Initialization wrong class - ios

Question

i class
Collections *tempLocalCollection = [[Collections alloc] init];
the problem is that when I try to promote an attribute in sequent way
tempLocalCollection.id = [f numberFromString:[NSString stringWithFormat:#"%#", #"0"]];
tempLocalCollection.action = #"client_insert";
I should be in error
-[Collections setId:]: unrecognized selector sent to instance 0xff8afb0 2015-09-16 10:25:14.235 App[1042:128375] ***
Terminating app due to uncaught exception
'NSInvalidArgumentException', reason: '-[Collections setId:]:
unrecognized selector sent to instance 0xff8afb0'
where am I wrong ?
Collections.h
#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>
#class Items;
#interface Collections : NSManagedObject
#property (nonatomic, retain) NSNumber * datetime_creation;
#property (nonatomic, retain) NSNumber * datetime_last_update_client;
#property (nonatomic, retain) NSNumber * datetime_last_update_server;
#property (nonatomic, retain) NSString * local_delete;
#property (nonatomic, retain) NSNumber * id;
#property (nonatomic, retain) NSString * action;
#property (nonatomic, retain) NSString * label;
#property (nonatomic, retain) NSString * labelServer;
#property (nonatomic, retain) NSNumber * ref_user;
#property (nonatomic, retain) NSNumber * sorting;
#property (nonatomic, retain) NSNumber * system;
#property (nonatomic, retain) NSSet *collection_item;
#end
#interface Collections (CoreDataGeneratedAccessors)
#end
Collections.m
#import "Collections.h"
#import "Items.h"
#implementation Collections
#dynamic datetime_creation;
#dynamic datetime_last_update_client;
#dynamic datetime_last_update_server;
#dynamic local_delete;
#dynamic action;
#dynamic id;
#dynamic label;
#dynamic labelServer;
#dynamic ref_user;
#dynamic sorting;
#dynamic system;
#dynamic collection_item;
#end
This is the method that uses the class and where it goes wrong.
I think the context is the same right?
-(Collections *) upgrateListCollection:(NSDictionary *) coll{
NSNumberFormatter *f = [[NSNumberFormatter alloc] init];
f.numberStyle = NSNumberFormatterDecimalStyle;
NSNumber *id = [f numberFromString:[NSString stringWithFormat:#"%#", coll[#"id"]]];
Collections *tempLocalCollection = [[Collections alloc] init];
NSArray *tmp = [Collections MR_findByAttribute:#"id" withValue:id];
if(tmp.count != 0){
tempLocalCollection = tmp[0];
}
if(!tempLocalCollection.isAccessibilityElement){
tempLocalCollection.id = [f numberFromString:[NSString stringWithFormat:#"%#", #"0"]];
tempLocalCollection.action = #"client_insert";
}else{
if([tempLocalCollection.local_delete isEqual: #"1"]){
tempLocalCollection.action = #"client_delete";
}else{
if([tempLocalCollection.label isEqual:coll[#"label"]]){
if(tempLocalCollection.datetime_last_update_client < coll[#"datetime_last_update_server"]){
tempLocalCollection.action = #"client_update";
}else{
tempLocalCollection.action = #"server_update";
}
}
}
}
if(tempLocalCollection != nil){
tempLocalCollection.labelServer = coll[#"label"];
tempLocalCollection.datetime_last_update_server = coll[#"datetime_last_update_server"];
tempLocalCollection.datetime_creation = coll[#"creation_utc_server"];
}
return tempLocalCollection;
}

Answer 1

NSManagedObject subclass (Collections) properties are dynamic, their setter and getter are generated at runtime
Thus when you create object of Collections using alloc/init in that case the dynamic properties are not created hence you get the exception unrecognized selector sent to instance
The right way of creating a NSManagedObject is
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Collections" inManagedObjectContext:myMOC];
Collections *collection = (Collections *)[[NSManagedObject alloc] initWithEntity:entity insertIntoManagedObjectContext:myMOC];
And if you want to create a temporary object of Collections then pass nil as manage object context
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Collections" inManagedObjectContext:myMOC];
Collections *tempObj = (Collections *)[[NSManagedObject alloc] initWithEntity:entity insertIntoManagedObjectContext:nil];

Answer 2

That is a managed object and needs to be created in its managing context.