EntityFramework Core 2 - ValueGeneratedOnAddOrUpdate [duplicate]

Question

I have a scenario where my model has the fields CreatedOn and UpdatedOn and following what I found in the documentation of EF Core I implemented my class as follows

builder.Entity<Registro>(b =>
    {
        b.Property<DateTime>("CreatedOn")
            .IsRequired()
            .ValueGeneratedOnAdd()
            .HasDefaultValueSql("GETUTCDATE()");

        b.Property<DateTime>("UpdatedOn")
            .IsRequired()
            .ValueGeneratedOnAddOrUpdate()
            .HasDefaultValueSql("GETUTCDATE()"); ;
    });

public class Registro
{
    public Guid Id { get; set; }
    public string Nome { get; set; }
}

On insert both fields are saved with the correct value, however the update it does not happen as I expected, the UpdatedOn keeps the save value. It also follows how I am doing the entity update

public void Put(Guid id, [FromBody]string value)
{
    var r = context.Registros.SingleOrDefault(x => x.Id == id);

    r.Nome = value;

    context.SaveChanges();
}

Answer 1

To get your UpdatedOn timestamp to update automatically, one method you could choose is to implement an interface describing the functionality and overload the DbContexts SaveChanges method.

public interface IUpdateable 
{ 
    DateTime UpdatedOn { get; set; }  
}

public class Registro : IUpdateable
{
    public Guid Id { get; set; }
    public string Nome { get; set; }
    public DateTime UpdatedOn { get; set; }
}

And then within your Context class

public override int SaveChanges()
{
    var currentDateTime = DateTime.Now;
    var entries = ChangeTracker.Entries().ToList();

    // get a list of all Modified entries which implement the IUpdatable interface
    var updatedEntries = entries.Where(e => e.Entity is IUpdateable)
            .Where(e => e.State == EntityState.Modified)
            .ToList();

    updatedEntries.ForEach(e =>
    {
        ((IUpdateable)e.Entity).UpdatedOn = currentDateTime;
    });


    return base.SaveChanges();
}