docs(order): Add comprehensive order feature implementation summary

- Document complete order management feature implementation with database schema design
- Include overview of three PostgreSQL tables (sales_orders, sales_order_items, sales_order_addresses) with UUID primary keys
- Detail SQLAlchemy models, service layer methods, and API endpoints for order operations
- List Pydantic schemas for request/response validation
- Explain authentication flow using JWT tokens from auth-ms
- Document database migration scripts and rollback procedures
- Outline key technical decisions including no FK constraints, no SQLAlchemy relationships, and UUID usage
- Provide API standards compliance details for projection list support and POST method for lists
- Include testing approach and HuggingFace Space deployment information
- Document all created and modified files
- Add known issues and solutions section for troubleshooting

ORDER_FEATURE_IMPLEMENTATION_SUMMARY.md

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+# E-commerce Order Feature - Implementation Summary
+
+## Overview
+Complete order management feature for capturing and managing customer orders in the e-commerce microservice.
+
+## Implementation Date
+February 7, 2026
+
+## Components Implemented
+
+### 1. Database Tables (PostgreSQL - trans schema)
+
+Created three tables in the `trans` schema:
+
+#### trans.sales_orders
+Main order table with:
+- UUID primary key (sales_order_id)
+- Customer information (customer_id as UUID)
+- Merchant information (merchant_id as UUID)
+- Financial details (subtotal, tax, grand_total)
+- Payment information (status, method, amounts)
+- Fulfillment tracking (status, delivery dates)
+- Invoice details (invoice_id as UUID)
+- Audit fields (created_by, created_at, updated_at)
+
+#### trans.sales_order_items
+Order line items with:
+- UUID primary key (id)
+- Reference to sales_order (sales_order_id as UUID)
+- Product details (product_id, name, SKU)
+- Pricing (quantity, unit_price, tax, discount)
+- Additional info (HSN code, UOM, batch, serials)
+
+#### trans.sales_order_addresses
+Shipping and billing addresses with:
+- UUID primary key (id)
+- Reference to sales_order (sales_order_id as UUID)
+- Address type (shipping/billing)
+- Complete address fields
+
+**Key Design Decisions:**
+- All ID fields use UUID type (not VARCHAR ULID)
+- NO foreign key constraints (managed at application level)
+- All tables in `trans` schema
+- branch_id removed (not needed for e-commerce)
+
+### 2. SQLAlchemy Models
+
+Location: `app/order/models/model.py`
+
+Three models mapping to database tables:
+- `SalesOrder` - Main order model
+- `SalesOrderItem` - Order line items
+- `SalesOrderAddress` - Addresses
+
+**Important:** NO relationship() declarations to avoid FK constraint issues.
+
+### 3. Service Layer
+
+Location: `app/order/services/service.py`
+
+Key methods:
+- `create_order()` - Create new order with validation
+- `get_order()` - Retrieve order by ID
+- `list_orders()` - List orders with filtering and projection
+
+**Features:**
+- Product validation from MongoDB (scm_catalogues)
+- Single merchant per order validation
+- Automatic tax calculation
+- Order number generation (ORD-YYYYMMDD-NNNN)
+- UUID conversion and validation
+- Manual loading of related items and addresses (no relationships)
+
+### 4. API Endpoints
+
+Location: `app/order/controllers/router.py`
+
+#### POST /orders/create
+- Creates new order from customer request
+- Requires customer JWT authentication
+- Validates products and calculates totals
+- Returns complete order details
+
+#### GET /orders/{order_id}
+- Retrieves specific order by ID
+- Customer can only access their own orders
+
+#### GET /orders/
+- Simple list endpoint with pagination
+- Returns all orders for authenticated customer
+
+#### POST /orders/list
+- Advanced list endpoint with projection support
+- Follows API list endpoint standard
+- Supports filtering, sorting, pagination
+- Projection list for optimized responses
+
+### 5. Pydantic Schemas
+
+Location: `app/order/schemas/schema.py`
+
+Request schemas:
+- `CreateOrderRequest` - Order creation payload
+- `OrderItemRequest` - Item in order
+- `OrderAddressRequest` - Address information
+- `OrderListRequest` - List with filters and projection
+
+Response schemas:
+- `OrderResponse` - Complete order details
+- `OrderItemResponse` - Item details
+- `OrderAddressResponse` - Address details
+- `OrderListResponse` - Paginated list response
+
+## Authentication
+
+Uses JWT token from auth-ms:
+- Customer ID extracted from token
+- Token validated via `get_current_customer` dependency
+- Customer can only access their own orders
+
+## Database Migrations
+
+### Migration Scripts
+
+1. **001_create_ecommerce_order_tables.sql**
+   - Creates all three tables with UUID types
+   - No FK constraints
+   - Proper indexes on key fields
+
+2. **002_alter_existing_order_tables_to_uuid.sql**
+   - Alters existing tables to use UUID
+   - Converts VARCHAR(26) to UUID
