Adding to created Entities attributes using Magical Record - ios

Question

so I am using Magical Record in my project, and I am attempting to do the following:
- (void)persistNewReadingWithOneA:(NSString *)oneA oneB:(NSString *)oneB{
NSManagedObjectContext *localContext = [NSManagedObjectContext MR_contextForCurrentThread];
FinalRead *reading1A = [FinalRead MR_createInContext:localContext];
reading1A.a1 = oneA;
reading1A.b1 = oneB;
[localContext MR_saveOnlySelfAndWait];
}
As you can see I've persisted with a new entry and now I need to be able to update that same entry by adding to it's attributes. I tried doing the following:
- (void)updateReadingWithTwoA:(NSString *)twoA twoB:(NSString *)twoB{
NSManagedObjectContext *localContext = [NSManagedObjectContext MR_contextForCurrentThread];
FinalRead *reading2A = [FinalRead MR_createInContext:localContext];
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"firstname ==[c] %# AND lastname ==[c] %#"];
FinalRead *finalRead = [FinalRead MR_findFirstWithPredicate:predicate inContext:localContext];
reading2A.a2 = twoA;
reading2A.b2 = twoB;
[localContext MR_saveOnlySelfAndWait];
}
Any Ideas?
EDIT:
I am fetching data from a JSON response like so:
- (void)fetchedData:(NSData *)responseData {
if (self.buttonPressed){
//parse out the json data
NSError* error;
NSArray* json = [NSJSONSerialization
JSONObjectWithData:responseData
options:kNilOptions
error:&error];
NSString *string = [NSString stringWithFormat:#"%#", [json objectAtIndex:0]];
[self persistNewReadingWithOneA:string
oneB:nil];
}else{
//parse out the json data
NSError* error;
NSArray* json = [NSJSONSerialization
JSONObjectWithData:responseData
options:kNilOptions
error:&error];
NSString *string = [NSString stringWithFormat:#"%#", [json objectAtIndex:0]];
[self persistNewReadingWithOneA:nil
oneB:string];
}
}
and then storing to a newly created object like so:
- (void)persistNewReadingWithOneA:(NSString *)oneA oneB:(NSString *)oneB{
NSManagedObjectContext *localContext = [NSManagedObjectContext MR_contextForCurrentThread];
FinalRead *reading1A = [FinalRead MR_createInContext:localContext];
reading1A.a1 = oneA;
reading1A.b1 = oneB;
[localContext MR_saveOnlySelfAndWait];
}
The ViewController then pushes to another that asks another question where once again more JSON is parsed and stored, but into the SAME object that was just created in the previous ViewController. I have the following attributes PER object in NSManagedObject:
#interface FinalRead : NSManagedObject
#property (nonatomic, retain) NSString *a1;
#property (nonatomic, retain) NSString *b1;
#property (nonatomic, retain) NSString *a2;
#property (nonatomic, retain) NSString *b2;
#property (nonatomic, retain) NSString *a3;
#property (nonatomic, retain) NSString *b3;
#property (nonatomic, retain) NSString *a4;
#property (nonatomic, retain) NSString *b4;
#end
So basically, every time that I change a new viewController I'm wanting to add to that same object until the final View has been used.

Answer 1

Your update method also creates a new object:
FinalRead *reading2A = [FinalRead MR_createInContext:localContext];
// ... other stuff
reading2A.a2 = twoA;
reading2A.b2 = twoB;
And the object fetched here:
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"firstname ==[c] %# AND lastname ==[c] %#"];
FinalRead *finalRead = [FinalRead MR_findFirstWithPredicate:predicate inContext:localContext];
is completely unused. In fact I would expect that fetch request to crash, because the
predicate uses %# formats for which no arguments are supplied.
To update an object, you have to fetch it first. And to fetch it you need some
attributes which identify the object that you want to update. For example:
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"firstname ==[c] %# AND lastname ==[c] %#",
firstName, lastName];
FinalRead *finalRead = [FinalRead MR_findFirstWithPredicate:predicate inContext:localContext];
if (finalRead) {
finalRead.a2 = twoA;
finalRead.b2 = twoB;
// ... save context ...
} else {
// no matching object found
}
Update: The solution in your case might be to pass the finalRead object from one
view controller to the next, instead of re-fetching it in each view controller.