Medusa Ecommerce Skill

Build modern ecommerce applications with Medusa v2's modular architecture.

Context7 Integration

Always use context7 MCP for up-to-date API documentation:

# Primary sources (use in order of preference)
mcp-cli call context7/resolve-library-id '{"libraryName": "medusajs"}'

# Recommended library IDs:
# - /websites/medusajs_learn      - Tutorials, getting started
# - /websites/medusajs_resources  - API reference, detailed docs
# - /llmstxt/medusajs_llms-full_txt - Comprehensive reference

Query pattern:

mcp-cli call context7/query-docs '{"libraryId": "/websites/medusajs_learn", "topic": "your topic"}'

Architecture Overview

┌─────────────────────────────────────────────────────────────────┐
│                         Medusa Application                       │
├─────────────────────────────────────────────────────────────────┤
│  API Layer        │  Admin Routes (/admin)                       │
│                   │  Store Routes (/store)                       │
│                   │  Custom Routes (/custom)                     │
├─────────────────────────────────────────────────────────────────┤
│  Workflows        │  Multi-step operations with compensation     │
├─────────────────────────────────────────────────────────────────┤
│  Commerce Modules │  Product │ Cart │ Order │ Payment │ etc.    │
├─────────────────────────────────────────────────────────────────┤
│  Infrastructure   │  Cache │ Events │ File │ Notification       │
├─────────────────────────────────────────────────────────────────┤
│  Database         │  PostgreSQL with MikroORM                    │
└─────────────────────────────────────────────────────────────────┘

Project Structure

my-medusa-store/
├── src/
│   ├── modules/           # Custom modules
│   │   └── my-module/
│   │       ├── index.ts
│   │       ├── service.ts
│   │       └── models/
│   ├── workflows/         # Custom workflows
│   ├── subscribers/       # Event subscribers
│   ├── api/              # API routes
│   │   ├── admin/
│   │   ├── store/
│   │   └── middlewares.ts
│   ├── admin/            # Admin UI extensions
│   │   ├── routes/
│   │   └── widgets/
│   └── links/            # Module links
├── medusa-config.ts
└── package.json

Quick Reference

Container Resolution

// In API routes, subscribers, workflows
const productService = container.resolve("product")
const query = container.resolve("query")

// Common services
// "product", "cart", "order", "customer", "pricing"
// "payment", "fulfillment", "inventory", "region"
// "query" - for Query/Graph operations
// "logger" - for logging

Query (Graph) Operations

import { Query } from "@medusajs/framework"

// Retrieve with relations
const { data: products } = await query.graph({
  entity: "product",
  fields: ["id", "title", "variants.*", "variants.prices.*"],
  filters: { id: productId }
})

// Pagination
const { data, metadata } = await query.graph({
  entity: "order",
  fields: ["*", "items.*"],
  pagination: { skip: 0, take: 20 }
})

Remote Query (Cross-Module)

import { useQueryGraphStep } from "@medusajs/medusa/core-flows"

// In workflows - query across linked modules
const { data } = await useQueryGraphStep({
  entity: "product",
  fields: ["*", "inventory_items.*"] // Linked data
})

Creating API Routes

// src/api/store/custom/route.ts
import { MedusaRequest, MedusaResponse } from "@medusajs/framework"

export const GET = async (req: MedusaRequest, res: MedusaResponse) => {
  const query = req.scope.resolve("query")
  // ... handle request
  res.json({ data })
}

export const POST = async (req: MedusaRequest, res: MedusaResponse) => {
  const body = req.body
  // ... handle request
  res.json({ success: true })
}

Protected Admin Routes

// src/api/admin/custom/route.ts
import { MedusaRequest, MedusaResponse } from "@medusajs/framework"
import { authenticate } from "@medusajs/medusa"

export const GET = async (req: MedusaRequest, res: MedusaResponse) => {
  // req.auth_context.actor_id contains admin user ID
  res.json({ data })
}

