NSFetchRequest doesn't give back anything - objective-c

Question

I am trying to get all the pictures of an album. I am getting this by an webservice. The webservice has the following layout.
{
"name": "Club Brugge - KRC Genk",
"date": "08.10.2012",
"albumId: 1,
"pictures": [
{
"pic_album_id"=1,
"pic_id" = 1,
"url": "http://www.krcgenk.be/images/gallery/album_199/800X600/1a06dc0e405fd0219e3d327f1eec7fbf.jpg"
},
{
"pic_album_id"=1,
"pic_id" = 2,
"url": "http://www.krcgenk.be/images/gallery/album_199/800X600/e8e10c0664eb0533a0534ed69891b165.jpg"
},
{
"pic_album_id"=1,
"pic_id"= 3,
"url": "http://www.krcgenk.be/images/gallery/album_199/800X600/750b55a87b8eae33b8f3278add9bec44.jpg"
}
]
I have the following functions to get all pictures of a certain album.
- (NSMutableArray *)getAllPicturesOfAlbumId: (int)AlbumId
{
NSString *picture_Url = [[NSString alloc]init];
NSArray *results = [[NSArray alloc]init];
_picturesForAlbum = [[NSMutableArray alloc]init];
picture_Url = #"";
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"pic_album_id == %#",
[NSNumber numberWithInt:AlbumId]];
NSLog(#"album id: %#",[NSNumber numberWithInt:AlbumId]);
[request setEntity:[NSEntityDescription entityForName:#"Picture" inManagedObjectContext:self.genkDatabase.managedObjectContext]];
[request setPredicate:predicate];
NSError *error = nil;
results = [self.genkDatabase.managedObjectContext executeFetchRequest:request error:&error];
NSLog(#"results: %#",results);
if (results == nil) {
NSLog(#"nil results");
// handle errors
} else if (results.count == 0) {
NSLog(#"0 results");
// nothing found
} else {
for(int i = 0; i < results.count ; i++){
Picture *picture = [results objectAtIndex:i];
NSLog(#"%#",[results objectAtIndex:i]);
[_picturesForAlbum addObject:picture];
}
}
NSLog(#"%#",_picturesForAlbum);
//NSLog(#"album: %#",[_picturesForAlbum objectAtIndex:5]);
return _picturesForAlbum;
}
The code above, gives the following log. (I gave for testcase AlbumId = 3 with it)
2012-10-12 14:53:04.577 RacingGenk[4793:c07] album id: 3
2012-10-12 14:53:04.578 RacingGenk[4793:c07] results: (
)
2012-10-12 14:53:04.578 RacingGenk[4793:c07] (
)
Hope anybody can help me.
Kind regards.
** Here you see a screenshot of my database model
EDIT
Here you see how I get my pictures and put it in my database.
+ (Picture *)pictureWithGenkInfo:(NSDictionary *)genkInfo
inManagedObjectContext:(NSManagedObjectContext *)context
withAlbumId:(int)albumId
withPictureId:(int)pictureId;
{
Picture *picture = nil;
picture = [NSEntityDescription insertNewObjectForEntityForName:#"Picture"
inManagedObjectContext:context];
picture.url = [genkInfo objectForKey:PICTURES_URL];
picture.pic_album_id = [NSNumber numberWithInt:albumId];
picture.picture_id = [NSNumber numberWithInt:pictureId];
return picture;
}
//The method above is called in my first controller that comes one screen. With this loop I fill up my core data-base.
for (NSDictionary *genkInfo in albums ) {
albumId++;
[Album albumWithGenkInfo:genkInfo inManagedObjectContext:document.managedObjectContext withAlbumId:albumId];
for (NSDictionary *genkInfo2 in pictures ) {
pictureId++;
[Picture pictureWithGenkInfo:genkInfo2 inManagedObjectContext:document.managedObjectContext withAlbumId:albumId withPictureId:pictureId];
}
pictureId = 0;
// table will automatically update due to NSFetchedResultsController's observing of the NSMOC
}

Answer 1

Use predicate
[NSPredicate predicateWithFormat:#"whichAlbum.album_id == %d", AlbumId];
UPDATE
for (NSDictionary *genkInfo in albums ) {
albumId++;
Album *album = [Album albumWithGenkInfo:genkInfo inManagedObjectContext:document.managedObjectContext withAlbumId:albumId];
for (NSDictionary *genkInfo2 in pictures ) {
pictureId++;
Picture *pic = [Picture pictureWithGenkInfo:genkInfo2 inManagedObjectContext:document.managedObjectContext withAlbumId:albumId withPictureId:pictureId];
[album addPictureObject:pic]; // this method should be automatically generated
}
pictureId = 0;
// table will automatically update due to NSFetchedResultsController's observing of the NSMOC
}
// don't forget save context

Answer 2

How to troubleshoot:
Get yourself Liya or another sqlite database viewer. Navigate to the folder with the core data database. On the simulator that would be
/Users/<username>/Library/Application Support/iPhone Simulator/<version of iOS>/Applications/<long cryptig string>/<folder-with-the-core-data-database>
Open the sqlite database, navigate to the ZPicture table and check that data is present.
If there is no data then the the webservice -> core-data program logic has a problem.
If there is data and it appears to be good go back to Xcode and enable logging for the core-data request. Edit the scheme (Product - Edit scheme), select the Run, Debug scheme and change the tab to Arguments. In the field Arguments Passed On Launch add -com.apple.CoreData.SQLDebug 3. Ensure the check box is ticked.
Run your app and in the debugger console window there should be the sql code generated by core-data.
You will see something similar to: (you might see the whichAlbum showing up)
<timestamp> CoreData: annotation: fetch using NSSQLiteStatement <0xfxxxxxx> on entity
'Picture' with sql text 'SELECT 0, t0.Z_PK, t0.Z_OPT, t0.zpic_album_id
FROM zpicture t0 WHERE t0.zpic_album_id == ?'
<timestamp> CoreData: details: SQLite bind[0] = (int64)3
Take the sql command, return to Liya and paste the command into the Run Custom Command field. Replace the question mark in
t0.zpic_album_id == ?
with the album_id you want to see.
The result of the query will be what Core Data will retrieve.
Not sure where the whichAlbum would go. Just come back with your finding and let us know.