Question

我尝试从名为Timeline的CoreData中添加一个包含Tree和User关系的已获取实体。

当我尝试从CoreData中获取它时，一切都很好，存在用户和树，并且没有设置为nil。但是当我将它添加到我的数组时，用户关系会消失，但树不会消失，只有数组中的最后一个Timeline实体保留了两者的引用。

这里是我在json上的循环，我通过id从CoreData获取Timeline，或者如果CoreData在Timeline.get(withJSON:_, inManagedObjectContext:_)内不知道他，则创建它：

var timelines = [Timeline]()
for jsonRow in json.arrayValue {
    if let timeline = Timeline.get(withJSON: jsonRow, inManagedObjectContext: context) {

        print("Timeline entitie from core data :\n", timeline)
        timelines.append(timeline)
    }
}

print("timelines array:\n", timelines)

我在内部循环打印的结果：

Timeline entitie from core data :
 <myApp.Timeline: 0x6080002a1560> (entity: Timeline; id: 0xd0000000046c0006 <x-coredata://D5FDDD6B-2A13-4B03-B592-45C99D801439/Timeline/p283> ; data: {
    createdAt = "2016-12-03 17:25:21 +0000";
    id = 21;
    message = "blablabla";
    tree = "0x60800023fa20 <x-coredata:///Tree/t742495B8-E258-4C42-8E69-AC9776194B7A22>";
    updatedAt = "2016-12-03 17:25:21 +0000";
    url = nil;
    user = "0xd000000000080000 <x-coredata://D5FDDD6B-2A13-4B03-B592-45C99D801439/User/p2>";
}) 


Timeline entitie from core data :
 <myApp.Timeline: 0x6000000bc620> (entity: Timeline; id: 0xd0000000047c0006 <x-coredata://D5FDDD6B-2A13-4B03-B592-45C99D801439/Timeline/p287> ; data: {
    createdAt = "2016-12-04 12:17:23 +0000";
    id = 22;
    message = "jaw dawd awdkj alwkjd alwkjd lawkjd lakwjd lakwjdl kawjl dkajwldkja wlkdjawl kjdawlk jdawlkjaw lkjawlkawjlkw aj lkawjd lkawjd lkjawdl kjawd awdl kajwldk jawlkjd lakwj dlakwj ldkajw lkdjawlk jlakwjd la";
    tree = "0x6000002354c0 <x-coredata:///Tree/t742495B8-E258-4C42-8E69-AC9776194B7A23>";
    updatedAt = "2016-12-04 12:17:23 +0000";
    url = nil;
    user = "0xd000000000080000 <x-coredata://D5FDDD6B-2A13-4B03-B592-45C99D801439/User/p2>";
})

Timeline entitie from core data :
 <myApp.Timeline: 0x6080002a1b60> (entity: Timeline; id: 0xd000000004800006 <x-coredata://D5FDDD6B-2A13-4B03-B592-45C99D801439/Timeline/p288> ; data: {
    createdAt = "2016-12-04 15:19:02 +0000";
    id = 30;
    message = "Niche";
    tree = "0x6080004279e0 <x-coredata:///Tree/t742495B8-E258-4C42-8E69-AC9776194B7A31>";
    updatedAt = "2016-12-04 15:19:02 +0000";
    url = nil;
    user = "0xd000000000080000 <x-coredata://D5FDDD6B-2A13-4B03-B592-45C99D801439/User/p2>";
})

这是我的数组的结果：

timelines array:
 [<myApp.Timeline: 0x6080002a1560> (entity: Timeline; id: 0xd0000000046c0006 <x-coredata://D5FDDD6B-2A13-4B03-B592-45C99D801439/Timeline/p283> ; data: {
    createdAt = "2016-12-03 17:25:21 +0000";
    id = 21;
    message = "blablabla";
    tree = "0x60800023fa20 <x-coredata:///Tree/t742495B8-E258-4C42-8E69-AC9776194B7A22>";
    updatedAt = "2016-12-03 17:25:21 +0000";
    url = nil;
    user = nil;
}), <myApp.Timeline: 0x6000000bc620> (entity: Timeline; id: 0xd0000000047c0006 <x-coredata://D5FDDD6B-2A13-4B03-B592-45C99D801439/Timeline/p287> ; data: {
    createdAt = "2016-12-04 12:17:23 +0000";
    id = 22;
    message = "jaw dawd awdkj alwkjd alwkjd lawkjd lakwjd lakwjdl kawjl dkajwldkja wlkdjawl kjdawlk jdawlkjaw lkjawlkawjlkw aj lkawjd lkawjd lkjawdl kjawd awdl kajwldk jawlkjd lakwj dlakwj ldkajw lkdjawlk jlakwjd la";
    tree = "0x6000002354c0 <x-coredata:///Tree/t742495B8-E258-4C42-8E69-AC9776194B7A23>";
    updatedAt = "2016-12-04 12:17:23 +0000";
    url = nil;
    user = nil;
}), <myApp.Timeline: 0x6080002a1b60> (entity: Timeline; id: 0xd000000004800006 <x-coredata://D5FDDD6B-2A13-4B03-B592-45C99D801439/Timeline/p288> ; data: {
    createdAt = "2016-12-04 15:19:02 +0000";
    id = 30;
    message = "Niche";
    tree = "0x6080004279e0 <x-coredata:///Tree/t742495B8-E258-4C42-8E69-AC9776194B7A31>";
    updatedAt = "2016-12-04 15:19:02 +0000";
    url = nil;
    user = "0xd000000000080000 <x-coredata://D5FDDD6B-2A13-4B03-B592-45C99D801439/User/p2>";
})]

谢谢你得到了答案，六行代码从未让我如此疯狂......

Answer 1

看起来Timeline和User之间的关系是一对一的。在循环中，您为每个Timeline提供相同的User。当你这样做时，它们看起来很好。但由于这种关系是一对一的，因此每次将User分配给新的Timeline时，您也会忽略该关系的先前值。每个User只能有一个Timeline，因此当您将User分配给新Timeline时，旧版本会获得该关系的零值。这就是为什么它是最后一个具有非零值的原因，因为它是唯一一个在下一次循环中不会被改变的原因。

该怎么做取决于您的应用的工作方式。

如果每个User应该只有一个Timeline，请修复您的循环，以便每次分配不同的User。
如果每个User可能有多个Timeline，请将关系修改为User到Timeline之间的多对多。

为什么将coreData实体附加到设置为nil关系的Array？

1 个答案: