PlanetManager.swift

func tryStoringDefaultPlanets() {
    // dataStore is an instance of NSPersistentContainer subclass CoreDataStore.
    guard dataStore.count(for: "Planet") == 0 else { return }
    
    // Insert new entities into managed object context.
    let names = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
    let paths = ["https://en.wikipedia.org/wiki/Mercury_(planet)", "https://en.wikipedia.org/wiki/Venus", "https://en.wikipedia.org/wiki/Earth", "https://en.wikipedia.org/wiki/Mars", "https://en.wikipedia.org/wiki/Jupiter", "https://en.wikipedia.org/wiki/Saturn", "https://en.wikipedia.org/wiki/Uranus", "https://en.wikipedia.org/wiki/Neptune"]
    zip(names, paths).enumerated().forEach { (offset, element) in
        guard let planet = dataStore.insertNewEntity(named: "Planet") as? Planet else { return }
        planet.position = Int64(offset)
        planet.name = element.0
        planet.url = URL(string: element.1)
    }
    // Save changes in the managed object context what at the moment contains added Planets.
    dataStore.save()
}