Persister is a protocol that holds all the queries logic

Persister.swift

protocol Persister {
    static func select<T: CodableObject>(type: T.Type, filter: NSPredicate?) -> Results<T>
    static func insert(object: CodableObject, update: Bool?)
    static func insert(objects: [CodableObject], update: Bool?)
    static func delete(object: CodableObject)
    static func delete<T: CodableObject>(type: T.Type, filter: NSPredicate?)
    static func deleteAll<T: CodableObject>(type: T.Type)
    static func resetDB()
}