An example of a custom save call for an automatic updated_at field.

CustomSaveStruct.swift

import Vapor
import Fluent
import Foundation

struct User: Model {
    var updated_at: Int
    
    //...
    
    mutating func save() throws {
        updated_at = Int(Date().timeIntervalSince1970)
        try User.query().save(&self)
    }
}