public DbController(PawnShopDbContext db, UserManager <User> userManager, RoleManager <Role> roleManager, DatabaseMigrator migrator) { _roleManager = roleManager; _db = db.GuardIsNotNull(nameof(db)); _userManager = userManager.GuardIsNotNull(nameof(userManager)); _roleManager = roleManager.GuardIsNotNull(nameof(roleManager)); _migrator = migrator.GuardIsNotNull(nameof(migrator)); }