+   - Removes branch_id column
+
+3. **001_rollback_ecommerce_order_tables.sql**
+   - Rollback script to drop tables
+
+### Running Migrations
+
+```bash
+# From cuatrolabs-ecomm-ms directory
+psql $POSTGRES_URI -f db/migrations/001_create_ecommerce_order_tables.sql
+
+# Or use the migration runner
+python db/run_migration.py
+```
+
+## Key Technical Decisions
+
+### 1. No Foreign Key Constraints
+Per user requirement, all FK constraints removed:
+- Allows flexibility in data management
+- Prevents cascade issues
+- Application-level referential integrity
+
+### 2. No SQLAlchemy Relationships
+To avoid FK dependency issues:
+- Removed all `relationship()` declarations
+- Manual loading of related data in service layer
+- Separate queries for items and addresses
+
+### 3. UUID for All IDs
+Changed from VARCHAR(26) ULID to UUID:
+- customer_id: UUID
+- merchant_id: UUID
+- sales_order_id: UUID
+- invoice_id: UUID
+- All item and address IDs: UUID
+
+### 4. Manual Relationship Loading
+Service layer manually loads related data:
+```python
+# Load items
+items_result = await session.execute(
+    select(SalesOrderItem).where(
+        SalesOrderItem.sales_order_id == order_uuid
+    )
+)
+items = items_result.scalars().all()
+
+# Load addresses
+addresses_result = await session.execute(
+    select(SalesOrderAddress).where(
+        SalesOrderAddress.sales_order_id == order_uuid
+    )
+)
+addresses = addresses_result.scalars().all()
+```
+
+## API Standards Compliance
+
+### Projection List Support
+Following the API list endpoint standard:
+- `projection_list` parameter in list requests
+- Returns only requested fields when projection used
+- Reduces payload size (50-90% reduction possible)
+- Better performance
+
+Example:
+```json
+{
+  "projection_list": [
+    "sales_order_id",
+    "order_number",
+    "status",
+    "grand_total"
+  ]
+}
+```
+
+### POST Method for Lists
+All list endpoints use POST (not GET) for:
+- Complex filtering
+- Projection support
+- Consistent API pattern
+
+## Testing
+
+Test script: `test_order_flow_complete.py`
+
+Tests:
+1. Customer token retrieval
+2. Order creation
+3. Order retrieval by ID
+4. Simple order listing (GET)
+5. Advanced listing with projection (POST)
+6. UUID validation
+
+## Deployment
+
+### HuggingFace Space
+Service deployed at: `https://cuatrolabs-cuatrolabs-ecomm-ms.hf.space`
+
+### Auto-deployment
+Changes pushed to main branch trigger automatic rebuild:
+```bash
+git add .
+git commit -m "message"
+git push origin main
+```
+
+## Files Modified/Created
+
+### Created
+- `app/order/models/model.py` - SQLAlchemy models
+- `app/order/schemas/schema.py` - Pydantic schemas
+- `app/order/services/service.py` - Business logic
+- `app/order/controllers/router.py` - API endpoints
+- `db/migrations/001_create_ecommerce_order_tables.sql`
+- `db/migrations/002_alter_existing_order_tables_to_uuid.sql`
+- `db/migrations/001_rollback_ecommerce_order_tables.sql`
+- `test_order_flow_complete.py` - Integration test
+
+### Modified
+- `app/main.py` - Router registration
+- `app/sql.py` - Model imports for schema validation
+
+## Known Issues & Solutions
+
+### Issue: SQLAlchemy Relationship Error
+**Problem:** "Could not determine join condition between parent/child tables"
+
+**Cause:** SQLAlchemy trying to use relationships without FK constraints
+
+**Solution:** 
+1. Remove all `relationship()` declarations from models
+2. Implement manual loading in service layer
+3. Clear `__pycache__` directories
+4. Redeploy service
+
+### Issue: UUID Format Errors
+**Problem:** "value too long for type character varying(26)"
+
+**Cause:** Database columns still using VARCHAR(26) instead of UUID
+
+**Solution:**
+1. Run migration script to alter columns to UUID type
+2. Update service layer to convert string IDs to UUID objects
+3. Validate UUID format before database operations
+
+## Future Enhancements
+
+1. **Order Status Workflow**
+   - Add state machine for order status transitions
+   - Webhook notifications on status changes
+
+2. **Payment Integration**
+   - Integrate with payment gateway
+   - Handle payment callbacks
+   - Update payment status automatically
+
+3. **Inventory Management**
+   - Reserve inventory on order creation
+   - Release on cancellation
+   - Update stock on fulfillment
+
+4. **Order Cancellation**
+   - Add cancel order endpoint
+   - Refund processing
+   - Inventory restoration
+
+5. **Order History**
+   - Track all status changes
+   - Audit trail for modifications
+   - Customer notifications
+
+## References
+
+- API Standards: `cuatrolabs-scm-ms/API_STANDARDS.md`
+- Projection Guide: `cuatrolabs-scm-ms/PROJECTION_LIST_IMPLEMENTATION.md`
+- Order API Quick Ref: `ORDER_API_QUICK_REF.md`
+- Setup Guide: `START_ORDER_SERVICE.md`
+
+## Support
+
+For issues or questions:
+1. Check logs: `cuatrolabs-ecomm-ms/logs/`
+2. Review test script: `test_order_flow_complete.py`
+3. Verify database schema: Run migration scripts
+4. Check HuggingFace Space logs for deployment issues