问题
I only just noticed that each uniqueness constraint in CoreData can have multiple attributes (comma,separated,properties). I don't actually know what it does to have multiple attributes in one constraint though. Does it mean that if any of them are unique then the constraint is not broken? The Apple documentation is not particularly helpful:
Constraints: After adding attributes as shown in Configuring Attributes, optionally enter the name of an attribute (or comma-separated list of attributes) to serve as unique constraints on the entity.
来源：https://stackoverflow.com/questions/56285228/how-do-uniqueness-constraints-as-comma-separated-attributes-work-with-swift-in