# Audit columns

Track when rows are created and last changed with server-side defaults and a small update hook.

Most tables benefit from `created_at` and `updated_at` columns. The created timestamp is a pure database default; the updated timestamp needs a touch on each write.

## Created timestamp

`[Default(DbDefaults.Time.Now)]` stamps the row server-side on insert, so the application never sets it:

```csharp
[Default(DbDefaults.Time.Now)]
public DateTime CreatedAt { get; set; }
```

`DbDefaults.Time.Now` is portable: the generator emits the platform's UTC-now expression in the DDL. See [DB constants](/database/0.3.2/advanced/db-constants).

## Updated timestamp

Set `UpdatedAt` before every update. Centralize it so no call site forgets:

```csharp
[Default(DbDefaults.Time.Now)]
public DateTime UpdatedAt { get; set; }

// in your service / repository
public Task<int> SaveAsync(TaskItem task) =>
    db.ExecuteAsync(d =>
    {
        task.UpdatedAt = DateTime.UtcNow;
        return d.Tasks.UpdateAsync(task);
    });
```

`UpdateAsync` writes every non-key column by default, so `updated_at` is included with no extra configuration.

## Who changed it

To record an actor, add a column and set it from your request context:

```csharp
public Guid? UpdatedBy { get; set; }
```

```csharp
task.UpdatedAt = DateTime.UtcNow;
task.UpdatedBy = currentUserId;
await d.Tasks.UpdateAsync(task);
```

> **TIP** If you want the timestamp enforced even for writes that bypass the application, keep the C# touch for convenience and add a database trigger as the source of truth. The `[Default]` expression handles inserts; a `BEFORE UPDATE` trigger handles updates. A [value convertor](/database/0.3.2/advanced/value-convertors) is the place to normalize an audit value (for example forcing UTC) on the way to the column.