How To Save Only One Instance Of Class In Realm - swift

Question

So instead of using user defualts I want to persist some settings using Realm.
I've created a class for the settings
import Foundation
import RealmSwift
class NutritionSettings: Object {
#objc dynamic var calories: Int = 0
#objc dynamic var proteins: Int = 0
#objc dynamic var carbohydrates: Int = 0
#objc dynamic var fats: Int = 0
}
But in my view controller I don't know how to save just one instance of it
I've tried
let realm = try! Realm()
let settings = NutritionSettings()
do {
try realm.write{
settings.calories = cals!
settings.carbohydrates = carbs!
settings.fats = fats!
settings.proteins = proteins!
}
} catch {
print("error saving settings")
}
Since I know doing realm.add would just add another NutritionSettings object which is not what I want. I was unable to clarify anything using the documentation. Any help would be appreciated thanks.

Answer 1

I faced a similar issue in my project when I tried to save a user session object. If you want to save a unique object, override the primaryKey() class method and set the unique key for it.
#objcMembers class NutritionSettings: Object {
static let uniqueKey: String = "NutritionSettings"
dynamic var uniqueKey: String = NutritionSettings.uniqueKey
dynamic var calories: Int = 0
override class func primaryKey() -> String? {
return "uniqueKey"
}
}
Then to receive the object just use the unique key.
// Saving
let settings = NutritionSettings()
settings.calories = 100
do {
let realm = try Realm()
try realm.write {
realm.add(settings, update: .modified)
}
} catch {
// Error handling
}
// Reading
var settings: NutritionSettings?
do {
let realm = try Realm()
let key = NutritionSettings.uniqueKey
settings = realm.object(ofType: NutritionSettings.self, forPrimaryKey: key)
} catch {
// Error handling
}
if let settings = settings {
// Do stuff
}
Hope it will help somebody.

Answer 2

If you look at the example realm provides https://realm.io/docs/swift/latest you can see that in order to only save one object you still have to do an add. Once you have added the object to the database you can fetch that object and do a write that modifies the internal properties
let realm = try! Realm()
let settings = NutritionSettings()
settings.id = 1
do {
try realm.write{
realm.add(settings)
}
} catch {
print("error saving settings")
}
Next you can fetch and modify that single instance that you saved
let realm = try! Realm()
let settings = realm.objects(NutritionSettings.self).filter("id == 1").first
do {
try realm.write{
settings.calories = cals!
settings.carbohydrates = carbs!
settings.fats = fats!
settings.proteins = proteins!
}
} catch {
print("error saving settings")
}