在Core Data中创建动态模式？ [英] Faking a dynamic schema in Core Data?
问题描述
通过阅读Core Data上的Apple文档，我了解到当您需要动态模式时，您不应该使用Core Data。如果我想为用户提供创建自己的属性的能力，在核心数据模型中，如果我创建了一些虚拟属性，如自定义十进制1，自定义十进制2，自定义文本1 自定义文本2等，用户可以命名和使用为自己的目的？
From reading the Apple Docs on Core Data, I've learned that you should not use Core Data when you need a dynamic schema. If I wanted to provide the user the ability to create their own properties, in a core data model would it work if I created some "dummy" attributes like "custom decimal 1", "custom decimal 2", "custom text 1", "custom text 2" etc that the user could name and use for their own purposes?
显然，这将不适用于关系，但对于简单的属性，它似乎是一个合理的解决方法。在我的实体上创建一堆虚拟属性，大多数用户未使用会明显降低它们的性能？你有任何人试过这样的东西吗？感谢！
Obviously this won't work for relationships, but for simple properties it seems like a reasonable workaround. Will creating a bunch of dummy attributes on my entities that go unused by most users noticeably decrease performance for them? Have any of you tried something like this? Thanks!
推荐答案
首先，请参阅核心数据文档关系。使用您的示例，考虑如下：
First, see the Core Data docs on relationships. Using your example, consider something like:
- 一个CarAttributeType实体，名称为weight in pounds
- 一个CarAttribute实体，其值为2765.
- 一个Car实体，具有您提到的所需值（如color，make
然后，在CarAttribute和CarAttributeType之间有多对一的关系（许多CarAttribute可以有相同的类型） Car和CarAttribute之间的多对多关系（每辆车可以有很多属性）。此解决方案比硬编码的NULL字段设置要复杂一些。但是，它避免了重复群组，希望更容易维护。
Then, have a many-to-one relationship between CarAttribute and CarAttributeType (many CarAttributes can have the same type), a one-to-many relationship between Car and CarAttribute (each car can have many attributes). This solution is a bit more complicated to setup than the hard-coded NULL fields. However, it avoids repeating groups and is hopefully more maintainable.
编辑：是的，我错过了。我想你会想要一个StringCarAttribute，StringCarAttributeType，FloatCarAttribute，FloatCarAttributeType等。然后，在StringCarAttribute和StringCarAttributeType之间有一个多对一，等等。Car将有一个到manys与StringCarAttribute和FloatCarAttribute。多个类型实体的原因是你没有一个StringCarAttribute和FloatCarAttribute，都声明自己使用一个权重属性类型。
Yes, I missed that. I think you would want a StringCarAttribute, StringCarAttributeType, FloatCarAttribute, FloatCarAttributeType, etc. Then, have a many-to-one between StringCarAttribute and StringCarAttributeType, etc. Car will have one-to-manys with both StringCarAttribute and FloatCarAttribute. The reason for multiple type entities is so you don't have a StringCarAttribute and FloatCarAttribute, both declaring themselves to be using a single weight attribute type.
有一个CarAttribute与所有类型违反1NF＃4。
Having one CarAttribute with all the types goes against 1NF #4.
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