# Sequelize Models Summary

## ✅ All Models Created (20 Models)

### Core Models (3)
1. **Customer** - Customers (B2B, B2C) - Optional for walk-in sales
2. **Product** - Products (FG/RM) with description and default_vat_rate
3. **ProductVariant** - Product variants with JSON attributes

### Inventory Models (3)
4. **Inventory** - Quantity-based inventory (Layer 1)
5. **InventoryItem** - UID-based inventory (Layer 2) with barcode field
6. **InventoryMovement** - Inventory audit trail and sync

### Procurement Models (4)
7. **Vendor** - Suppliers (OPEN_MARKET/REGISTERED)
8. **PurchaseOrder** - Purchase orders (optional workflow)
9. **GRN** - Goods Receipt Notes (can exist without PO) with vendor_id
10. **GRNItem** - GRN items with quantities and costs

### Production Models (3)
11. **BOM** - Bill of Materials (Finished Good recipes)
12. **BOMItem** - BOM items (RM per FG unit)
13. **ProductionOrder** - Production runs with status tracking

### Sales Models (2)
14. **Sale** - Sales transactions (POS/Invoice) with optional customer
15. **SaleItem** - Sale items with **inventory_item_id** for UID traceability ⭐

### Payment & Fiscal Models (2)
16. **Payment** - Payments (multiple per sale) with provider tracking
17. **FiscalReceipt** - KRA eTIMS receipts (decoupled) with return_id ⭐

### Returns Models (2) - NEW ⭐
18. **Return** - Customer returns with status and total_amount
19. **ReturnItem** - Return items with UID traceability

### Utility Models (1)
20. **SystemLog** - System audit logs with user_id (optional)

---

## 🎯 Enhancements Added

1. **Product.description** - Added TEXT field for product descriptions
2. **Product.default_vat_rate** - Added DECIMAL(5,2) for default VAT rate (16% default)
3. **InventoryItem.barcode** - Added explicit barcode field (in addition to UID)
4. **GRN.vendor_id** - Added vendor_id for better tracking
5. **SaleItem.inventory_item_id** - Added for UID traceability (which specific UID was sold)
6. **FiscalReceipt.return_id** - Added to link credit notes to returns
7. **Return table** - NEW table for proper return tracking
8. **ReturnItem table** - NEW table for return items with UID traceability
9. **Return.reason** - Added TEXT field for return reasons

---

## 📊 Database Relationships

### Key Relationships:
- **Product** → ProductVariants, Inventories, InventoryItems, SaleItems, GRNItems, BOMItems
- **Sale** → Customer (optional), SaleItems, Payments, FiscalReceipts, Returns
- **InventoryItem** → Product, ProductVariant, SaleItems, ReturnItems
- **Return** → Sale, ReturnItems, FiscalReceipts (credit notes)
- **GRN** → PurchaseOrder (optional), Vendor, GRNItems
- **BOM** → ProductVariant (FG), BOMItems (RM)
- **ProductionOrder** → ProductVariant (FG)

---

## 🔗 All Associations Configured

All model associations are properly configured in `models/index.js`:
- BelongsTo relationships (many-to-one)
- HasMany relationships (one-to-many)
- Foreign key constraints with CASCADE/SET NULL as appropriate
- Aliases for cleaner query syntax

---

## 📝 Indexes Created

All models have appropriate indexes for:
- Foreign keys (faster joins)
- Unique constraints (SKUs, invoice numbers, UIDs)
- Frequently queried fields (status, dates, types)
- Composite indexes for common query patterns

---

## ✅ Schema Compliance

The models fully implement:
- ✅ Dual inventory model (quantity + UID)
- ✅ Optional customers (walk-ins)
- ✅ Open-market procurement (GRN without PO)
- ✅ BOM-based production
- ✅ Decoupled fiscal receipts
- ✅ Multiple payments per sale
- ✅ Return tracking with UID traceability
- ✅ Full audit trail (inventory movements + system logs)

---

## 🚀 Next Steps

1. Configure `.env` file with database credentials
2. Run `npm install` to ensure all dependencies are installed
3. Start server - models will sync automatically in development mode
4. Begin implementing service layer logic for each module

---

## 📁 File Structure

```
server/models/
├── index.js              # Sequelize setup & associations
├── Customer.js
├── Product.js
├── ProductVariant.js
├── Inventory.js
├── InventoryItem.js
├── InventoryMovement.js
├── Vendor.js
├── PurchaseOrder.js
├── GRN.js
├── GRNItem.js
├── BOM.js
├── BOMItem.js
├── ProductionOrder.js
├── Sale.js
├── SaleItem.js
├── Payment.js
├── FiscalReceipt.js
├── Return.js
├── ReturnItem.js
└── SystemLog.js
```

All models are fully commented and ready for use! 🎉

