核心数据 - 使用keypath和Object ID获取对象

I would like to fetch my data from Core Data, where the books assigned to the person "Max". For this, I have the following code:

我想从Core Data中获取我的数据,其中分配给“Max”的人的书籍。为此,我有以下代码:

  let request = NSFetchRequest<Book>(entityName: "Book")
    request.predicate = NSPredicate(format: "person.firstName = %@", "Max")
    do {
       let books = try context.fetch(request)
       for x in 0 ..< books.count {
          print(books[x].name)
       }
    } catch { }

But now I would like to fetch the data where the books are assigned to a person with the Object ID "xyz".

但是现在我想获取将书籍分配给对象ID为“xyz”的人的数据。

I tried this, but it doesn't work:

我试过这个,但它不起作用:

request.predicate = NSPredicate(format: "person.self = %@", myPersonObjectID)

1 个解决方案

#1

You should get the object with existingObject from the Object ID and use that in the predicate.

您应该从Object ID获取带有existingObject的对象,并在谓词中使用它。

if let myPerson = context.existingObject(with: myPersonObjectID) {
    request.predicate = NSPredicate(format: "person = %@", myPerson)
}