Update user and roles in single Db Call using MVC 5 Identity

Question

I'm new to Asp.net Identity. I'm trying to write a method which will update user details and its role. How can I achieve this by making single call to database.

var userStore = new UserStore<ApplicationUser>(DbContext);
 _userManager = new UserManager<ApplicationUser>(userStore);

Adding roles

_userManager.AddToRole(userId, role);

updating user

_userManager.Update(user);

Is there a way to call context.savechanges on usermanager so that I can make sure both action takes place or none?