Correct way of creating reference to object in Realm - ios

Question

I create a fitness app and I use Realm as local database. During first launch I want to replace default realm with realm file which contains initial data (names of exercises, equipment, muscles engaged etc.). This initial data won't change in future. I wonder if exists some way which can help me to create reference in main class to another smaller classes. I need this to make filtering and getting data easier.
It's my main realm class
class Exercise: Object {
#Persisted var exerciseID: Int = 0
#Persisted var name: String = ""
#Persisted var category: Int
#Persisted var equipment: String
#Persisted var instruction: String
#Persisted var muscle: String
#Persisted var gif: String?
#Persisted var image: String? = nil
convenience init(name: String, category: Int, equipment: String, instruction: String, muscle: String, gif: String?, image: String?) {
self.init()
self.name = name
self.category = category
self.equipment = equipment
self.instruction = instruction
self.muscle = muscle
self.gif = gif
self.image = image
}
override static func primaryKey() -> String? {
return "exerciseID"
}
}
When I want to get all exercises and assigned equipment and muscles it is really a lot of code to retrieve this data especially when string contains few references to object.
var exercises = [Exercise]()
var equipments = [Equipment]()
func getAllExercises() {
let data = RealmService.shared.realm.objects(Exercise.self)
exercises = data.compactMap({$0})
let equipment = exercises.compactMap({$0.equipment})
for eq in exercises.compactMap({$0.equipment}) {
let numberOfEquipment = eq.components(separatedBy: ",")
for number in numberOfEquipment {
guard let intNumber = Int(number) else { return }
guard let finalEquipment = RealmService.shared.realm.object(ofType: Equipment.self, forPrimaryKey: intNumber) else { return }
equipments.append(finalEquipment)
}
}
Maybe the better option is to just insert values instead of object references?

Answer 1

You need to set up one-to-many relationships to take advantage of quicker queries and lazy loading.
I've simplified the models, but the magic is in the equipmentObjects property:
class Exercise: Object {
#Persisted(primaryKey: true) var exerciseID = 0
#Persisted var name: String = ""
#Persisted var equipment: String
#Persisted var equipmentObjects: List<Equipment>
convenience init(exerciseID: Int, name: String, equipment: String) {
self.init()
self.exerciseID = exerciseID
self.name = name
self.equipment = equipment
}
}
class Equipment: Object {
#Persisted(primaryKey: true) var equipmentID = 0
#Persisted var equipment: String = ""
convenience init(equipmentID: Int, equipment: String) {
self.init()
self.equipmentID = equipmentID
self.equipment = equipment
}
}
You can go ahead and initialize realm with your csv file. But when the app begins you would want to go ahead and establish the relationships between Exercise, Equipment, and Muscles. You should only do this once.
Here I've created a small utility to link the realm objects. Notice how it uses UserDefaults to check and see if relationships were already built. It is also building the relationships on a specified queue. You would want to pass in a background queue rather than the main queue so the UI doesn't lock up.
struct RealmRelationshipBuilder {
let configuration: Realm.Configuration
let userDefaults: UserDefaults
let queue: DispatchQueue
func buildRelationshipsIfNeeded(completion: #escaping() -> Void) {
guard userDefaults.didBuildRealmRelationships == false else { return completion() }
queue.async {
autoreleasepool {
defer { completion() }
do {
let realm = try Realm(configuration: configuration)
try realm.write {
realm.objects(Exercise.self).forEach { exercise in
let equipment = exercise
.equipment
.components(separatedBy: ",")
.compactMap(Int.init)
.compactMap { realm.object(ofType: Equipment.self, forPrimaryKey: $0) }
exercise.equipmentObjects.append(objectsIn: equipment)
}
}
} catch {
print("RealmRelationshipBuilder error: \(error)")
}
userDefaults.didBuildRealmRelationships = true
}
}
}
}
extension UserDefaults {
enum Key {
static let didBuildRealmRelationships = "didBuildRealmRelationshipsKey"
}
var didBuildRealmRelationships: Bool {
get { bool(forKey: Key.didBuildRealmRelationships) }
set { set(newValue, forKey: Key.didBuildRealmRelationships) }
}
}
Then to test the builder here is a small test case. But in reality you would probably want to show the user an status indicator while the relationships are being built in the background.
enum InitialData {
static let exercises: [Exercise] = {
[
Exercise(exerciseID: 1, name: "Bench press", equipment: "1,3,5"),
Exercise(exerciseID: 2, name: "Butterfly", equipment: "6"),
]
}()
static let equipment: [Equipment] = {
[
Equipment(equipmentID: 1, equipment: "Barbell"),
Equipment(equipmentID: 2, equipment: "Bench"),
Equipment(equipmentID: 3, equipment: "Bodyweight"),
Equipment(equipmentID: 4, equipment: "Cable"),
Equipment(equipmentID: 5, equipment: "Not sure"),
Equipment(equipmentID: 6, equipment: "Unknown"),
]
}()
}
class RealmExerciseTests: XCTestCase {
let realmConfiguration = Realm.Configuration.defaultConfiguration
override func setUpWithError() throws {
let realm = try Realm(configuration: realmConfiguration)
try realm.write {
realm.deleteAll()
realm.add(InitialData.exercises)
realm.add(InitialData.equipment)
}
}
func testInitialize() throws {
let relationshipBuilder = RealmRelationshipBuilder(
configuration: realmConfiguration,
userDefaults: .init(suiteName: UUID().uuidString) ?? .standard,
queue: DispatchQueue(label: "realm.init.background")
)
let expectation = expectation(description: "realm.init")
relationshipBuilder.buildRelationshipsIfNeeded {
expectation.fulfill()
}
wait(for: [expectation], timeout: 2.0)
let realm = try Realm(configuration: realmConfiguration)
realm.refresh()
guard let exercise1 = realm.object(ofType: Exercise.self, forPrimaryKey: 1) else {
return XCTFail("Missing exercise with primary key 1")
}
guard let exercise2 = realm.object(ofType: Exercise.self, forPrimaryKey: 2) else {
return XCTFail("Missing exercise with primary key 2")
}
XCTAssertEqual(exercise1.equipmentObjects.count, 3)
XCTAssertEqual(exercise2.equipmentObjects.count, 1)
}
}