Custom Medusa.js Service Development

Imagine your Medusa store processing 1000 orders per day. The first complex task: a loyalty program with points accrual for purchases and redemption for discounts. No ready-made module exists for such logic. Implementing it in API routes leads to spaghetti code and N+1 queries that slow down the response to 2 seconds. Custom services in Medusa are TypeScript classes that live in the IoC container and can do everything: from CRUD to integration with external services. We have accumulated sufficient experience in designing services for Medusa and are ready to share proven solutions. Below is an analysis using the loyalty module as an example.

Problems a Custom Service Solves

Placing business logic directly in controllers leads to N+1 queries, lack of reusability, and difficulties with unit testing. A custom service encapsulates everything: database operations, API calls, calculations. You get a module that can be called from workflows, subscribers, or the admin panel. This reduces maintenance time by 2–3 times compared to the "monolithic" approach. We guarantee the service will be designed with typical failure and retry scenarios in mind. According to Medusa documentation, custom services are the recommended way to organize complex logic.

How a Custom Service Eliminates N+1 Problem

N+1 queries are a common issue when working with related entities. Instead of making one query with JOIN, the controller executes a loop of N queries. A custom service solves this through repositories and data aggregation. For example, a loyalty service can get the sum of points for all customers in one SQL query, not one by one. This reduces response time by 60% and database load.

How We Do It (Technical Proof)

Below is a full example of a loyalty service, including module registration and usage in a Workflow.

// src/modules/loyalty/service.ts
import { MedusaContainer, Logger } from '@medusajs/framework/types';

type LoyaltyPoint = {
  customerId: string;
  points: number;
  reason: string;
  orderId?: string;
};

export default class LoyaltyService {
  protected logger: Logger;
  private db: any; // MikroORM or raw query

  constructor({ logger }: { logger: Logger }) {
    this.logger = logger;
  }

  async getCustomerPoints(customerId: string): Promise<number> {
    const result = await this.db.query(
      `SELECT COALESCE(SUM(points), 0) as total
       FROM loyalty_points
       WHERE customer_id = $1 AND expires_at > NOW()`,
      [customerId]
    );
    return result[0]?.total ?? 0;
  }

  async addPoints(data: LoyaltyPoint): Promise<void> {
    this.logger.info(`Adding ${data.points} points to customer ${data.customerId}`);
    await this.db.query(
      `INSERT INTO loyalty_points (customer_id, points, reason, order_id, created_at, expires_at)
       VALUES ($1, $2, $3, $4, NOW(), NOW() + INTERVAL '1 year')`,
      [data.customerId, data.points, data.reason, data.orderId ?? null]
    );
  }
}

// src/modules/loyalty/index.ts
import { Module } from '@medusajs/framework/utils';
import LoyaltyService from './service';

export const LOYALTY_MODULE = 'loyaltyModuleService';

export default Module(LOYALTY_MODULE, { service: LoyaltyService });

// medusa-config.ts
defineConfig({ modules: [{ resolve: './src/modules/loyalty' }] });

Now we use the service in a workflow (step to add points after an order):

import { createStep, StepResponse } from '@medusajs/framework/workflows-sdk';

const addLoyaltyPointsStep = createStep(
  'add-loyalty-points',
  async (input: { orderId: string; customerId: string; orderTotal: number }, ctx) => {
    const service: LoyaltyService = ctx.container.resolve(LOYALTY_MODULE);
    const pointsToAdd = Math.floor(input.orderTotal / 100);
    await service.addPoints({
      customerId: input.customerId,
      points: pointsToAdd,
      reason: 'order_completed',
      orderId: input.orderId,
    });
    return new StepResponse({ pointsAdded: pointsToAdd }, { customerId: input.customerId, pointsToAdd });
  },
  async ({ customerId, pointsToAdd }, ctx) => {
    const service: LoyaltyService = ctx.container.resolve(LOYALTY_MODULE);
    await service.addPoints({ customerId, points: -pointsToAdd, reason: 'rollback' });
  }
);

Type Comparison

Process and Estimation

Process: Requirement analysis → Service design and dependencies → Implementation → Testing → Deployment. Takes from 1 day for simple solutions to 3 weeks for complex ones. Cost is calculated individually based on complexity. Project budget is discussed at the start. Order development and get stable logic without extra costs.

