Get current user id in dbcontext - entity-framework

Question

I am working on an ASP.NET Core web application. This application works with a SQL Server database and I am using Entity Framework 6.
I want to automatically add, on each entity, a last modification date and user id.
My question is: how can I automatically set the user id to each entity?
I have tried to override SaveChanges() in the DbContext. It works fine, but I can't access the Microsoft identity classes there...
Thanks

Answer 1

(Apologies in advance if the method signatures look a bit odd, I'm one of the rare breed that uses explicit interface implementation to help avoid stale code dust-bunnies littering code as I re-factor)
An example on accessing a session state to get the user from within a DbContext using a session token from a Forms Authentication web application:
[Serializable]
public class UserDetails
{
public int UserId { get; set; }
public string DisplayName { get; set; }
}
public interface ISessionHelper
{
UserDetails CurrentUser { get; set; }
void Clear();
bool IsAuthenticated();
}
public class SessionHelper : ISessionHelper
{
private const string UserDetailsKey = "YourUniqueSessionIdKey";
private ISessionHelper This => this;
UserDetails ISessionHelper.CurrentUser
{
get
{
try
{
var token = (UserDetails)HttpContext.Current.Session[UserDetailsKey];
return token;
}
catch
{
throw new ApplicationException("The current session could not be resolved.");
}
}
set
{
try
{
HttpContext.Current.Session[UserDetailsKey] = value;
}
catch
{
throw new ApplicationException("The current session state could not be set.");
}
}
}
/// <summary>
/// <see cref="ISessionHelper.Clear"/>
/// </summary>
void ISessionHelper.Clear()
{
HttpContext.Current.Session.Clear();
}
/// <summary>
/// <see cref="ISessionHelper.IsAuthenticated(string)"/>
/// </summary>
bool ISessionHelper.IsAuthenticated()
{
try
{
var cookie = HttpContext.Current.Request.Cookies[FormsAuthentication.FormsCookieName];
var ticket = FormsAuthentication.Decrypt(cookie.Value);
var userDetails = This.CurrentUser;
return (userDetails != null && userDetails.UserId != 0);
}
catch
{
return false;
}
}
}
public interface ICurrentUserLocator
{
bool IsUserLoggedIn { get; }
int CurrentUserId { get; }
string CurrentUserDisplayName { get; }
}
public sealed class FormsAuthenticationUserLocator : ICurrentUserLocator
{
private const string UnauthorizedAccessExceptionMessage = "No user is currently logged in.";
private readonly ISessionHelper _sessionHelper = null;
[ExcludeFromCodeCoverage]
private ICurrentUserLocator This => this;
private UserDetails _userDetails = null;
[ExcludeFromCodeCoverage]
private UserDetails CurrentUser
{
get { return _userDetails ?? (_userDetails = SessionHelper.UserDetails); }
}
[ExcludeFromCodeCoverage]
bool ICurrentUserLocator.IsUserLoggedIn => CurrentUser != null;
[ExcludeFromCodeCoverage]
int ICurrentUserLocator.CurrentUserId => CurrentUser?.UserId ?? throw new UnauthorizedAccessException(UnauthorizedAccessExceptionMessage);
[ExcludeFromCodeCoverage]
string ICurrentUserLocator.CurrentUserDisplayName => CurrentUser?.DisplayName ?? throw new UnauthorizedAccessException(UnauthorizedAccessExceptionMessage);
public FormsAuthenticationUserLocator(ISessionHelper sessionHelper)
{
_sessionHelper = sessionHelper ?? throw new ArgumentNullException("sessioNHelper");
}
}
Assuming you are using dependency injection with a container, register the two classes against their respective interfaces in the container on a per-request lifespan. Then add a dependency on ICurrentUserLocator into your DbContext:
public class AppDbContext : DbContext
{
private readonly ICurrentUserLocator _currentUserLocator = null;
public AppDbContext(ICurrentUserLocator currentUserLocator)
{
_currentUserLocator = currentUserLocator ?? throw new ArgumentNullException("currentUserLocator");
}
}
Now in your overridden SaveChanges you can fetch the current user ID:
var currentUser = Users.Single(x => x.UserId == _currentUserLocator.CurrentUserId);
var updatedEntities = ChangeTracker.Entries()
.Where(x => x.State == EntityState.Modified)
.Select(x => x.Entity)
.Cast<EditableEntityBase>();
foreach (var entity in updatedEntities)
{
entity.LastModifiedBy = currentUser;
entity.LastModifiedAt = DateTime.Now;
}
var insertedEntities = ChangeTracker.Entries()
.Where(x => x.State == EntityState.Added)
.Select(x => x.Entity)
.Cast<EditableEntityBase>();
foreach (var entity in insertedEntities)
{
entity.CreatedBy = entity.LastModifiedBy = currentUser;
entity.CreatedAt = entity.LastModifiedAt = DateTime.Now;
}
If you only expose the FKs rather than user navigation properties then you can just set the ID. If your app has a Log Out feature be sure to call the SessionHelper.Clear() method. In this example I modified the session helper I typically use to just focus on the current user details to keep it simple. It normally tracks a few other details, hence why the Clear() method wipes the entire session. It's a standardized wrapper for handling known session state rather than littering code with Session["somestring"] everywhere.