Fetching the Objects from two different entities

Question

In my project I'm entering the same objects in two different Entities in the same data model with same MOC and Persistence Store. I don't want to duplicate the entity because I'm going to modify (remove) objects from the first entity. My question is How I'm going to fetch the objects form another entity? DO I need to have different persistence store and MOC? Well I already fetched the objects but its giving me null value and crashed telling that object can not be nil value.

I guess values are not saving in the core data. Following is the line of code I used to store the values in coreData

CommonEvent *commonEvent = (CommonEvent *)[NSEntityDescription insertNewObjectForEntityForName:@"CommonEvent" inManagedObjectContext:_managedObjectContext];


[commonEvent setValue:number forKey:@"commonNumber"];
[commonEvent setValue:name forKey:@"commonName"];

following is the line of code to fetch the data form core data

CommonEvent *event;

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"CommonEvent" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];

// define a sort descriptor
NSSortDescriptor *nameDescriptor = [[NSSortDescriptor alloc]initWithKey:@"commonName" ascending:YES];
NSSortDescriptor *numberDescriptor = [[NSSortDescriptor alloc]initWithKey:@"commonNumber" ascending:YES];



NSArray *scArray = [[NSArray alloc]initWithObjects:nameDescriptor,numberDescriptor, nil];


// give sort descriptor array to the fetch request
fetchRequest.sortDescriptors = scArray;

// fetch all objects
NSError *error = nil;
NSArray *fetchedObjects = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];

if (fetchedObjects == nil) {
    NSLog(@" we have a problem: %@", error);
}

NSMutableArray *mutableArray = [[NSMutableArray alloc]init];
NSLog(@" %@  %@  for index:%d", [event.commonNumber description],[event.commonName description], indexPath.row);  // It shows that object values are null


// display all objects
for (CommonEvent *event in fetchedObjects) {

    [mutableArray addObject:[event.commonNumber description]];
    //
     NSLog(@" %@  %@  for index:%d", [event.commonNumber description],[event.commonName description], indexPath.row);
}

Your question is very hard to understand. But, I don't see any call to save data anywhere in the code you posted. — Tom Harrington, Jul 15 '13 at 16:55
Sorry about that... I'm saving my data in a core data by using following code. CommonEvent *commonEvent = (CommonEvent *)[NSEntityDescription insertNewObjectForEntityForName:@"CommonEvent" inManagedObjectContext:_managedObjectContext]; [commonEvent setValue:number forKey:@"commonNumber"]; [commonEvent setValue:name forKey:@"commonName"]; — GameBegins, Jul 15 '13 at 16:59
You included that in your question, but that does not save any data. To save data with Core Data you need to call `-[NSManagedObjectContext save:]`. — Tom Harrington, Jul 15 '13 at 17:04

Mundi · Answer 1 · 2013-07-15T18:43:39.853

You have to save your data after inserting it into the MOC:

NSError *error;
[_managedObjectContext save:&error];

Also, why are you using key-value coding when you already have created NSManagedObject subclasses? You can write with dot notation and avoid errors:

commonEvent.commonNumber = number;
commonEvent.commonName = name;

Also, in your code you are declaring event and never initialize it. Of course it will be nil. You probably intended to use the fetched results, e.g.

CommonEvent *event = fetchedObjects.count ? fetchedObjects[0] : nil;

Your code will be easier to read if you make it more concise:

NSFetchRequest *request = 
    [NSFetchRequest fetchRequestWithEntityName:@"CommonEvent"];
request.sortDescriptors = @[
  [NSSortDescriptor sortDescriptorWithKey:@"commonName" ascending:YES],
  [NSSortDescriptor sortDescriptorWithKey:@"commonNumber" ascending:YES]];
NSError *error;
NSArray *fetchedObjects = [_managedObjectContext executeFetchRequest:request
                           error:&error];

Fetching the Objects from two different entities

1 Answers1