Event Handler

Description

Reacts to a specific type of Domain Event, performing side effects or triggering further actions.

Definition Schema

The definition for a event_handler component expects the following structure:

{
  "$defs": {
    "EventHandlerDependencyInputDTO": {
      "description": "Defines a dependency to be injected into the Event Handler's __init__.",
      "example": {
        "assigned_attribute_name": "_emailer",
        "param_name": "email_service",
        "param_type_str": "EmailService"
      },
      "example_with_explicit_import": {
        "param_import_from_module": "app_root_name.services.notifications",
        "param_import_names": [
          "NotificationService"
        ],
        "param_name": "notification_svc",
        "param_type_str": "NotificationService"
      },
      "properties": {
        "param_name": {
          "description": "Name of the parameter in __init__ (e.g., 'user_repository')",
          "title": "Param Name",
          "type": "string"
        },
        "param_type_str": {
          "description": "Type hint string for the parameter (e.g., 'UserRepository')",
          "title": "Param Type Str",
          "type": "string"
        },
        "assigned_attribute_name": {
          "anyOf": [
            {
              "type": "string"
            },
            {
              "type": "null"
            }
          ],
          "default": null,
          "description": "Name of the attribute to assign the dependency to on self (e.g., '_repo'). Defaults to '_' + param_name if None.",
          "title": "Assigned Attribute Name"
        },
        "param_import_from_module": {
          "anyOf": [
            {
              "type": "string"
            },
            {
              "type": "null"
            }
          ],
          "default": null,
          "description": "Optional: Explicit module to import the dependency type from (e.g., 'app_root_name.services.email').",
          "title": "Param Import From Module"
        },
        "param_import_names": {
          "anyOf": [
            {
              "items": {
                "type": "string"
              },
              "type": "array"
            },
            {
              "type": "null"
            }
          ],
          "default": null,
          "description": "Optional: Explicit list of names to import from the module (e.g., ['EmailService']). Used if param_import_from_module is set.",
          "title": "Param Import Names"
        }
      },
      "required": [
        "param_name",
        "param_type_str"
      ],
      "title": "EventHandlerDependencyInputDTO",
      "type": "object"
    }
  },
  "description": "DTO for defining an Event Handler class.",
  "example": {
    "dependencies": [],
    "event_bus_instance_name": "event_bus",
    "event_module": "generated_events",
    "event_name": "PostCreatedEvent",
    "name": "LogPostCreationHandler"
  },
  "example_with_deps": {
    "dependencies": [
      {
        "assigned_attribute_name": "_notifier",
        "param_name": "notification_service",
        "param_type_str": "NotificationService"
      }
    ],
    "event_bus_instance_name": "event_bus",
    "event_module": "generated_events",
    "event_name": "OrderPlacedEvent",
    "name": "NotifyAdminOnOrderPlacedHandler"
  },
  "properties": {
    "name": {
      "description": "Name of the handler class (e.g., 'LogPostCreationHandler')",
      "title": "Name",
      "type": "string"
    },
    "event_name": {
      "description": "Name of the event class it handles (e.g., 'PostCreatedEvent')",
      "title": "Event Name",
      "type": "string"
    },
    "event_module": {
      "description": "Module where the event class is defined (e.g., 'generated_events')",
      "title": "Event Module",
      "type": "string"
    },
    "dependencies": {
      "description": "List of dependencies for the __init__ method.",
      "items": {
        "$ref": "#/$defs/EventHandlerDependencyInputDTO"
      },
      "title": "Dependencies",
      "type": "array"
    },
    "event_bus_instance_name": {
      "default": "event_bus",
      "description": "Name of the event bus instance variable used for the @register decorator.",
      "title": "Event Bus Instance Name",
      "type": "string"
    }
  },
  "required": [
    "name",
    "event_name",
    "event_module"
  ],
  "title": "EventHandlerInputDTO",
  "type": "object"
}

Naming and Location Conventions

Class: PascalCase, typically ends with 'EventHandler'. File: ${event_handler_name}.py (based on ${event_handler_name}). Location: app/application/${bounded_ctx}/handlers. (Requires context: ['bounded_ctx'])

Example Definition

{
  "name": "LogPostCreationHandler",
  "event_name": "PostCreatedEvent",
  "event_module": "generated_events",
  "dependencies": [],
  "event_bus_instance_name": "event_bus"
}