ERP Market

Complete enterprise management system specifically designed for minimarkets and retail stores in Chile. Built with multi-tenant architecture that allows multiple companies to use the same instance with complete data isolation.

The Problem

Minimarkets in Chile face unique challenges: - Legal obligation to issue electronic receipts (SII) - Need to control inventory with multiple costing methods - Integration with specialized hardware (scales, thermal printers) - Continuous operation with zero downtime tolerance

Existing solutions were too expensive or didn't adapt to Chilean reality.

Solution

ERP Market is a comprehensive system covering the entire operation cycle:

Point of Sale (POS)

┌─────────────────────────────────────────────┐
│  Touch POS                                  │
├─────────────────────────────────────────────┤
│  [Product 1]  [Product 2]  [Product 3]      │
│  [Product 4]  [Product 5]  [Product 6]      │
├─────────────────────────────────────────────┤
│  Cart:                                      │
│  - Bread x2 ............ $1,200            │
│  - Milk x1 ............. $1,500            │
│  ─────────────────────────────              │
│  Total: $2,700                              │
├─────────────────────────────────────────────┤
│  [Cash] [Card] [Mixed]                      │
└─────────────────────────────────────────────┘

• Touch interface optimized for 10" screens
• Search by barcode, name, or internal code
• Integration with digital scales for weighable products
• Real-time thermal receipt printing

SII Electronic Invoicing

Complete integration with Chile's Internal Revenue Service:

• Automatic DTE (Electronic Tax Documents) generation
• Digital signature with .pfx certificate
• Automatic submission to SII with retries
• PDF generation with electronic stamp (TED)
• Support for: Receipts (39), Invoices (33), Credit Notes (61)

Inventory Management

Multi-Tenant Architecture

class CompanyBoundModel(models.Model):
    """All models inherit from here for isolation."""
    company = models.ForeignKey(Company, on_delete=models.CASCADE)

    class Meta:
        abstract = True

# Automatic middleware filters by user's company
class CompanyMiddleware:
    def __call__(self, request):
        if request.user.is_authenticated:
            _thread_locals.company = request.user.profile.company
        return self.get_response(request)

Tech Stack

• Backend: Django 4.2 with Django REST Framework
• Frontend: HTMX + Alpine.js (no SPA)
• Database: PostgreSQL with optimized indexes
• Async tasks: Celery + Redis
• PDF: WeasyPrint for tax documents
• Containers: Docker Compose for development and production

Results

• 0 data leaks between tenants in 2 years of operation
• < 200ms average response time in POS
• 99.9% production uptime
• 100% of receipts accepted by SII

Learnings

This project taught me the importance of:

1. Paranoid validation in multi-tenant systems
2. Robust error handling in external integrations
3. Offline-first design for critical operations
4. Exhaustive testing of invoicing flows