ios - 无法处理 executeFetchRequest 错误

Question

我的提取请求工作正常，我可以毫无问题地获取我提取的对象。我想做的是在实体不存在的情况下处理错误。问题是，我无法处理错误，因为当我调用 executeFetechRequest: error: 时应用程序崩溃，没有任何警告。

我的提取看起来像:

NSManagedObjectContext *context = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];

NSFetchRequest *request = [[NSFetchRequest alloc] init];
request.entity = [NSEntityDescription entityForName:@"Info" inManagedObjectContext:context];
request.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"infoID" ascending:YES]];
[request setReturnsObjectsAsFaults:NO];

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"infoID like %@",[a substringFromIndex:13]];
request.predicate = predicate;
request.fetchBatchSize = 1;

NSError *error = nil;

NSArray *results = [context executeFetchRequest:request error:&error];

if (error == nil) {
    ...
}
else {
    //handle error
}

正如我所说，只要实体存在就没有问题，但如果它不存在，我想处理错误。任何想法？干杯

Answer 1

您可以询问模型是否存在这样的实体:

    NSArray *entities = managedObjectModel.entities;
    BOOL canExecute=NO;
    for(NSEntityDescription *ed in entities) {
       // check if entity name is equal to the one you are looking for
       if(found) {
          canExecute=YES;
          break;
       }
    }

   if(canExecute) {
     // execute your request and all the rest...
   } else {
     NSLog(@"Entity description not found");
   }

如果不存在则不执行获取请求