Value generators don't work owned entity's properties

[salaros]

Value generators don't work owned entity's properties

Steps to reproduce

public class Person 
{
	public string Name { get; set; }

	public AuditLog AuditLog { get; set; }
}

[Owned]
public class AuditLog : IHasSoftDelete
{
    public bool IsDeleted { get; set; }

    public DateTime CreatedTime { get; set; }

    public DateTime? ModifiedTime { get; set; }

    public string CreatedBy { get; set; }

    public string ModifiedBy { get; set; }
}

public class CurrentUserNameGenerator : ValueGenerator<string>
{
    public override bool GeneratesTemporaryValues => false;

    public override string Next(EntityEntry entry) => "FooBarUser";
}

dbContext
    .Entity<Person>()
    .OwnsOne(p => p.AuditLog)
    .Property(a => a.CreatedBy)
    .HasColumnName(nameof(AuditLog.CreatedBy))
    .HasValueGenerator<CurrentUserNameGenerator>() // <-- the generator is not triggered when CreatedBy is null
    .IsRequired(true); // doesn't work BTW, it's just ignored

Further technical details

EF Core version: 3.0.0
Database provider: Microsoft.EntityFrameworkCore.SqlServer
Target framework: NET Core 3.0
Operating system: Windows 10 1903 Pro x64 EN
IDE: Visual Studio 2019 16.3.x

[ajcvickers]

Note for triage: Calling HasValueGenerator does not make the property ValueGenerated.OnAdd.

@salaros Explicitly specify that the property should get a generated value when a new entity is being attached:

modelBuilder.Entity<Person>()
    .OwnsOne(p => p.AuditLog)
    .Property(a => a.CreatedBy)
    .HasColumnName(nameof(AuditLog.CreatedBy))
    .ValueGeneratedOnAdd()
    .HasValueGenerator<CurrentUserNameGenerator>()
    .IsRequired(true);