关于iPhone：与iOS核心数据的多对多关系

To-Many Relationship with iOS Core Data

我知道有很多与此主题相关的问题，但是我似乎找不到能回答我问题的问题！

我在FactSheet和Image之间有一个关系，如下所示：

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int main(int argc, const char * argv[])
{

@autoreleasepool {
// Create the managed object context
NSManagedObjectContext *context = managedObjectContext();

// Save the managed object context
NSError *error = nil;
if (![context save:&error]) {
NSLog(@"Error while saving %@", ([error localizedDescription] != nil) ? [error localizedDescription] : @"Unknown Error");
exit(1);
}

NSError* err = nil;
NSString* dataPath = [[NSBundle mainBundle] pathForResource:@"FactSheets" ofType:@"json"];
NSArray* FactSheets = [NSJSONSerialization JSONObjectWithData:[NSData dataWithContentsOfFile:dataPath]
options:kNilOptions
error:&err];

[FactSheets enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
FactSheet *factSheet = [NSEntityDescription
insertNewObjectForEntityForName:@"FactSheet"
inManagedObjectContext:context];
factSheet.name = [obj objectForKey:@"name"];
factSheet.details = [obj objectForKey:@"details"];

NSArray* images=[obj objectForKey:@"images"];

[images enumerateObjectsUsingBlock:^(id img, NSUInteger idx, BOOL *stop) {

Image *image = [NSEntityDescription insertNewObjectForEntityForName:@"Image"
inManagedObjectContext:factSheet.managedObjectContext];

image.path = [img objectForKey:@"path"];

if([img objectForKey:@"caption"]!=[NSNull null]) {
image.caption = [img objectForKey:@"caption"];
}

if([img objectForKey:@"label"]!=[NSNull null]) {
image.label = [img objectForKey:@"label"];
}

if([img objectForKey:@"galleryThumb"]!=[NSNull null]) {
image.galleryThumb = [img objectForKey:@"galleryThumb"];
}

[factSheet addImageObject:image];

}];

NSError *error;
if (![context save:&error]) {
NSLog(@"Whoops, couldn't save: %@", [error localizedDescription]);
}
}];

//Test listing
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"FactSheet"
inManagedObjectContext:context];
[fetchRequest setEntity:entity];
NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
for (FactSheet *fs in fetchedObjects) {
NSLog(@"Name: %@", fs.name);
for (Image *i in fs.images) {
NSLog(@"Image Path: %@",i.path);
}
}

}

return 0;
}

运行此方法直到我尝试使用NSLog将其打印出来。它在以下行中断：

1	for (Image *i in fs.images) {

使用"无法识别的选择器发送到实例"错误。当我在SQLite数据库浏览器中打开.sqlite文件时，似乎已按照我的想法插入了数据(尽管我绝不是SQLite专家！)。

我想我的问题是：我是否正确地将对象插入核心数据中，而试图将其打印回-或-我是否应该以其他方式将对象存储到核心数据中？ >

谢谢！

将呼叫更改为此：
for (Image *i in fs.image) {

根据模型，关系名称为image，因此您可以更新模型或循环代码。