One to many relationship: not able to save - ios

Question

I am trying to create a one to many relationship with some data I have.
I have a single Project and many items, I am trying to set up the controller to save them but this is the first time I have ever used a one to many relationship and my head is about to explode.
This is what my save method looks like
- (void)writeProj:(NSArray *)recivedProData ItemsData:(NSArray *)itemsData {
// WRITE TO CORE DATA
NSManagedObjectContext *context = [self managedObjectContext];
for (NSDictionary *dict in recivedProData) {
Project *project = [NSEntityDescription insertNewObjectForEntityForName:#"Project" inManagedObjectContext:self.managedObjectContext];
project.projectNumber = [dict valueForKey:#"ProjectNumber"];
project.projectDescription = [dict valueForKey:#"Description"];
// project.items = [dict valueForKey:#""]; // this is the relationship for project
}
for (NSDictionary *dict in itemsData) {
Items *items = [NSEntityDescription insertNewObjectForEntityForName:#"Items" inManagedObjectContext:self.managedObjectContext];
items.description = [dict valueForKey:#"Description"];
items.area = [dict valueForKey:#"Area"];
items.stage = [dict valueForKey:#"Stage"];
// items.project = [dict valueForKey:#""]; // this is the relationship for items
}
NSError *error = nil;
if (![__managedObjectContext save:&error]) {
NSLog(#"There was an error! %#", error);
}
else {
NSLog(#"created");
}
[Project addItemsObject:items];
[__managedObjectContext saveOnSuccess:^{
NSLog(#"You created a relationship");
} onFailure:^(NSError *error) {
NSLog(#"There was an error! %#", error);
}];
}
So I have one Project and many Items, I just dont know how to set up the keyfields so that they save into core data as one project and many items.
So hopefully my code is making sense. If someone could just help me figure out how to save it properly that would be greatly appreciated.

Answer 1

Just set items.project to be equal to the project NSManagedObject you just made
items.project = project;
EDIT: if you have only one project, you should move the Project* project declaration outside of the recivedProData for loop -- you are making one project for every dictionary, and you say you only have one project ever. That entire block of code makes no sense if you have only one project though -- why do you have an array of Project data, and not just one dictionary?

Answer 2

I want to discuss your Core Data model, the one you configured using the Core Data GUI editor. I'm curious about the plurality of the entity named "Items" from the following line of code:
Items *items = [NSEntityDescription insertNewObjectForEntityForName:#"Items" inManagedObjectContext:self.managedObjectContext];
Maybe it's just a matter of semantics. It's possible, however, that the plurality of that entity name indicates a problem in your Core Data model. I'll try to explain, but this is pretty abstract stuff.
Although an entity may have a relationship that represents a collection of things, the entity itself is not really a collection of things; the entity is always a single thing in the model and should be treated as such in your code (and in your naming schemes).
Here's how I would describe your model in words:
The Project entity is a single thing with a relationship called items. The items relationship is a collection (a set) of Item entities (i.e., a one-to-many relationship). But each Item entity is a single thing.
Does your model in the GUI editor reflect this description?