How to set the latest date modified after saving changes

Question

I have an interface for some of my DB models:

    public interface IBaseEntity<T> where T: struct
    {
        public T Id { get; set; }
        public DateTime LastUpdated { get; set; }
    }

And I want automatic set property LastUpdated to DateTime.Now after saving entity. This is my override of ef SaveChanges method:

        public override int SaveChanges()
        {
            var entries = ChangeTracker
                .Entries()
                .Where(e => e.Entity is IBaseEntity<???>  
                                 /* How I can check this condition? 
                                  What I should pass in a generic? 
                                  It can be any struct (Guid or int for example).
                                 */ 
                       && (
                        e.State == EntityState.Added
                        || e.State == EntityState.Modified));

            foreach (var entityEntry in entries)
            {
                ((IBaseEntity<???>)entityEntry.Entity).LastUpdated = DateTime.Now;
            }
...

Is it possible to use my interface 'IBaseEntity where T: struct' in such solution?

I don't know what I should pass in generic type, my Id can be a Guid or Int, but I can't do like this:
IBaseEntity<struct>, IBaseEntity<object>, IBaseEntity<ValueType>, IBaseEntity<int | Guid> // this is all invalid

Answer 1

You can extract non generic interface with LastUpdated property as a root of hierarchy and inherit IBaseEntity from it. Then you can work with this non generic interface in SaveChanges() implementation.

public interface IBaseEntity
{
    DateTime LastUpdated { get; set; }
}

public interface IBaseEntity<T> : IBaseEntity where T : struct
{
    T Id { get; set; }
}

Answer 2

I use an abstract BaseEntity class instead of an interface. BaseEntity contains the UpdatedDateTime attribute. Some of my entities inherit from this abstract class. In the context event handler I use the condition entityEntry.Entity is BaseEntity, without having to know the type of the actual entity.