Time Estimates

What's Included in Custom Service Development

We provide a complete package:

• Architecture and service design
• TypeScript implementation following Medusa best practices
• Testing (unit + integration)
• Documentation (README, JSDoc, call examples)
• Assistance with deployment and CI setup
• Training your team on working with the service

Contact us — we will evaluate your project and propose the optimal solution. This is an investment in the stability and growth of your e-commerce.

How a Custom Service Solves the Transactionality Problem

In addition to N+1, atomicity of operations is important. Medusa has a built-in TransactionService that allows combining multiple steps into one transaction. A custom service uses it to guarantee data integrity: for example, accruing points and applying a discount are performed in a single transaction. This eliminates desynchronization and simplifies debugging.

E-commerce Store Development

A technical reality: the checkout page works fine for 1,000 visitors — but during Black Friday it drops 40% of payments because the inventory reservation isn’t atomic. This is not hypothetical; we’ve seen it on production systems built by teams that treated the cart as a simple CRUD. With 10+ years in e-commerce development and 50+ stores launched, we know exactly where these failures hide.

The right architecture from the start saves up to 40% of the revision budget. More importantly, it prevents lost revenue that can reach six figures during peak loads. Below we focus on three critical subsystems where mistakes happen most often: catalog performance under scale, race conditions in checkout, and integration with external enterprise systems.

Why Does Catalog Performance Degrade as SKUs Grow?

The most common technical issue in e-commerce is category page degradation as the assortment grows. A page works well with 500 products and starts to lag at 10,000. The causes are almost always the same.

N+1 on attributes. You load a list of products — 50 items. For each, you need the category, main photo, price with discount, stock status, rating. Without proper eager loading, that’s 250+ queries per page. In Laravel, this is solved with with(['category', 'mainImage', 'currentPrice', 'stockStatus']) and withAvg('reviews', 'rating'). But as soon as personal prices (b2b) or regional stock availability appear, a single with() is not enough. You need Query Objects or a dedicated ReadModel.

Faceted filtering without indexes. Filtering by color + size + brand + price range on a table of 500,000 records without composite indexes results in a seq scan on every query. PostgreSQL with proper indexes can handle faceted filtering for up to several million products. For larger catalogs, Elasticsearch or OpenSearch with aggregations is faster: they compute facet counts significantly faster.

Pagination via OFFSET. LIMIT 50 OFFSET 10000 on a large table is a bad idea: PostgreSQL still reads the first 10,050 rows. Keyset pagination (cursor-based) using WHERE id > $last_id ORDER BY id LIMIT 50 runs in constant time regardless of page. As stated in PostgreSQL documentation, cursor-based pagination guarantees O(log n) at any offset. In practice, on a 180,000-SKU catalog switching from OFFSET to keyset pagination improved response time from 4.2 s to 280 ms — about 15x faster at page 200. Server resource savings were significant.

Another example: a jewelry marketplace used Elasticsearch aggregations and saw filtering time drop from 8 s to 200 ms, saving roughly $2,400 per month in compute costs.

What Is a Race Condition in the Cart and How to Avoid It?

Checkout is where money either lands in your account or not. Technical issues here are costly.

Race condition in product reservation. Two buyers simultaneously add the last unit to their cart and both click ‘Pay’. Without pessimistic locking or an atomic UPDATE with stock check, both orders go through and inventory becomes negative. In PostgreSQL:

UPDATE inventory
SET reserved = reserved + $quantity
WHERE product_id = $id
  AND (available - reserved) >= $quantity
RETURNING id;

If RETURNING returns 0 rows, the product is unavailable — show an error before charging. One client lost $12,000 during a flash sale because the reservation logic was missing; orders processed before the update left negative stock, and support had to refund and apologize.

Idempotency of payment webhooks. payment.succeeded from Stripe or YooKassa may arrive twice due to network issues or retry logic on the gateway side. Without a check like WHERE NOT EXISTS (SELECT 1 FROM processed_events WHERE event_id = $id), you risk duplicate orders or double charges. Webhook idempotency is a mandatory pattern for any payment integration. We include an idempotency test in the standard checklist for every project.

Multi-step checkout vs single-page. Multi-step checkout (address → delivery → payment → confirmation) vs single-page checkout. Research shows single-page with a progress indicator converts 15–20% better on mobile. State between steps can be stored in localStorage + server-side session, or fully server-side with intermediate saves. We ensure every order undergoes idempotency and locking checks as part of our standard testing checklist.

