Difference between NSEntityDescription creation methods

Question

What is the difference, in terms of outcome, between the 2 following methods:

+ (id)insertNewObjectForEntityForName:(NSString *)entityName inManagedObjectContext:(NSManagedObjectContext *)context;

+ (NSEntityDescription *)entityForName:(NSString *)entityName inManagedObjectContext:(NSManagedObjectContext *)context;

When should I use each one of them?

Answer 1

insertNewObjectForEntityForName creates an instance of the entity and adds it to the context. The context is now dirty and needs to be saved. The returned instance is a subclass of NSManagedObject.

entityForName returns the NSEntityDescription instance which describes the entity, what attributes and relationships it has, how they are constructed. The context is not modified in any way.

Answer 2

insertNewObjectForEntityForName:... returns NSManangedObject object which is same as below code.

NSManagedObjectModel *managedObjectModel =
        [[context persistentStoreCoordinator] managedObjectModel];
NSEntityDescription *entity =
        [[managedObjectModel entitiesByName] objectForKey:entityName];
NSManagedObject *newObject = [[NSManagedObject alloc]
            initWithEntity:entity insertIntoManagedObjectContext:context];
return newObject;

entityForName:.. returns NSEntityDescription object which is same as below code.

NSManagedObjectModel *managedObjectModel = [[context persistentStoreCoordinator] managedObjectModel]; 
NSEntityDescription *entity = [[managedObjectModel entitiesByName] objectForKey:entityName]; 
return entity;

Answer 3

The id variable is a data type that represents an object’s address. Because it’s just an address, id can be any object, and because its type is a pointer,you don’t need to include the * symbol

+ (id)insertNewObjectForEntityForName:(NSString *)entityName inManagedObjectContext:(NSManagedObjectContext *)context;

As the * symbol signifies a pointer to a specific type.

+ (NSEntityDescription *)entityForName:(NSString *)entityName inManagedObjectContext:(NSManagedObjectContext *)context;