Entity Framework 6 (code first) entity versioning and auditing

By overloading the dbContext SaveChanges() method, I used the second strategy you mention:

public class MyContext : DbContext
{

 public int SaveChanges(int userId)
 {
    // Get all Added/Deleted/Modified entities (not Unmodified or Detached)
    foreach (var ent in this.ChangeTracker.Entries().Where(p => p.State ==  EntityState.Added 
    || p.State == EntityState.Deleted || p.State == EntityState.Modified))
    {

        foreach (AuditLog x in GetAuditRecordsForChange(ent, userId))
        {
            this.AuditLogs.Add(x);
        }
    }
    return base.SaveChanges();
  }
...

So, to log a specific item, I just call the overloaded SaveChanges function and supply a UserId:

public void Update(StockCatalogueItem entity, int userId)
{
     _context.SaveChanges(userId);
}

I also follow a tradition.DoNotLog I decorate the entity properties I don't want to log with an attribute. Without this, since each entity alteration results in one database entry, the logging might produce a significant volume of data.

[DoNotLog]
public int CreatedBy { get; set; }

The GetAuditRecordsForChange method checks to see whether there are anyDoNotLog features and produces aList<AuditLog> which is recorded and stored in the AuditLogs table:

public class AuditLog
    {
        public int Id { get; set; }
        public int CreatedBy { get; set; }
        public DateTime CreatedOn { get; set; }
        public AuditEventType EventType { get; set; }
        public string TableName { get; set; }
        public int EntityId { get; set; }
        public string ColumnName { get; set; }
        public string Controller { get; set; }
        public string Action { get; set; }
        public string IPAddress { get; set; }
        public string OriginalValue { get; set; }
        public string NewValue { get; set; }
    }