEntityDescription insertNewObjectForEntityForName:@"Flight_Details" inManagedObjectContext:self.managedObjectContext];
[flightBoard addCurrent_flightsObject:details];

Although you will get a compiler warning unless you define the accessors in a category:

@interface NSManagedObject (Current_flightsAccessors)
- (void)addCurrent_flightsObject:(NSManagedObject *)value;
- (void)removeCurrent_flightsObject:(NSManagedObject *)value;
- (void)addCurrent_flights:(NSSet *)value;
- (void)removeCurrent_flights:(NSSet *)value;
@end

2. Subclass. You can generate class files from your model which will include accessors for the to-many relationships:

FlightDepartureBoard.h:

#import <CoreData/CoreData.h>
@class Flight_Details;
@interface FlightDepartureBoard : NSManagedObject 
{
}
@property (nonatomic, retain) NSString * name;
@property (nonatomic, retain) NSString * from_airport;
@property (nonatomic, retain) NSString * to_airport;

@interface FlightDepartureBoard (CoreDataGeneratedAccessors)
- (void)addCurrent_flightsObject:(Flight_Details *)value;
- (void)removeCurrent_flightsObject:(Flight_Details *)value;
- (void)addCurrent_flights:(NSSet *)value;
- (void)removeCurrent_flights:(NSSet *)value;
@end

FlightDepartureBoard.m:

#import "FlightDepartureBoard.h"
#import "Flight_Details.h"
@implementation FlightDepartureBoard
@dynamic name;
@dynamic from_airport;
@dynamic to_airport;
@dynamic current_flights;
@end

3. You can get the mutable set and modify it using mutableSetValueForKey:. For example:

NSManagedObject *flightBoard = [NSEntityDescription insertNewObjectForEntityForName:@"FlightDepartureBoard" inManagedObjectContext:self.managedObjectContext];
NSManagedObject *details = [NSEntityDescription insertNewObjectForEntityForName:@"Flight_Details" inManagedObjectContext:self.managedObjectContext];
NSMutableSet *flights = [flightBoard mutableSetValueForKey:@"current_flights"];
[flights addObject:details];

For more information, check out Managed Object Accessor Methods.