Xcode一致性错误：设置无操作删除规则...是一个高级设置 [英] Xcode consistency error: Setting the No Action Delete Rule... is an advanced setting

问题描述

在Xcode中创建数据模型后，每个对象关系都会抛出以下错误：

After creating a data model in Xcode, it's throwing the following error for each of the object relationships:

Consistency Error:
Setting the No Action Delete Rule on [object relationship] is an advanced setting

什么是Xcode试图告诉我，我该如何回应？

What is Xcode trying to tell me, and how should I respond?

推荐答案

Core Data使用反向关系和删除规则来保持对象图一致

Core Data uses inverse relationships and delete rules to keep the object graph consistent

假设您有A.foo< 1— 1> B.bar和do a.foo = b 。这将自动（有效地）执行 b.bar = a 。

Let's say you have A.foo <1—1> B.bar and do a.foo = b. This automatically (effectively) performs b.bar = a.

您 [b delete] 。使用nullify规则，有效地 b.bar.foo = nil 。使用cascade，它会 [b.bar delete] 。用无动作，它什么也不做; a.foo 现在是一个棘手的核心数据对象引用。

Now let's say you [b delete]. With the "nullify" rule, effectively does b.bar.foo = nil. With "cascade", it does [b.bar delete]. With "no action", it does nothing; a.foo is now a "dangling Core Data object reference".

这不是一个悬挂指针;标准内存管理规则意味着 b 将仍然存在于内存中，而 a 指向它（直到 a 会变成错误），但 a.foo 将永远指向已删除的对象，当您尝试访问它属性。我不知道当您保存并重新获取

It's not really a dangling pointer; standard memory management rules mean that b will still exist in memory while a points to it (until a turns into a fault), but a.foo will forever refer to a deleted object, which raises an exception when you try to access its properties. I'm not sure what happens when you save and re-fetch a either.

- 多关系，它变得更复杂。实现详细信息：此关系似乎是由一个实体拥有，并且仅在实体保存时才会保存（我尝试在不同MOC之间建立关系时遇到此错误：保存的MOC不拥有更新的实体，因此关系从未保存）。显然，当您同时删除 a 和 b 一个假定关系消失，只有一个被删除（但你不知道哪一个！）。

With a many-to-many relationship, it gets more complicated. Implementation details: The relationship appears to be "owned" by one of the entities, and is only saved when that entity is saved (I hit this bug when trying to set up a relationship across different MOCs: the MOC that saved didn't own the updated entity, so the relationship was never saved). Clearly when you delete both a and b, the relationships should also be removed, so one assumes that the relationship disappears only one of them is removed (but you don't know which one!).

你可能想要Nullify或Cascade。我从来不使用Cascade，因为我永远不会记得级联发生在哪个方向。

You probably want Nullify or Cascade. I never use Cascade because I can never remember which direction the cascading happens in.

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