核心数据:我只想在第一次运行时填充我的数据库

Question

我的方法checkIfExistDatabase第二次运行时必须返回YES，但它返回NO。这是个问题。

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
  [[CoreDataWrapper sharedInstance] checkIfExistDatabase];
  return YES;
}
-(void) checkIfExistDatabase
{
  NSURL *url = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"Mew.sqlite"];
  BOOL isExists = [[NSFileManager defaultManager] fileExistsAtPath:[url absoluteString]];
  if (!isExists) 
  {
   [self populateDatabase];
  }
}
-(void) populateDatabase
{
 NSEntityDescription *entity = [NSEntityDescription entityForName:@"Test" inManagedObjectContext:[self managedObjectContext]]; 
 for (int i =0; i<2; i++) 
 {
    Test *test = [[[Test alloc] initWithEntity:entity insertIntoManagedObjectContext:[self managedObjectContext]] autorelease];
    test.text = @"Text";
    test.index = [NSNumber numberWithInt:i];
 }
 [self saveContext];
}

UPDATE：我添加了applicationDocumentsDirectory方法

- (NSURL *)applicationDocumentsDirectory
{
  return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}

输出：

NSLog(@"absolute string: %@", [url absoluteString]);
absolute string: file://localhost/var/mobile/Applications/6EE4D791-B798-4A2E-83DD-BFA41ED86940/Documents/Mew.sqlite

Answer 1

不要检查实体的存在，检查该实体中的对象（记录）。类似这样的东西：

NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Test" inManagedObjectContext:self.managedObjectContext];
[request setEntity:entity];    
NSError *error = nil;
NSUInteger count = [self.managedObjectContext countForFetchRequest:request error:&error];

如果计数大于0，则表示已填充核心模型实体。

Answer 2

fileExistsAtPath:不是采用路径而不是URL吗？

NSString *file = [[self applicationDocumentsDirectory] stringByAppendingPathComponent:@"Mew.sqlite"];
BOOL isExists = [[NSFileManager defaultManager] fileExistsAtPath:file];