using ThreadSafeReference can only get dynamic value - ios

Question

I have a Store, Area table, After called api get the Store Area data, then will create Store , Area table;
Goal: For render ui, i need Store with areaName. fetch stores from db and then compose to stores with areaName, then compose to a 2d array based on areaName in background thread. then pass the 2d array to render ui in main thread
Implementation:
In the background thread read Store, using areaCode get Area, then get areaName, then store.areaName = area.areaName get the composed Store, and using ThreadSafeReference to get the reference of store
In the main thread using realm.resolve to get the store in main thread, but can only get the store.address value, can not get the store.areaName
class Store: Object {
dynamic var storeCode: String = ""
dynamic var areaCode: String = ""
dynamic var address: String = ""
dynamic var phone: String = ""
var areaName: String = ""
var userId: Int = 0
}
class Area: Object {
dynamic var areaCode: String = ""
dynamic var areaName: String = ""
}
//// in background thread//////
let realmInBack = try! Realm()
let stores = getStore(by userId: Int) // here get a list of stores from db
stores.forEach{ (store) in
let area = getArea(by areaCode: String) // get area
let areaName = area.areaName // get the areaName from area
store.areaName = areaName // assign areaName to store
let storeRef = ThreadSafeReference(to: store) // get the storeRef
}
//// in main thread /////
let realm = try! Realm()
let storeInMain = realm.resolve(storeRef)
// then use storeInMain to render ui
Could please list the ways to pass realm object through threads?
I currently know the following ways:
1. ThreadSafeReference(failed in my case)
2. transform the realm object to normal class by myself

Answer 1

For this simple case, you don't actually need to use a ThreadSafeReference object. You should just save a property of your object to a variable you can use to identify that specific object (preferably its primaryKey if you are using primaryKeys), then retrieve the object using its primary key from Realm on the main thread.
var storeCodeRef = "" //make sure this variable is accessible in the scope of where your code on the main thread is called from as well
let realmInBack = try! Realm()
let stores = getStore(by userId: Int) // here get a list of stores from db
stores.forEach{ (store) in
let area = getArea(by areaCode: String) // get area
let areaName = area.areaName // get the areaName from area
store.areaName = areaName // assign areaName to store
//save the unique identifier for the store
storeCodeRef = store.storeCode
}
//// in main thread /////
let realm = try! Realm()
let store = realm.object(ofType: Store.self).filter("storeCode == %#",storeCodeRef).first //assuming storeCodes are unique
If you are using a primary key, you can use
let store = realm.object(ofType: Store.self, forPrimaryKey: storeCodeRef)
Since you declare a new reference to your Realm instance on the main thread and access the Store object from that reference, you won't receive any errors.
Update based on comments:
Your Class model is flawed. All properties that you want to persist in Realm need to be declared using the dynamic keyword, otherwise they cannot be dynamically dispatched to the Obj-C runtime, which Realm uses.
class Store: Object {
dynamic var storeCode: String = ""
dynamic var areaCode: String = ""
dynamic var address: String = ""
dynamic var phone: String = ""
dynamic var areaName: String = ""
dynamic var userId: Int = 0
}
Second of all, why do you store ThreadSafeReferences to individual stores if you want to modify the actual Store objects, you can do that in a write transaction and store a ThreadSafeReference to the Results instance, so you only need to resolve a single reference and not one for each individual Store.
Below code has been tested and is working in a Realm playground.
class Store: Object {
dynamic var storeCode: String = ""
dynamic var address: String = ""
dynamic var phone: String = ""
dynamic var userId: Int = 0
dynamic var areaCode: String = ""
dynamic var areaName: String = ""
}
class Area: Object {
dynamic var areaCode: String = ""
dynamic var areaName: String = ""
}
try! realm.write {
realm.add([Store(value: ["userId":1,"storeCode":"1"]),Store(value: ["userId":1,"storeCode":"2"]),Store(value: ["userId":2,"storeCode":"1"])])
}
print(realm.objects(Store.self))
//// in some thread//////
var storesRef: ThreadSafeReference<Results<Store>>?
DispatchQueue(label: "background").sync {
autoreleasepool{
let realmInBack = try! Realm(configuration: Realm.Configuration(inMemoryIdentifier: "TemporaryRealm"))
let stores = realmInBack.objects(Store.self).filter("userId == 1")
print("Stores for user 1:",stores)
try! realmInBack.write {
let area = Area(value: ["areaCode":"a","areaName":"AreaA"])
realmInBack.add(area)
stores.forEach{ (store) in
store.areaCode = area.areaCode
}
}
print("Modified stores:",stores)
storesRef = ThreadSafeReference(to: stores)
}
}
//// in main thread /////
DispatchQueue.main.async {
let mainRealm = try! Realm(configuration: Realm.Configuration(inMemoryIdentifier: "TemporaryRealm"))
guard let storesRef = storesRef, let storeInMain = mainRealm.resolve(storesRef) else {
print("Couldn't resolve stores reference"); return
}
print("Stores from ThreadSafeReference:",storeInMain)
}