Model protocol for Firebase/Database

Model.swift

import Foundation
import FirebaseDatabase

enum ModelError: Error {
    case invalidProperties
}

protocol Model {
    init?(snapshot: FIRDataSnapshot)
    
    var id: String? { get set }
    var serialized: [String : Any] { get }
    
    mutating func store(at ref: FIRDatabaseReference) throws
    func update(at ref: FIRDatabaseReference) throws
    func delete(at ref: FIRDatabaseReference)
    func validate() -> Bool
}

extension Model {
    mutating func store(at ref: FIRDatabaseReference) throws {
        guard validate() else { throw ModelError.invalidProperties }
        
        let child = ref.childByAutoId()
        child.updateChildValues(self.serialized)
        
        self.id = child.key
    }
    
    func update(at ref: FIRDatabaseReference) throws {
        guard validate() else { throw ModelError.invalidProperties }
        
        ref.updateChildValues(self.serialized)
    }
    
    func delete(at ref: FIRDatabaseReference) {
        ref.removeValue()
    }
    
    // MARK: - By default all models are considered valid. Should be overridden.
    func validate() -> Bool {
        return true
    }
}