// Middleware applies authentication automatically for /admin routes

Creating Workflows

import { createWorkflow, createStep, StepResponse } from "@medusajs/framework/workflows-sdk"

const myStep = createStep(
  "my-step",
  async (input: { data: string }, { container }) => {
    const service = container.resolve("myService")
    const result = await service.doSomething(input.data)
    return new StepResponse(result, result.id) // data, compensateInput
  },
  async (id, { container }) => {
    // Compensation (rollback) logic
    const service = container.resolve("myService")
    await service.undoSomething(id)
  }
)

export const myWorkflow = createWorkflow("my-workflow", (input) => {
  const result = myStep(input)
  return result
})

Event Subscribers

// src/subscribers/order-placed.ts
import { SubscriberArgs, SubscriberConfig } from "@medusajs/framework"

export default async function orderPlacedHandler({
  event,
  container
}: SubscriberArgs<{ id: string }>) {
  const orderId = event.data.id
  const logger = container.resolve("logger")
  logger.info(`Order placed: ${orderId}`)
}

export const config: SubscriberConfig = {
  event: "order.placed"
}

Data Models

import { model } from "@medusajs/framework/utils"

const MyModel = model.define("my_model", {
  id: model.id().primaryKey(),
  name: model.text(),
  description: model.text().nullable(),
  metadata: model.json().nullable(),
  is_active: model.boolean().default(true),
  created_at: model.dateTime(),
})

export default MyModel

Module Links

// src/links/product-custom.ts
import { defineLink } from "@medusajs/framework/utils"
import ProductModule from "@medusajs/medusa/product"
import MyModule from "../modules/my-module"

export default defineLink(
  ProductModule.linkable.product,
  MyModule.linkable.myModel
)

Common Operations

Create Product with Variants

const product = await productService.createProducts({
  title: "T-Shirt",
  options: [{ title: "Size", values: ["S", "M", "L"] }],
  variants: [
    { title: "Small", options: { Size: "S" }, prices: [{ amount: 1000, currency_code: "usd" }] },
    { title: "Medium", options: { Size: "M" }, prices: [{ amount: 1000, currency_code: "usd" }] },
  ]
})

Cart to Order Flow

// 1. Create cart
const cart = await cartService.createCarts({ region_id, currency_code: "usd" })

// 2. Add items
await cartService.addLineItems(cart.id, [{ variant_id, quantity: 1 }])

// 3. Add shipping/payment
await cartService.addShippingMethods(cart.id, [{ shipping_option_id }])
await paymentService.createPaymentCollections({ cart_id: cart.id })

// 4. Complete checkout (via workflow)
import { completeCartWorkflow } from "@medusajs/medusa/core-flows"
await completeCartWorkflow(container).run({ input: { id: cart.id } })

Payment Integration

// Initialize payment session
const paymentCollection = await paymentService.createPaymentCollections({
  cart_id: cartId,
  amount: cart.total,
  currency_code: cart.currency_code,
})

await paymentService.createPaymentSession(paymentCollection.id, {
  provider_id: "stripe", // or your provider
  data: { /* provider-specific */ }
})

CLI Commands

# Development
npx medusa develop          # Start dev server with admin

# Database
npx medusa db:migrate       # Run migrations
npx medusa db:generate      # Generate migration from models
npx medusa db:sync-links    # Sync module links

# Build
npx medusa build            # Production build
npx medusa start            # Start production server

Reference Files

Detailed documentation organized by topic:

Best Practices

1. Use workflows for multi-step operations - Built-in compensation handles failures
2. Query with query.graph() - Efficient data fetching with relations
3. Extend, don't modify - Create custom modules instead of modifying core
4. Use module links - Connect custom data to core entities
5. Validate at API layer - Use Zod schemas for request validation
6. Subscribe to events - React to changes asynchronously

Troubleshooting

Module not found: Ensure module is registered in medusa-config.ts

Link not working: Run npx medusa db:sync-links after adding links

Migration issues: Check model definitions match database schema

Type errors: Regenerate types with npx medusa generate:types