Question

I wrote an ios application in order to save a data to core data and then fetch it with the following code:

   NSManagedObjectContext *context = [self managedObjectContext];
NSError *error;

NSManagedObject *failedBankInfo = [NSEntityDescription
                                   insertNewObjectForEntityForName:@"UserData"
                                   inManagedObjectContext:context];
[failedBankInfo setValue:[NSNumber numberWithInt:1] forKey:@"userId"];

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription
                               entityForName:@"UserData" inManagedObjectContext:context];
[fetchRequest setEntity:entity];
NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
for (NSManagedObject *info in fetchedObjects) {
     NSLog(@"Name: %@", [info valueForKey:@"userId"]);

}

There no problem in here. But After I close my application and modify the setvalue to 2, I only receive the last data which is 2. Earlier data (1) gets deleted.

What should I do to keep the data entries even after I close my application.

Thank You!

Answer 1

You need to create a UIManagedDocument to save the Core Data information. I usually create the UIManagedDocument as a property of the class. For the example I have created a UIManagedDocument called theManagedDocument:

NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
url = [url URLByAppendingPathComponent:@"DocumentName"];

self.theManagedDocument = [[UIManagedDocument alloc] initWithFileURL:url];

if([[NSFileManager defaultManager] fileExistsAtPath:[url path]])
{
    [theManagedDocument openWithCompletionHandler:^(BOOL success){
        if(success) [self documentIsReady];
        if(!success) NSLog(@"Couldn't Open Document");
    }];
}
else 
{
    [theManagedDocument saveToURL:url forSaveOperation:UIDocumentSaveForCreating completionHandler:^(BOOL success){
        if(success) [self documentIsReady];
        if(!success) NSLog(@"Couldn't Create Document");
    }];
}

Then I create a method called documentIsReady that is called when the document has been successfully created or opened (opened if it is already present, created otherwise). I will also keep the context as a property. Here it is called context. I also added in your code:

- (void) documentIsReady
{
    if(self.theManagedDocument.documentState == UIDocumentStateNormal) 
    {
        self.context = self.theManagedDocument.managedObjectContext;
        NSError *error;

        NSManagedObject *failedBankInfo = [NSEntityDescription
                               insertNewObjectForEntityForName:@"UserData"
                               inManagedObjectContext:self.context];
        [failedBankInfo setValue:[NSNumber numberWithInt:1] forKey:@"userId"];

        NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
        NSEntityDescription *entity = [NSEntityDescription
                           entityForName:@"UserData" inManagedObjectContext:self.context];
        [fetchRequest setEntity:entity];
        NSArray *fetchedObjects = [self.context executeFetchRequest:fetchRequest error:&error];
        for (NSManagedObject *info in fetchedObjects) {
            NSLog(@"Name: %@", [info valueForKey:@"userId"]);
        }
    }
}

You will then want to close the document when you are done using:

[self.theManagedDocument closeWithCompletionHandler:^(BOOL success){
    if(success) NSLog(@"Closed Successfully");
    if(!success) NSLog(@"Error Closing Document");
}];