CODEWITHSUNDEEP
iosswiftrealmnspredicate
cafemike
cafemike

Reputation: 660

Cross-referencing predicate for Realm queries in Swift

So I have been learning Realm in Swift lately and I come across with a design problem regarding a potential notification between data models. It would be greatly appreciated if someone is willing to shed some insight.

// Class A is what users mainly interact with
Class A: Object {
    dynamic var propertyA = ""
    dynamic var propertyB = ""
    dynamic var propertyC = ""

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

// Class B is what the server interacts with, like data feeding
Class B: Object {
    dynamic var propertyA = ""
    dynamic var propertyX = ""
    dynamic var propertyY = ""
    dynamic var propertyZ = ""

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


I have set a notification block for Object A inside the controller. So whenever changes take place in resultObjectsA, the notification block will get triggered.

let resultObjectsA = realm.objects(A).filter('predicate1')
let notificationTokenA = resultObjectsA.addNotificationBlock {
    ...
}


In the app that I am building, the user can select a set of Object A, and the app will query the status of the selection set from the server. The return results will be stored/presented in Object B. Now, I need to write a query/predicate for Object B:

let resultObjectsB = realm.objects(B).filter('predicate2')

such that propertyA in resultObjectB entries can be found in propertyA in resultObjectsA entries, like a one-to-one mapping.

I am not sure if such predicate is doable. If there are other ways to achieve what I would like to do here, I am more than keen to learn as well.

Upvotes: 2

Views: 458

Answers (1)

Dmitry
Dmitry

Reputation: 7350

To query all (actually there should be able one object because of primary key) objects B where objectB.propertyA == objectA.propertyA use:

let resultObjectsB = realm.objects(B).filter('propertyA = %@', objectA.propertyA)

Another option is to use One-to-One relationship between A and B, learn more at https://realm.io/docs/swift/latest/#to-one-relationships

Upvotes: 1

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