Question

我有三张桌子，会话和专辑之间的一对多关系，专辑与歌曲之间的一对多关系，当我试图从歌曲中获取数据然后我什么都没得到

这是我的readFRomDB函数

- （无效）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

我认为您不需要所有这些步骤来获取会话数据就足够了，因此您可以在设置一对多关系时获取相册列表。从每个专辑中你将获得歌曲

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
   }
}

获取核心数据中的数据

1 个答案: