Fetching data in core data - ios

Question

I have Three tables, One to many relationship between Session and Album , One to many relationship between Album to songs , When I tried to fetch data from songs Then I get nothing
Here is my readFRomDB func
-(void)readDataFromDB{
AppDelegate *delegates = (AppDelegate *) [[UIApplication sharedApplication] delegate];
self.managedObjectContext = [delegates managedObjectContext];
if (runningSessionArray.count > 0) {
[runningSessionArray removeAllObjects];
}
NSManagedObjectContext *moc = [self managedObjectContext];
NSArray *searchResults = nil;
NSArray *searchAlbumsResults = nil;
NSArray *searchSongsResult=nil;
NSFetchRequest * fetchRequest1 = [[NSFetchRequest alloc] init];
NSFetchRequest * fetchRequest2 = [[NSFetchRequest alloc] init];
NSEntityDescription *entityDescription = [NSEntityDescription
entityForName:#"RunningSession" inManagedObjectContext:moc];
NSFetchRequest *requestData = [[NSFetchRequest alloc] init];
[requestData setEntity:entityDescription];
[requestData setFetchLimit:1] ;
NSError *error;
// if get a entity, that means exists, so fetch it.
searchResults = [managedObjectContext executeFetchRequest:requestData error:&error];
for ( RunningSession *session in searchResults) {
// Update the Records
self.runnningSessionId=[NSString stringWithFormat:#"%#",session.runningSessionID];
self.title=session.title;
self.desc=[NSString stringWithFormat:#"%#",session.desc];
[fetchRequest1 setEntity:[NSEntityDescription entityForName:#"Albums"
inManagedObjectContext:session.managedObjectContext]];
[fetchRequest1 setEntity:entityDescription];
[fetchRequest1 setFetchLimit:1] ;
searchAlbumsResults = [session.managedObjectContext executeFetchRequest:fetchRequest1 error:&error];
NSMutableArray *tagNamesArray = [[NSMutableArray alloc] init];
//NSLog(#"Local Discount Shops:%#",discounts.shops);
NSSet *tagA = session.albums;
if (tagA.count>0) {
for (Albums *tag in tagA
) {
// NSLog(#"tag:%#",tag);
NSString *albumID;
NSString *aTitle;
NSString *aPrice;
NSString *aDuration;
NSString *aUrl;
NSString *aPurchasedHtml;
NSString *aNonPurchasedHtml;
if (tag.albumID != NULL) {
albumID = [NSString stringWithFormat:#"%#",tag.albumID]; //tag.shopId;
}else{
albumID = #"";
}
if (tag.title != NULL) {
aTitle = tag.title;
}
else{
aTitle = #"";
}
if (tag.price != NULL) {
aPrice = tag.price;
}
else{
aPrice = #"";
}
if (tag.duration != NULL) {
aDuration = tag.duration;
}
else{
aDuration = #"";
}
if (tag.url != NULL) {
aUrl = tag.url;
}
else{
aUrl = #"";
}
if (tag.purchasedHtml != NULL) {
aPurchasedHtml = tag.purchasedHtml;
}
else{
aPurchasedHtml = #"";
}
if (tag.nonPurchasedHtml != NULL) {
aNonPurchasedHtml = tag.nonPurchasedHtml;
}
else{
aNonPurchasedHtml = #"";
}
NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:albumID,#"Id",aTitle,#"Title",aPrice,#"Price", aDuration,#"Duration",
albumUrl,#"Url",aPurchasedHtml,#"PurchasedItemsHtml",aNonPurchasedHtml,#"NonPurchasedItemsHtml", nil];
[tagNamesArray addObject:dict];
NSLog(#"tag.shop:%#",tag.songs);
[fetchRequest2 setEntity:[NSEntityDescription entityForName:#"Songs"
inManagedObjectContext:tag.managedObjectContext]];
[fetchRequest2 setEntity:entityDescription];
[fetchRequest2 setFetchLimit:1];
searchSongsResult = [tag.managedObjectContext executeFetchRequest:fetchRequest2 error:&error];
NSMutableArray *songsNamesArray = [[NSMutableArray alloc] init];
//NSLog(#"Local Discount Shops:%#",discounts.shops);
NSSet *tags = tag.songs;
if (tags.count>0) {
for (Songs *tag in tags) {
// NSLog(#"tag:%#",tag);
NSString *sID;
NSString *sTitle;
NSString *startTime;
if (tag.songsId !=NULL) {
sID = [NSString stringWithFormat:#"%#",tag.songsId]; //tag.shopId;
}else{
sID = #"";
}
if (tag.title != NULL) {
sTitle = tag.title;
}
else{
sTitle = #"";
}
if (tag.startTime != NULL) {
startTime = tag.startTime;
}
else{
startTime = #"";
}
NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:sID,#"Id",sTitle,#"Title",startTime,#"Duration", nil];
[songsNamesArray addObject:dict];
}
}
NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:albumID,#"Id",albumTitle,#"Title",albumPrice,#"Price",albumDuration,#"Duration",albumUrl,#"Url",albumPurchasedHtml,#"PurchasedItemsHtml",albumNonPurchasedHtml,#"NonPurchasedItemsHtml",songsNamesArray,#"Songs", nil];
}
}
// NSPredicate *bobPredicate = [NSPredicate predicateWithFormat:#"firstName = 'Bob'"];
// NSLog(#"Bobs: %#", [discounts filteredArrayUsingPredicate:bobPredicate]);
NSMutableArray *albumArray = [[NSMutableArray alloc] init];
albumArray = [tagNamesArray mutableCopy];
NSDictionary* dict = [NSDictionary dictionaryWithObjectsAndKeys:self.runnningSessionId,#"Id",title,#"Title",self.title,#"title",self.desc,#"Description",albumArray,#"Albums", nil];
[self.runningSessionArray addObject:dict];
// [self StudentDiscountData];
// NSLog(#"studentDataArray:%#",self.studentDataArray);
}
NSLog(#"RunningSession: %#",self.runningSessionArray);
}

Answer 1

I think you don't need to all those steps getting session data is enough and from that you can get Albums list as you set the one to many relationship. And from each Album you will get Songs
AppDelegate *delegates = (AppDelegate *) [[UIApplication sharedApplication] delegate];
self.managedObjectContext = [delegates managedObjectContext];
if (runningSessionArray.count > 0) {
[runningSessionArray removeAllObjects];
}
NSManagedObjectContext *moc = [self managedObjectContext];
NSArray *searchResults = nil;
NSArray *searchAlbumsResults = nil;// not required
NSArray *searchSongsResult=nil;//not required
NSFetchRequest * fetchRequest1 = [[NSFetchRequest alloc] init];//not required
NSFetchRequest * fetchRequest2 = [[NSFetchRequest alloc] init];//not required
NSEntityDescription *entityDescription = [NSEntityDescription
entityForName:#"RunningSession" inManagedObjectContext:moc];
NSFetchRequest *requestData = [[NSFetchRequest alloc] init];
[requestData setEntity:entityDescription];
[requestData setFetchLimit:1] ;
NSError *error;
// if get a entity, that means exists, so fetch it.
searchResults = [managedObjectContext executeFetchRequest:requestData error:&error];
//This returns array of sessions
for ( RunningSession *session in searchResults) {
NSArray *albumsArray = session.albums; //This returns Albums list as you set one to many relation
for ( Album *album in albumsArray) {
NSArray *songsArray = album.songs; //This returns songs list as you set one to many relation
}
}