How to Override Cart Completion Strategy
In this document, you’ll learn how to override the cart completion strategy.
This guide only explains how to override the cart completion strategy. It’s highly recommended to first understand how Medusa implements the cart completion strategy as explained here.
Step 1: Create Strategy Class
Create a TypeScript or JavaScript file in src/strategies of your Medusa backend project with a class that extends the AbstractCartCompletionStrategy class:
import {
AbstractCartCompletionStrategy,
CartCompletionResponse,
IdempotencyKey } from "@medusajs/medusa"
import {
RequestContext,
} from "@medusajs/medusa/dist/types/request"
class CartCompletionStrategy
extends AbstractCartCompletionStrategy {
complete(
cartId: string,
idempotencyKey: IdempotencyKey,
context: RequestContext
): Promise<CartCompletionResponse> {
throw new Error("Method not implemented.")
}
}
export default CartCompletionStrategy
The class includes the complete method defined as abstract in AbstractCartCompletionStrategy. At the moment, the method only throws an error.
Using a Constructor
You can use a constructor to access services and resources registered in the dependency container using dependency injection. For example:
// ...
import { IdempotencyKeyService } from "@medusajs/medusa"
type InjectedDependencies = {
idempotencyKeyService: IdempotencyKeyService
}
class CartCompletionStrategy
extends AbstractCartCompletionStrategy {
protected readonly idempotencyKeyService_:
IdempotencyKeyService
constructor(
{ idempotencyKeyService }: InjectedDependencies
) {
super(arguments[0])
this.idempotencyKeyService_ = idempotencyKeyService
}
// ...
}
export default CartCompletionStrategy
In the above example, you inject the IdempotencyKeyService in the constructor. This allows you to use the IdempotencyKeyService within your class.
Step 2: Implement the complete Method
The cart completion strategy is required to implement a single method: the complete method. This method is used in the Complete Cart endpoint to handle the logic of completing the cart.
The method accepts three parameters:
cartId: the first parameter of the method, which is a string indicating the ID of the cart to complete.idempotencyKey: the second parameter of the method, which is an instance of theIdempotencyKeyentity. The idempotency key is retrieved based on the idempotency key passed in the header of the request, and it’s used to determine the current point reached in the checkout flow to avoid inconsistencies on interruptions. You can learn more about the idempotency key here. You can also learn how to use it within your strategy by following this guidecontext: the third parameter of the method, which is an object that holds a single propertyip.ipis a string indicating the IP of the customer.
The completion strategy is expected to return an object with the following properties:
response_code: a number indicating the response code.response_body: an object that will be returned to the client.
You can refer to this guide to learn how the cart conceptual guide is implemented in the Medusa backend. This can help you understand how details such as inventory, taxes, and more are handled.
Step 3: Run Build Command
In the directory of the Medusa backend, run the build command to transpile the files in the src directory into the dist directory:
Test it Out
Run your backend to test it out:
Then, try out your strategy using the Complete Cart endpoint. You should see the logic you implemented used for completing the cart.