Enable change tracking

Turn on history or ledger on an entity.

Add [Tracked] for queryable history, [Ledger] for tamper-evident history.

using SmartData.Server.Attributes;
using LinqToDB.Mapping;

[Table]
[Tracked]                  // queryable history only
public class Product { /* ... */ }

[Table]
[Ledger]                   // history + hash chain (implies Tracked)
public class Invoice { /* ... */ }

That's the whole opt-in. On next startup, AutoRepo creates:

  • [Tracked] → Product_History table + _sys_tracked_columns sidecar
  • [Ledger] → Invoice_History + Invoice_Ledger + sidecar

From then on, every ctx.Insert / ctx.Update / ctx.Delete on the entity writes a history row (and, for ledger, a chain row) in the same transaction as the data row.

Exclude columns

Use [NotTracked] on properties that shouldn't be captured:

[Table]
[Tracked]
public class User
{
    [PrimaryKey, Identity, Column] public int Id { get; set; }
    [Column] public string Email { get; set; } = "";

    [Column, NotTracked] public string PasswordHash { get; set; } = "";  // not in history
    [Column, NotTracked] public string? SessionToken { get; set; }
}

No procedure changes needed

Writes go through the same entity APIs. Your CustomerSave procedure looks the same whether Customer is tracked or not. The capture is automatic.

Cost

Every tracked write has overhead:

  • [Tracked] → one extra row per write.
  • [Ledger] → two extra rows per write (_History + _Ledger), plus hash compute.

Reserve for entities where the audit trail pays for itself. Hot-path entities (events, metrics, sessions) should stay plain.

Verifying it's working

// Insert a row
var p = ctx.Insert(new Product { Name = "Widget", Price = 9.99m, CreatedBy = CurrentUser });

// History mirror appeared — read via ctx.History<T>(), not a generated companion type.
// Rows are HistoryEntity<Product> — the source entity sits on h.Data.
var firstHistory = ctx.History<Product>()
    .First(h => h.Data.Id == p.Id);
// h.Operation == "I" (I/U/D), h.ChangedBy == CurrentUser, h.ChangedOn ≈ now, h.Data == snapshot

Turning it off

Remove the attribute. Restart. Writes stop being captured. Existing history is preserved; nothing is dropped automatically. Use sp_tracking_drop / sp_ledger_drop if you want to remove the backing tables.