Tagging Reactors

Tags provide a way to organize and categorize your reactors for better discoverability and management. By applying the [Tag] attribute to your reactor classes, you can assign one or more tags that describe the purpose or domain of the reactor.

[Tag] and [Tags] label the reactor itself. They do not filter which appended events the reactor handles. For event filtering based on appended metadata, see Filter reducers and reactors by tag, Filter reducers and reactors by event source type, and Filter reducers and reactors by event stream type.

Adding Tags

You can tag reactors in multiple ways:

Single Tag

Apply a single tag to your reactor:

using Cratis.Chronicle;
using Cratis.Chronicle.Reactors;

[Tag("Notifications")]
public class OrderConfirmationReactor
{
    readonly IEmailService _emailService;

    public OrderConfirmationReactor(IEmailService emailService)
    {
        _emailService = emailService;
    }

    public async Task OnOrderPlaced(OrderPlaced @event, EventContext context)
    {
        await _emailService.SendOrderConfirmation(@event.CustomerId, @event.OrderId);
    }
}

Multiple Tags (Single Attribute)

Use the params feature to specify multiple tags in a single attribute:

[Tag("Notifications", "Customer", "Email")]
public class CustomerNotificationReactor
{
    readonly IEmailService _emailService;

    public CustomerNotificationReactor(IEmailService emailService)
    {
        _emailService = emailService;
    }

    public async Task OnCustomerRegistered(CustomerRegistered @event, EventContext context)
    {
        await _emailService.SendWelcomeEmail(@event.Email, @event.Name);
    }
}

Multiple Tags (Multiple Attributes)

Apply multiple [Tag] attributes:

[Tag("Integration")]
[Tag("ExternalAPI")]
[Tag("Inventory")]
public class InventorySyncReactor
{
    readonly IInventoryApi _inventoryApi;

    public InventorySyncReactor(IInventoryApi inventoryApi)
    {
        _inventoryApi = inventoryApi;
    }

    public async Task OnProductStockChanged(ProductStockChanged @event, EventContext context)
    {
        await _inventoryApi.UpdateStock(@event.ProductId, @event.NewQuantity);
    }
}

Mixed Approach

Combine both approaches:

[Tag("Notifications", "SMS")]
[Tag("Customer")]
public class SmsNotificationReactor
{
    readonly ISmsService _smsService;

    public SmsNotificationReactor(ISmsService smsService)
    {
        _smsService = smsService;
    }

    public async Task OnOrderShipped(OrderShipped @event, EventContext context)
    {
        await _smsService.SendShippingNotification(@event.PhoneNumber, @event.TrackingNumber);
    }
}

Best Practices

Use meaningful names: Choose tag names that clearly describe the purpose or domain
Be consistent: Establish tag naming conventions across your organization
Don't over-tag: Apply only relevant tags; too many can reduce their usefulness
Group related reactors: Use tags to group reactors that serve similar purposes

Common Tag Examples

Here are some common patterns for tagging reactors:

// By integration type
[Tag("Notifications")]
[Tag("ExternalAPI")]
[Tag("MessageQueue")]
[Tag("FileSystem")]

// By domain
[Tag("Sales")]
[Tag("Inventory")]
[Tag("Customer")]
[Tag("Shipping")]

// By communication channel
[Tag("Email")]
[Tag("SMS")]
[Tag("Push")]
[Tag("Webhook")]

// By purpose
[Tag("Integration")]
[Tag("Alerting")]
[Tag("Monitoring")]
[Tag("Automation")]

// By stakeholder
[Tag("Customer")]
[Tag("Operations")]
[Tag("Finance")]
[Tag("Support")]

Querying by Tag

Tags stored in the event store definition can be used for:

Filtering and searching for specific reactors
Organizing reactors in administrative interfaces
Generating documentation
Managing reactor deployments by tag
Monitoring and alerting based on tag groups
Controlling reactor activation by tag

Note: The specific querying capabilities depend on your Chronicle setup and tooling.

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