Question

我有一个与单位有“多对多”关系的订单。当我尝试按顺序记录单位（NSSet）时，出现错误错误：

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Order" 
                                          inManagedObjectContext:mainContext];
[fetchRequest setEntity:entity];
NSArray *fetchedObjects = [mainContext executeFetchRequest:fetchRequest 
                                                     error:nil];
for (Order *order in fetchedObjects) {

    NSLog(@"%@", [order units]);
    break;
}        
[fetchRequest release];

结果：

Relationship 'units' fault on managed object (0x6d9dd00) <Order: 0x6d9dd00> (entity: Order; id: 0x6d88e40 <x-coredata://97A3F3D5-ABA7-499A-A460-5E25CF49C528/Order/p1> ; data: {
    composition = Hemlock;
    condition = "";
    consignee = "";
    consigneeCompanyName = "";
    contactAlternatePhone = "";
    contactEmail = "";
    contactFirstName = "";
    contactLastName = "";
    contactPhone = "";
    customer = "Havard Empire";
    customerCompanyName = "";
    customerNotes = "";
    dateDue = "1/13/2012 12:00:00 AM";
    dateEntered = "1/6/2012 12:00:00 AM";
    dateOrdered = "1/6/2012 12:00:00 AM";
    deliveryAddress1 = "";
    deliveryAddress2 = "";
    deliveryCity = "";
    deliverySpecialInstructions = "";
    deliveryState = "";
    deliveryZip = "";
    depth = 01;
    detail = "";
    freightRate = "";
    grade = Cull;
    instructionsDirectionsNotes = "";
    lastUpdated = "1/6/2012 3:00:43 PM";
    length = 01;
    location = "Lucedale, ms";
    matsPerLoad = "";
    memoLineNotes = "";
    notes = "";
    orderID = 201205134922479;
    orderNumber = 01062012;
    pUP = Cable;
    pricePerItem = "";
    purchaseOrderNumber = "";
    pushToQuickBooks = True;
    quantity = 0;
    quickbooksCompany = 1;
    salesman = "Accounting Adj";
    separateRate = False;
    taxRate = "";
    totalLoads = "";
    type = "2ply Mat";
    units = "<relationship fault: 0x6dacf20 'units'>";
    vendorID = 10;
    width = 01;
})

不打印单位。它说"<relationship fault: 0x6dacf20 'units'>";

另外，为什么在我只需要单位时打印整个对象？

Answer 1

这不是错误 - 它是Core Data的一个名为'faulting'的功能。这是Apple的description：

Faulting可减少应用程序消耗的内存量。一个   fault是占位符对象，表示托管对象   还没有完全实现，或者是一个集合对象   代表一种关系：

托管对象错误是相应类的实例，但是   它的持久变量尚未初始化。关系错误   是集合类的子类，表示   关系。错误允许核心数据在边界上设置边界   对象图。由于未实现故障，因此管理对象发生故障   消耗较少的内存，而不是与故障相关的管理对象   需要在记忆中表现出来。

如果要查看每个Unit对象，则必须专门访问它们。请尝试以下方法：

for (Order *order in fetchedObjects) {
    for (Unit *unit in [order units]) {
       NSLog(@"%@", unit);
       //I am not at a computer, so I cannot test, but this should work. You might have to access each property of the unit object to fire the fault, but I don't believe that is necessary.
    }
}

Answer 2

为了查看“to-many”关系的所有对象，您可以使用 allObjects 关系的方法NSSet。

在您的具体情况下，打印fetchedObjects中第一个订单的所有单位的代码将如下所示：

for (Order *order in fetchedObjects) { NSLog(@"%@", [order.units allObjects]); break; }

Answer 3

在Swift中它会是这样的：

for order in fetchedObjects {
    for unit in order.units.allObjects as [Unit] {
        println(unit)
    }
}

Answer 4

是的，我也有同样的问题。尝试只打印此表的某些字段，例如：

    for(Category *category in fetchedObjects) 
    {
        for(Cards *card in category.cards) 
        {
            NSLog(@"Question %@", card.question);
            NSLog(@"Card %@", card);
        }
    }

Answer 5

这非常直观。我抓了大约一整天，直到我意识到我无法打印整个NSSet对象或集合中的每个NSManagedObject，如下所示：

for (Order *order in fetchedObjects) {
   for (Unit *unit in [order units]) {
      NSLog(@"%@", unit);
   }
}

这会在xcode中产生错误..但是如果我打印出每个NSMangedObject中的每个属性，那就没问题了。我猜Apple对自动加载多对象有内存关注。在存在多对多关系的情况下，它将消耗大量内存。所以需要延迟加载每个属性。

for (Order *order in fetchedObjects) {
   for (Unit *unit in [order units]) {
      NSLog(@"Unit Name : %@", unit.name);
   }
}

这将打印出单位名称..

CoreData关系错误？

5 个答案: