Soft-deletable entities

wat.cs

	interface ISoftDeletable {
		DateTime? Deleted { get; set; }
	}

	class MyEntity : ISoftDeletable {
		public Int64 Id { get; set; }
		public String Name { get; set; }
		public DateTime? Deleted { get; set; }
	}

	class MyDbContext : DbContext {
		public DbSet<MyEntity> MyEntities { get; set; }

		private void ProcessDeletes() {
			var softDeletableEntries = ChangeTracker.Entries<ISoftDeletable>();
			foreach (var sde in softDeletableEntries) {
				if (sde.State == EntityState.Deleted && sde.Entity.Deleted == null) {
					sde.Entity.Deleted = DateTime.UtcNow;
					sde.State = EntityState.Modified; // Prevent the hard delete, but allow the modified `Deleted` field to be persisted
				}
			}
		}

		public override Int32 SaveChanges() {
			ProcessDeletes();
			return base.SaveChanges();
		}

		public override Task<Int32> SaveChangesAsync(CancellationToken cancellationToken) {
			ProcessDeletes();
			return base.SaveChangesAsync(cancellationToken);
		}
	}