@Observable class CoreDataInterViewModel{
let container: NSPersistentContainer
var savedEntities: [Fish] = []

init() {
    container = NSPersistentContainer(name: "Fish")
    container.loadPersistentStores { (desciption, error) in
        if let error = error {
            print("ERROR LOADING CORE DATA. \(error)")
        } else {
            print("SUCCESSFULLY LOADED CORE DATA. \(desciption)")
        }
    }
    fetchFish()
}

// MARK: - FUNCTION

 func fetchFish() {
    
    let request = NSFetchRequest<Fish>(entityName: "Fish")
    do {
        savedEntities = try container.viewContext.fetch(request)
    } catch  {
        print("ERROR FETCHING CORE DATA: \(error)")
    }
}

 func saveData() {
    do {
        try container.viewContext.save()
        fetchFish()
        
    } catch {
        print("Error SAVING: \(error)")
    }
}

ViewModel code