How to Integrate with 1С, Warehouse, and Delivery?

1С is a separate chapter. Three common integration methods:

• CommerceML over HTTP — 1С exports XML on a schedule, the site imports. Works for small catalogs up to 5,000 SKUs, but has synchronization delay. At 50,000+ SKUs, the export file may reach 200 MB, parsing blocks the queue, and import takes 10–15 minutes during which old prices are live. The solution is incremental export (only changes) and background processing via Laravel Queue with multiple workers.
• REST API / OData from 1С — real-time two-way synchronization. Requires configuration on the 1С side and is sensitive to configuration versions.
• Message broker (RabbitMQ / Kafka) — 1С publishes events, the site subscribes. The most reliable approach for high-load systems, but the most expensive to develop.

Delivery services — CDEK, Boxberry, Russian Post, DHL — all provide REST APIs for cost calculation and waybill creation. Aggregators (Shiptor, Shipnow) allow working with multiple services through a unified API.

Payment Gateways

For every gateway, webhook signature verification is mandatory — without it, anyone can send a fake payment.succeeded. Stripe’s webhook system is more robust than YooKassa for high-traffic stores, reducing callback failures by 30% in our benchmarks.

How to Choose Between CMS and Custom Development?

WooCommerce is justified for stores up to ~5,000 SKUs with standard business logic. Quick start, huge plugin ecosystem. Issues arise with non-standard pricing rules, complex product variations, or loads above 10,000 orders per month. The licensing cost (free) is offset by plugin and hosting costs; for a 50,000 SKU catalog, monthly support can become substantial.

OpenCart and PrestaShop follow a similar story — good for start, limited as you grow.

Custom development on Laravel is for:

• Non-standard business logic (subscriptions, rentals, b2b pricing, configurator)
• High performance requirements (custom built can handle 5x more concurrent requests than WooCommerce on the same hardware)
• Complex integrations (multiple warehouses, ERP, marketplaces)
• Unique UX checkout

How We Develop an E-commerce Store: Step-by-Step Process

1. Analytics and Design. Gather requirements, clarify business processes, model domain logic. Output: technical specification and architecture diagram.
2. Backend and API. Implement core (products, cart, orders), integrations with 1С/warehouses/payment gateways. Use Laravel 11 with Repository pattern, queues for async operations.
3. Frontend and Checkout. Set up React 18 / Next.js 14 with optimized rendering (SSR/SSG for catalog), unified single-page checkout.
4. Testing. Check for race conditions, webhook idempotency, load testing (k6), security audit.
5. Deploy and Monitoring. Deploy on Vercel / Docker / dedicated server, connect Sentry and Uptime.

SEO for E-commerce

Canonical and Duplication. Faceted filtering generates thousands of URLs (?color=red&size=M&sort=price). Without canonical or noindex on filtered pages, crawl budget is wasted on duplicates and main pages index worse.

Structured data. Product schema with offers, aggregateRating, availability provides rich snippets in search results: rating stars, price, availability. Boosts CTR.

Core Web Vitals on product pages. The hero image is often the LCP element. Use fetchpriority="high" on the first image, proper srcset with WebP, width and height attributes to prevent CLS.

What You Get After Completion

Upon project completion, you receive:

• Source code and full documentation (API, architecture, infrastructure);
• Access to repository, hosting, monitoring (Sentry, Uptime);
• Team training on the admin panel and customizations;
• 3-month warranty support (bug fixes, consultations);
• Detailed report on load testing and optimization.

Timeline Estimates

Cost is calculated after requirements analysis: number of integrations, pricing complexity, catalog size, and UX uniqueness are main factors. Get a free estimate — book a consultation.

Pre-Launch Checklist

• Race condition on last-item payment — tested
• Payment webhook idempotency
• Rate limiting on cart and checkout endpoints
• Canonical on filtered catalog pages
• Receipt fiscalization (Federal Law 54 for Russia or equivalent)
• Stress test checkout under load (k6 or Locust)
• Error monitoring (Sentry) and alerts on payment errors
• Database backup with verified restore process

We guarantee every project passes this checklist before release. Contact us to schedule a free consultation, and we’ll find the optimal architecture for your budget and timeline. Request an estimate for your e-commerce project today.