How to automatically generate fields using Entity Framework when adding and updating records?

I'm having trouble making the "CreatedAt" and "ModifiedAt" fields automatically generated by Entity Framework when adding and updating records in a table. I've tried using the "ValueGeneratedOnAddOrUpdate()" property in my code, but it's not working as expected.

Here's the relevant snippet of my code:

using FazendaEletronica.Domain.Entity;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata.Builders;

namespace FazendaEletronica.Infra.Data.EntitiesConfiguration
{
    public class AnimalConfiguration : IEntityTypeConfiguration<Animal>
    {
        public void Configure(EntityTypeBuilder<Animal> builder)
        {
            builder.HasKey(t => t.Id);
            builder.Property(p => p.Number).IsRequired();
            builder.Property(p => p.SurName).HasMaxLength(100);
            builder.Property(p => p.BirthDay).IsRequired().HasColumnType("Date");
            builder.Property(p => p.CharAnimalSex).HasMaxLength(1).IsRequired();
            builder.Property(p => p.AnimalStatus).IsRequired();
            builder.Property(p => p.Active).IsRequired().HasColumnType("bit");
            builder.Property(p => p.SaleDate).HasColumnType("Date");
            builder.HasOne(a => a.AnimalDad).WithMany(a => a.AnimalsDad).HasForeignKey(a => a.AnimalDadId).IsRequired(false);
            builder.HasOne(p => p.AnimalClass).WithMany(a => a.Animals).HasForeignKey(f => f.AnimalClassId).IsRequired();
            builder.HasOne(p => p.AnimalPurpose).WithMany(a => a.Animals).HasForeignKey(f => f.AnimalPurposeId).IsRequired();
            builder.HasOne(p => p.UserFarm).WithMany(p => p.Animals).HasForeignKey(f => f.UserFarmId).IsRequired();

            builder.Property(p => p.ModifiedAt).ValueGeneratedOnAddOrUpdate();
            builder.Property(p => p.CreatedAt).ValueGeneratedOnAdd();
        }
    }
}

Could someone help me understand why the "ValueGeneratedOnAddOrUpdate()" property is not automatically generating the values? Is there any other approach I can take to achieve this result?

he ValueGeneratedOnAddOrUpdate() method in Entity Framework Core is used to configure a property to have its value automatically generated when a new record is inserted or updated. However, the behavior you are experiencing might be due to the fact that ValueGeneratedOnAddOrUpdate() is not supported for all property types.

One option is to handle it in the DataContext.OnSaveChanges using a base class to identify which entities you want to automatically handle:

public abstract class EditableEntityBase
{
    [DateTimeKind(DateTimeKind.Local), DatabaseGenerated(DatabaseGeneratedOption.Computed)]
    public DateTime CreatedAt { get; set; }
    [DateTimeKind(DateTimeKind.Local), DatabaseGenerated(DatabaseGeneratedOption.Computed)]
    public DateTime LastModAt { get; set; }
}

/// <summary>
/// Implementation override for saving changes. This ensures that CreatedBy/At
/// and ModifiedBy/At are recorded.
/// </summary>
public override int SaveChanges()
{
    // Optional if you want a soft-delete system (I.e. IsActive=false rather than Delete...
    // These DbContexts do not allow for hard Deletes. 
    if (ChangeTracker.Entries().Any(x => x.State == EntityState.Deleted
            && typeof(EditableEntityBase).IsAssignableFrom(x.GetType())))
        throw new ApplicationException("Hard deletes are not supported.");

    var updatedEntities = ChangeTracker.Entries()
        .Where(x => x.State == EntityState.Modified)
        .Select(x => x.Entity)
        .Cast<EditableEntityBase>();
    foreach (var entity in updatedEntities)
    {
        entity.LastModAt = DateTime.Now;
    }

    var insertedEntities = ChangeTracker.Entries()
        .Where(x => x.State == EntityState.Added)
        .Select(x => x.Entity)
        .Cast<EditableEntityBase>();
    foreach (var entity in insertedEntities)
    {
        entity.CreatedAt = entity.LastModAt = DateTime.Now;
    }

    return base.SaveChanges();
}