Compound Key in Realm with Lazy Property

Compound key in Realm with lazy property

The solution you found is outdated. I'll leave a note about that there. I'd suggest removing the lazy modifier and initializing compoundKey to an empty string.

Realm Swift Composite Keys for Optional Properties

You need to set RealmOptional's value member. RealmOptional properties cannot be var because Realm can't detect assignment to property types that cannot be represented by the Objective-C runtime, which is why RealmOptional, List and LinkingObjects properties must all be let.

class Item: Object {
    dynamic var id = 0
    let importantNumber = RealmOptional<Int>()
    let importantNumber2 = RealmOptional<Int>()

    func setCompoundID(id: Int) {
        self.id = id
        compoundKey = compoundKeyValue()
    }

    func setCompoundImportantNumber(importantNumber: Int) {
        self.importantNumber.value = importantNumber
        compoundKey = compoundKeyValue()
    }

    func setCompoundImportantNumber2(importantNumber2: Int) {
        self.importantNumber2.value = importantNumber2
        compoundKey = compoundKeyValue()
    }

    dynamic lazy var compoundKey: String = self.compoundKeyValue()

    override static func primaryKey() -> String? {
        return "compoundKey"
    }

    func compoundKeyValue() -> String {
        return "\(id)\(importantNumber)\(importantNumber2)"
    }
}

Realm.io and compound primary keys

It appears that is the correct way to return a compound key in Realm.

Here's the answer from Realm : https://github.com/realm/realm-cocoa/issues/1192

You could use a mix of lazy and didSet instead to have the compoundKey
property be both derived and stored:

public final class Card: Object {
    public dynamic var id = 0 {
        didSet {
            compoundKey = compoundKeyValue()
        }
    }
    public dynamic var type = "" {
        didSet {
            compoundKey = compoundKeyValue()
        }
    }
    public dynamic lazy var compoundKey: String = self.compoundKeyValue()
    public override static func primaryKey() -> String? {
        return "compoundKey"
    }

    private func compoundKeyValue() -> String {
        return "\(id)-\(type)"
    }
}

// Example

let card = Card()
card.id = 42
card.type = "yolo"
card.compoundKey // => "42-yolo"

composite primary key realm/swift

For 1.0.1+ of Realm:

class DbLocation: Object{
    dynamic var id = 0
    dynamic var tourId = 0
    dynamic var compoundKey = ""

    override static func primaryKey() -> String? {
        return "compoundKey"
    }

    func setup(id: Int, tourId: Int){
        self.id = id
        self.tourId = tourId
        self.compoundKey = compoundKeyValue()
    }

    func compoundKeyValue() -> String {
        return "\(id)\(tourId)"
    }
}

Usage example:

let location = DbLocation()
location.setup(id: 0, tourId: 1) 
print(location.compoundKey) // "01"

Of course you can play around with using various didSet listeners on id and tourId, to make sure that compoundKey gets properly rewritten every time the values get changed.

For pre-1.0.1 of Realm:

class DbLocation: Object {
    dynamic var id = 0
    dynamic var tourId = 0

    func setCompoundID(id: Int) {
        self.id = id
        compoundKey = compoundKeyValue()
    }

    func setCompoundTourId(tourId: Int) {
        self.tourId = tourId
        compoundKey = compoundKeyValue()
    }

    dynamic lazy var compoundKey: String = self.compoundKeyValue()

    override static func primaryKey() -> String? {
        return "compoundKey"
    }

    func compoundKeyValue() -> String {
        return "\(id)\(tourId)"
    }
}

The custom setters make sure, that the compoundKey is always updated, the lazy key word makes sure that the first time you access it, it will be derived from what you've already set.

Find out more on this topic in this thread where this issue has been debated.

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