Event handlers

package:@deity/falcon-talonone-module

For our Falcon Platform module @deity/falcon-talonone-module to be able to syncronize customer and session data with Talon.One we needs to 'hook' into some data flows. Where we can we do this in a non-blocking way, preventing the user from waiting unnecicerly long for a request to finish. However, in some cases non-blocking syncronizations are simply not viable. For example, all cart syncronizations need to be done in a blocking way, since Talon.One will give us an updated set of promotional effects after each cart update. In Falcon Plaform we need to wait for this effects and apply them to the cart in the shop backend.

For example, when a customer fires the addToCart mutation the following flow will get's triggered under the hood by default;

1. Customer clicks add to cart in PWA, a addToCart GraphQl mutations gets called
2. Falcon Platform updates cart in shop backend
3. Our @deity/falcon-talonone-module waits for addToCart to finish and uploads latest cart snapshot to TalonOne CustomerSession
4. Talon.One return a set of effects. Falcon Platform transforms those effects to a set of Falcon DiscountRules
5. The active shop module takes those Falcon DiscountRules and maps them to the shops cart promotion format
6. Request addToCart is fully finished and will return success
7. PWA can now safely refetch cart query with latest promotional data

GQLOperationEventHandlers

To hook into shop operations inside the @deiy/falcon-talonone-module we can register event handlers before and after operations. When an error is thrown inside a beforeGQLOperationEventHandler handler the request will throw an exception and close the request before the actual query/mutation resolver get's called.

If we want to perform an action before a customer mutates the cart we can create 1 EventHandler who get's triggered before each addToCart, updateCartItem and removeCartItem mutation. We do this as follow;

import type { BeforeGraphQLOperationEventHandlerPayload } from '@deity/falcon-server-env';
import { EventHandler, beforeGQLOperationEventHandler } from '@deity/falcon-server-env';
import type { ShopHttpSession } from '@deity/falcon-shop-module';
import { inject } from 'inversify';

@beforeGQLOperationEventHandler('Mutation', 'addToCart')
@beforeGQLOperationEventHandler('Mutation', 'updateCartItem')
@beforeGQLOperationEventHandler('Mutation', 'removeCartItem')
export class MyCustomBeforeCartMutationEventHandler extends EventHandler<BeforeGraphQLOperationEventHandlerPayload> {
  constructor(@inject('ReadOnlyShopHttpSession') protected shopHttpSessionFactory: (httpSession) => ShopHttpSession) {
    super();
  }

  async execute(payload: BeforeGraphQLOperationEventHandlerPayload): Promise<void> {
    const { customerId, cartId } = this.shopHttpSessionFactory(payload.session);

    // Do something
  }
}

Inside this handler's execute method we can perform some (asynchronous) action, after which the query/mutation resolver will continue.

Bind EventHandlers

When adding event handlers we need to bind those for Falcon Platform to be able to find them. For more info on rebinding please check our Binding services docs

Default event handlers

In the module @deiy/falcon-talonone-module a few handlers are running out of the box for some basic syncronization functionalities between Talon.One and the configured shop backend;

EventHandler	Triggered
AfterAddressRemoveEventHandler	After Gql operation removeAddress
AfterEditCustomerEventHandler	After Gql operation editCustomer
AfterOrderUpdateEventHandler	ShopEvents.ORDER_STATUS_UPDATED
AfterSignInEventHandler	After Gql operation signIn
AfterSignupEventHandler	After Gql operation signUp
RemovePromotionFromCartEventHandler	Before Gql operation addToCart Before Gql operation updateCartItem Before Gql operation removeCartItem
SynchronizeCartWithTalonOneCustomerSessionEventHandler	After Gql operation addToCart After Gql operation updateCartItem After Gql operation removeCartItem
UpdateCustomerProfileDefaultAddressEventHandler	After Gql operation addAddress After Gql operation editAddress
ValidateCartWithTalonOneCustomerSessionEventHandler	Before Gql operation placeOrder