[Cart Operations] Coupons

[misha-kotov]

As a Magento developer, I need to manipulate the shopping cart via GraphQL so that I can build basic ecommerce experiences for shoppers on the front-end using only GraphQL.

GraphQL needs to provide sufficient mutations (ways to create/update/delete data) for a developer to build out the storefront checkout experience for a shopper.

Use cases:

• Both guest and registered shoppers can add and remove coupon codes to/from their shopping cart

Acceptance criteria:

• Proposed schema is here
• GraphQL provides a mutation through which the coupons can be added/removed on a shopper's cart in checkout
• When a coupon is already applied to the cart and user tries to apply another, give an error message: "A coupon is already applied to the cart. Please remove it to apply another."
• Changes are covered with web API functional tests. See \Magento\GraphQl\Catalog\ProductViewTest::testQueryAllFieldsSimpleProduct as an example.

Assumptions:

• A coupon cannot be updated in place (only removed and re-added)
• A cart can have only one coupon applied at any time (Cannot add multiple coupon codes to the same cart)

My Account area impacted:

• Cart

[naydav]

#163