Explore Shadow Properties in EF Core

author.cs

public class Author
{
  // omitted properties

  public DateTimeOffset CreatedOn { get; set; }
  public DateTimeOffset? LastUpdatedOn { get; set; }
}

db-context.cs

private void UpdateTrackingDates()
{
    var trackingDatesChangedEntries = this.ChangeTracker.Entries()
        .Where(entry => entry.State == EntityState.Added
                    || entry.State == EntityState.Modified
            && entry.Entity is IHaveTrackingDates
        );

    foreach (var entry in trackingDatesChangedEntries)
    {
        if (entry.State == EntityState.Modified)
            this.Entry(entry).Property("LastUpdatedOn")
                .CurrentValue = DateTimeOffset.UtcNow;
        else if (entry.State == EntityState.Added)
            this.Entry(entry).Property("CreatedOn")
                .CurrentValue = DateTimeOffset.UtcNow;
    }
}

public override int SaveChanges()
{
    this.UpdateTrackingDates();
    return base.SaveChanges();
}

public override Task<int> SaveChangesAsync(
    CancellationToken cancellationToken = new CancellationToken())
{
    this.UpdateTrackingDates();
    return base.SaveChangesAsync(cancellationToken);
}

IHaveTrackingDates.cs

public interface IHaveTrackingDates { }

public class Author : ICanBeSoftDeleted , IHaveTrackingDates
{
 // omitted code
}

on-model-creating.cs

public static void AddTrackingDatesShadowProperties(this ModelBuilder modelBuilder)
{
    var trackingDatesEntities =
                typeof(IHaveTrackingDates)
                .Assembly.GetTypes()
                    .Where(
                        type => typeof(IHaveTrackingDates)
                                    .IsAssignableFrom(type)
                                && type.IsClass
                                && !type.IsAbstract);

    foreach (var entity in trackingDatesEntities)
    {
        modelBuilder.Entity(entity)
            .Property<DateTimeOffset>("CreatedOn")
            .IsRequired();
        modelBuilder.Entity(entity)
            .Property<DateTimeOffset?>("LastUpdatedOn")
            .IsRequired(false)
            .HasColumnName("LastUpdatedAt");
    }
}