Temporal table usage

[jovball]

I would like to use a Facet DTO with temporal tables. How would you recommend doing that? IMO, it would be nice if Facet would generate the temporal properties (ValidTo/ValidFrom) based on the EF ModelBuilder configuration having IsTemporal defined.

    config.ToTable("MyTable", "dbo", b=>b.IsTemporal(b=> { b.HasPeriodStart("ValidFrom"); b.HasPeriodEnd("ValidTo");})); 

Then it would populate them when I call SelectFacet.

[Tim-Maes]

Hi @jovball

The easiest way to use Facet with temporal tables today is to make ValidFrom/ValidTo real properties on your entity instead of shadow properties. Facet will then pick them up automatically — no changes needed.

EF Core temporal period columns (ValidFrom/ValidTo) are typically configured as shadow properties .. they exist in the database but not as C# properties on the entity class.

Facet is a compile-time source generator that analyzes the entity type via Roslyn. Since shadow properties don't exist on the type definition, and OnModelCreating configuration is a runtime thingy, the generator justcan't see them.

What works today:

Make the period columns real properties on your entity:

public class MyEntity
{
    public int Id { get; set; }
    public string Name { get; set; }
    
    // Temporal period columns as real properties
    public DateTime ValidFrom { get; set; }
    public DateTime ValidTo { get; set; }
}

Your EF configuration stays the same:

config.ToTable("MyTable", "dbo", b => b.IsTemporal(b =>
{
    b.HasPeriodStart("ValidFrom");
    b.HasPeriodEnd("ValidTo");
}));

EF Core fully supports mapping period columns to real entity properties so the HasPeriodStart/HasPeriodEnd calls work identically whether the columns map to shadow or real properties.

Then your Facet DTO can work:

[Facet(typeof(MyEntity))]
public partial class MyEntityDto { }
// ValidFrom and ValidTo are generated automatically and included in the Projection

If you want to exclude them from certain DTOs, you can use the exclude pattern

But

If there's enough demand for keeping those columns as shadow properties (no C# property on the source), I could see adding something like an [EfShadowProperty] attribute for example:

[Facet(typeof(MyEntity))]
public partial class MyEntityDto
{
    [EfShadowProperty("ValidFrom")]
    public DateTime ValidFrom { get; set; }

    [EfShadowProperty("ValidTo")]
    public DateTime ValidTo { get; set; }
}

This would generate EF.Property<DateTime>(source, "ValidFrom") in the projection expression instead of source.ValidFrom. But honestly, i think making the period columns real properties on the entity is simpler and avoids the complexity entirely.

Let me know if this helps or if you have further questions!