medusa-cart-checkout

Medusa v2 Cart and Checkout

Before writing code

Fetch live docs:

1. Web-search site:docs.medusajs.com cart module for cart data model and service methods
2. Web-search site:docs.medusajs.com checkout flow for the end-to-end checkout process
3. Web-search site:docs.medusajs.com sales channel for sales channel scoping
4. Fetch https://docs.medusajs.com/resources/references/cart and review the ICartModuleService interface
5. Web-search medusajs v2 cart workflow 2026 for latest cart-related workflow steps

Cart Lifecycle

Flow

Create Cart ──> Add Line Items ──> Set Address
  ──> Select Shipping ──> Init Payment ──> Complete

Cart States

| State | Description | |-------|-------------| | Active | Cart is open, items can be added/removed | | Completing | Checkout in progress, payment being processed | | Completed | Cart converted to order, no further modifications |

Cart Data Model

| Entity | Key Fields | |--------|------------| | Cart | region_id, customer_id, sales_channel_id, email | | LineItems[] | variant_id, quantity, unit_price, Adjustments[] | | ShippingMethods[] | shipping_option_id, amount, data | | Addresses | shipping_address, billing_address | | PaymentCollection | PaymentSessions[] |

Module Architecture

| Link Target | Purpose | |-------------|---------| | Product Module | Variant resolution | | Region Module | Currency, tax rules | | Sales Channel Module | Storefront scoping | | Promotion Module | Discount application | | Payment Module | Payment sessions | | Fulfillment Module | Shipping methods |

Fetch live docs for cross-module link definitions and remoteQuery usage for cart enrichment.

Checkout Steps

Step 1: Create Cart

// Skeleton: create cart in storefront
// Fetch live docs for createCartWorkflow input
const cart = await createCartWorkflow(container)
  .run({ input: { region_id, sales_channel_id } })
// Fetch live docs for required vs optional fields

Step 2: Add Line Items

| Workflow | Purpose | |----------|---------| | addToCartWorkflow | Add variant + quantity to cart | | updateLineItemInCartWorkflow | Update quantity of existing item | | deleteLineItemsWorkflow | Remove items from cart |

Step 3: Set Addresses

| Field | Required | Notes | |-------|----------|-------| | first_name / last_name | Yes | | | address_1 | Yes | Street address | | city | Yes | | | country_code | Yes | ISO 2-letter code | | postal_code | Conditional | Required by region | | province | Conditional | State/province |

Step 4: Select Shipping Option

Available options determined by cart region, shipping address, and shipping profiles.

| Workflow | Purpose | |----------|---------| | listShippingOptionsForCartWorkflow | Fetch available options | | addShippingMethodToCartWorkflow | Apply selected shipping option |

Step 5: Initialize Payment

| Workflow | Purpose | |----------|---------| | createPaymentCollectionForCartWorkflow | Create payment collection | | initializePaymentSessionWorkflow | Start provider-specific session |

Step 6: Complete Cart

| Workflow | Purpose | |----------|---------| | completeCartWorkflow | Convert cart to order |

Completion validates: all items in stock, shipping selected, payment authorized, email set.

Fetch live docs for the exact validation checks performed during cart completion.

Sales Channels

| Concept | Description | |---------|-------------| | Sales Channel | Named storefront scope (e.g., "Web", "Mobile App", "B2B") | | Publishable API Key | Associates Store API requests with a sales channel | | Product-Channel Link | Products published to specific channels |

• Each cart belongs to one sales channel
• Store API requests must include x-publishable-api-key header
• Products not linked to the cart's channel are unavailable

Fetch live docs for publishable API key configuration and sales channel management.

Store API Routes

| Route Pattern | Method | Purpose | |---------------|--------|---------| | /store/carts | POST | Create cart | | /store/carts/:id | GET | Retrieve cart | | /store/carts/:id | POST | Update cart (email, address) | | /store/carts/:id/line-items | POST | Add line item | | /store/carts/:id/line-items/:item_id | POST/DELETE | Update/remove line item | | /store/carts/:id/shipping-methods | POST | Add shipping method | | /store/carts/:id/payment-collections | POST | Create payment collection | | /store/carts/:id/complete | POST | Complete checkout |

Fetch live docs for request body shapes and response formats on each route.

Best Practices

Cart Management

• Always create carts with a region_id -- it determines currency, tax rules, and shipping
• Use sales_channel_id to scope product availability per storefront
• Store custom checkout data in cart metadata (e.g., gift messages, notes)

Checkout Flow

• Validate addresses before shipping option selection -- options depend on the destination
• Re-fetch shipping options after address changes (available options may differ)
• Initialize payment sessions only after shipping is selected (total must include shipping)
• Handle cart completion errors gracefully -- display specific validation failures to the user

Performance

• Use remoteQuery to enrich cart data (product details, images) in a single query
• Cache shipping options per region + address combination to reduce API calls

Security

• Never expose payment session secrets to the client
• Validate cart ownership (customer or anonymous session) on every mutation
• Use publishable API keys to enforce sales channel scoping

Fetch the Medusa v2 cart module documentation and checkout workflow references for exact service method signatures, workflow inputs, and validation rules before implementing.