How to convert NSObject model class to a sub-class of NSManagedObject? - ios

Question

I have this simple model class that represent rss article called RSSEntry.
Now I want to start working wit core data with this model class, but I didn't create the project with the 'use core data' checkbox checked.
this is the class:
#import <Foundation/Foundation.h>
#interface FRSSEntry : NSObject{
NSString *_blogTitle;
NSString *_articleTitle;
NSString *_articleUrl;
NSDate *_articleDate;
NSString *_articleImageUrl;
NSString *_content;
}
#property (copy) NSString *blogTitle;
#property (copy) NSString *articleTitle;
#property (copy) NSString *articleUrl;
#property (copy) NSDate *articleDate;
#property (copy) NSString *articleImageUrl;
#property (copy) NSString *content;
- (id)initWithBlogTitle:(NSString*)blogTitle articleTitle:(NSString*)articleTitle articleUrl:(NSString*)articleUrl articleDate:(NSDate*)articleDate articleImageUrl:(NSString *)imageUrl andContent:(NSString *)content;
#end
the implementations is:
#import "FRSSEntry.h"
#implementation FRSSEntry
#synthesize blogTitle = _blogTitle;
#synthesize articleTitle = _articleTitle;
#synthesize articleUrl = _articleUrl;
#synthesize articleDate = _articleDate;
#synthesize articleImageUrl = _articleImageUrl;
#synthesize content = _content;
- (id)initWithBlogTitle:(NSString*)blogTitle articleTitle:(NSString*)articleTitle articleUrl:(NSString*)articleUrl articleDate:(NSDate*)articleDate articleImageUrl:(NSString *)imageUrl andContent:(NSString *)content
{
if ((self = [super init])) {
_blogTitle = [blogTitle copy];
_articleTitle = [articleTitle copy];
_articleUrl = [articleUrl copy];
_articleDate = [articleDate copy];
_articleImageUrl = [imageUrl copy];
_content = [content copy];
}
return self;
}
#end
very simple. Now how do I convert it so I can use it as a core data entity?

Answer 1

So to transform your model class into an NSManagedObject subclass you have to remove the instance variable declarations. Then replace all your #synthesize statements with #dynamic. This tells the compiler that CoreData will provide the implementation for those properties so it can do it's magic there. The custom initializer you have then also needs to be removed because NSManagedObject objects are initialized in a different way.
The code would look something like
#import <Foundation/Foundation.h>
#interface FRSSEntry : NSManagedObject
#property (copy) NSString *blogTitle;
#property (copy) NSString *articleTitle;
#property (copy) NSString *articleUrl;
#property (copy) NSDate *articleDate;
#property (copy) NSString *articleImageUrl;
#property (copy) NSString *content;
#end
-
#import "FRSSEntry.h"
#implementation FRSSEntry
#dynamic blogTitle;
#dynamic articleTitle;
#dynamic articleUrl;
#dynamic articleDate;
#dynamic articleImageUrl;
#dynamic content;
#end
You usually initialize them with something like
// Get the entity description
NSEntityDescription *entityDescription = [NSEntityDescription entityForName:#"FRSSEntry" inManagedObjectContext:context];
// Insert a new YourModelObject into the context
ReceivedMessage *newMessage = [[FRSSEntry alloc] initWithEntity:entityDescription insertIntoManagedObjectContext:context];
You could have a custom initializer but you would have to call [super initWithEntity:entityDescription insertIntoManagedObjectContext:context]. The initializer would get really long with all this parameters so I suggest you just set each property once you have the object initialized.
Judging from your response, you have just begun CoreData integration. Creating an NSManagedObject subclass is just a tip of the iceberg when working with core data. CoreData is a big an complex framework so I suggest you start by reading https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/CoreData/cdProgrammingGuide.html. Stack Overflow is also full of questions and great answers on this topic.
Another thing I suggest you look into is MagicalRecord. It's a great library that makes some of the tedious tasks very simple: https://github.com/magicalpanda/MagicalRecord