Question

Apologies if this has been answered before but I can’t find a reference. I am trying Cocoa / obj-c for the first time. I am trying to knock up an app which will sync with a remote backup system via http (a la s3) and am stumbling around some fundamental core data issues.

I have created an entity and can invoke this without issues. The problem arrives when I call save on NSManagedObjectContext.

I am not going to include all methods involved in invoking the object context / model as the log output should (I think) verify that it is working as expected.

Best described with code and appropriate log entries.

---

*First, for illustration, I am invoking the managed object: *

- (NSManagedObjectModel *)managedObjectModel {

    if (managedObjectModel != nil) {
        return managedObjectModel;
    }

    managedObjectModel = [[NSManagedObjectModel mergedModelFromBundles:nil] retain];    
    NSLog(@"The managed object model is defined as follows:\n%@",     managedObjectModel);
    return managedObjectModel;
}

And the log output from the above NSLog:

2011-09-06 14:31:38.322 TryAgain[18885:a0f] The managed object model is defined as follows:
(<NSManagedObjectModel: 0x2000e2b00>) isEditable 1, entities {
        BackupItinerary = "(<NSEntityDescription: 0x20020e9e0>) name BackupItinerary, managedObjectClassName NSManagedObject, renamingIdentifier 
            BackupItinerary, isAbstract 0, superentity name (null), properties {\n    \"file_url\" = \"(<NSAttributeDescription: 0x2000faec0>), name
            file_url, isOptional 0, isTransient 0, entity BackupItinerary, renamingIdentifier file_url, validation predicates (\\n), warnings (\\n),
            versionHashModifier (null), attributeType 700 , attributeValueClassName NSString, defaultValue (null)\";\n    \"last_sync_date\" =
            \"(<NSAttributeDescription: 0x2000faf60>), name last_sync_date, isOptional 1, isTransient 0, entity BackupItinerary, renamingIdentifier
            last_sync_date, validation predicates (\\n), warnings (\\n), versionHashModifier (null), attributeType 900 , attributeValueClassName
            NSDate, defaultValue (null)\";\n}, subentities {\n}, userInfo {\n}, versionHashModifier (null)";
}, fetch request templates {
}

This looks so have been successful. No exceptions thrown, or warnings.

Now, the actual problem arrives when I call save on the object context. I have a NSOpenPanel which allows for picking dir / files to backup (all hooked up and working fine). Upon the user selecting a dir/file I want to set the value, so I:

NSArray *paths = [panel URLs];
NSURL *filePath = [paths objectAtIndex:0];
[directories addObject:filePath];
[directories setArray:[[NSSet setWithArray: directories] allObjects]];  
NSEntityDescription *BackupItineraryEntity = [[self.managedObjectModel  entitiesByName] objectForKey:@"BackupItinerary"];
NSManagedObject* BackupItinerary = [[NSManagedObject alloc]
                    initWithEntity:BackupItineraryEntity
    insertIntoManagedObjectContext:self.managedObjectContext];
[BackupItinerary setValue:[filePath absoluteString] forKey:@"file_url"];
NSLog(@"entity:\n%@", BackupItinerary);

And the call to NSLog says (having selected /Users/rick/selenium2-webdriver/):

2011-09-06 14:31:38.328 TryAgain[18885:a0f] entity:
<NSManagedObject: 0x200216c80> (entity: BackupItinerary; id: 0x200090860 <x-coredata:///BackupItinerary/t0C005B39-D185-454B-B364-31314EEB10F02> ;     
        data: {
            "file_url" = "file://localhost/Users/rick/selenium2-webdriver/";
            "last_sync_date" = nil;
        })

So, the file_url seems to be populated then, yes? But when I:

NSError *error;
if (![[self managedObjectContext] save:&error]) {
    NSLog(@"Unresolved error %@, %@, %@", error, [error userInfo],[error localizedDescription]);
}

The log says:

2011-09-06 14:31:38.330 TryAgain[18885:a0f] Unresolved error Error Domain=NSCocoaErrorDomain Code=1570 UserInfo=0x2000cc4e0 "file_url is a required  
value.", {
    NSLocalizedDescription = "file_url is a required value.";
    NSValidationErrorKey = "file_url";
    NSValidationErrorObject = "<NSManagedObject: 0x20020f660> (entity: BackupItinerary; id: 0x20008faa0 <x-coredata:///BackupItinerary/t0C005B39
            D185-454B-B364-31314EEB10F03> ; data: {\n    \"file_url\" = nil;\n    \"last_sync_date\" = nil;\n})";
}, file_url is a required value.

---

So basically:

I can, it seems (?), invoke the an entity and set a value on it, but when it comes to saving it the values is not set. The above code is executed inline and I am using garbage collection.

Feels like a total newb school boy error issue but for the life of me I can’t see what I am missing having gone over the docs, highlevel tutorials and example code.

Pointers appreciated!

Answer 1

You are looking at two different managed object instances. The instance that has its file_url property set is <NSManagedObject: 0x200216c80> while the one that reports the error is <NSManagedObject: 0x20020f660>.

Somewhere, you are inserting an instance but not giving it a file_url value. In the code given, it might happen if the user selects cancel in the NSOpenPanel.