领域关系在不应该返回时返回nil

Question

class Book: Object {
    // (…)
    var readingSessions: [ReadingSession] {
        return linkingObjects(ReadingSession.self, forProperty: "book")
    }
}

class ReadingSession: Object {
    // (…)
    var book: Book?

    var aComputedProperty: Int {
        print(self) // Prints ReadingSession { book = Book { (…) } (…) }
        print(self.book) // Prints nil
        // (…)
    }
}

The code pretty much says it all. If I print self from within my computed property it prints the related object among the other properties like I expect. If I just try to get that object, though, it returns nil . Is that supposed to happen? Am I doing something wrong?

Thanks in advance,

Daniel

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Edit: It seems the problem isn't actually related to computed properties. Just calling this from a regular view controller gives me the same problem:

let session = ReadingSession()
// (…)
print(session) // This returns every property, including the Book
print(session.book) // This returns nil

It doesn't happen always, though. On some parts of my code I do the same thing and it works as expected, in other parts this happens. So I guess I'm just making some silly mistake somewhere, but I have no idea what could be causing this.

---

let realm = try! Realm()

let sessions = realm.objects(ReadingSession).filter("book = %@", user.selectedBook!).sorted("date")
let session = sessions[indexPath.row]
print(session.book) // prints nil
session.book = user.selectedBook!
print(session.book) // prints the correct book

I don't understand! I'm filtering the sessions based on a Book . When I print the filtered session's book shouldn't it return the book I used to filter it? But it only works if I set its book property to that same book again!

Answer 1

You have to declare the user property as dynamic var to make this work:

class ReadingSession: Object {
    dynamic var book: Book?
    //...
}