Use a subclass of Core Data Entity without storing in Core Data

Question

I have an entity called "Color" that has R,G,B stored, and a subclass that returns saturation, UIColor, etc., as needed. I recently wrote some code where I needed the Color entity to be the Class "Color" so I could call a method on it.

But it seems that broke another part.

Before I store the colors, I use the Color class to figure out what colors to store, based on the methods in the Color class. This is where I'm running into problems.

Color *color = [[Color alloc] initWithColor:[UIColor whiteColor]];
if (color.saturation > 0.2) {
    [self addOrIncrementColor:color];
}

At the if statement, the debugger shows:

color   Color * 0x1f532740
NSManagedObject NSManagedObject 
red CGFloat 0.392157
green   CGFloat 0.443137
blue    CGFloat 0.203922
count   __NSCFNumber *  0x1f559d00
color   UIDeviceRGBColor *  0x200e8f10
saturation  CGFloat 0.539823

However, if I print the description of the Color object, I get:

Color: 0x1f532740 (entity: (null); id: (null) ; data: {})

This of course, passes the color object to the addOrIncrement: method with null info, even though it is set locally.

Any idea how I can get this to work?

score 1 · Accepted Answer · edited May 23 '17 at 10:34

It doesn't look normal to be using NSManagedObjects like you would for normal objects (e.g. with the usual alloc init. Instead, NSManagedObjects should be created with the NSManagedObjectContext.

That being said, if you just want a temporary NSManagedObject that will not be saved to a context, then create them as you would normally, but with a nil context:

NSEntityDescription *entity = [NSEntityDescription entityForName:@"Color" inManagedObjectContext:managedObjectContext];
Color *color = [[Color alloc] initWithEntity:entity insertIntoManagedObjectContext:nil];
if (color.saturation > 0.2) {
    ...
}

Check out this other post for reference.

Use a subclass of Core Data Entity without storing in Core Data

1 Answers1