Building an E-commerce Backend

Learn how to build a complete e-commerce backend with inventory management, order processing, payment integration, notifications, and automated workflows using Ductape SDK.

What You'll Build

• Product inventory management
• Shopping cart and order processing
• Stripe payment integration
• Email and SMS notifications
• Order fulfillment workflows
• Inventory tracking and alerts
• Customer management
• Order status updates
• Automated email campaigns

Prerequisites

• Node.js and npm installed
• Ductape account and API credentials
• Stripe account for payments
• Basic understanding of TypeScript/JavaScript
• Express.js knowledge (optional)

Setup

npm install @ductape/sdk express dotenv
npm install --save-dev @types/express @types/node typescript

Create .env:

DUCTAPE_API_KEY=your_api_key
STRIPE_SECRET_KEY=your_stripe_secret_key
STRIPE_WEBHOOK_SECRET=your_webhook_secret

Initialize Ductape SDK

import { Ductape } from '@ductape/sdk';
import express from 'express';

const ductape = new Ductape({
  apiKey: process.env.DUCTAPE_API_KEY!
});

const app = express();
app.use(express.json());

Database Schema

// Products table
await ductape.databases.schema.create('products', {
  sku: { type: 'String', unique: true, required: true },
  name: { type: 'String', required: true },
  description: { type: 'String' },
  price: { type: 'Number', required: true },
  compare_at_price: { type: 'Number' },
  cost_price: { type: 'Number' },
  currency: { type: 'String', default: 'USD' },
  category: { type: 'String' },
  tags: { type: 'Array' },
  images: { type: 'Array' },
  inventory_quantity: { type: 'Number', default: 0 },
  low_stock_threshold: { type: 'Number', default: 10 },
  is_active: { type: 'Boolean', default: true },
  is_featured: { type: 'Boolean', default: false },
  weight: { type: 'Number' }, // in grams
  dimensions: { type: 'JSON' }, // { length, width, height }
  created_at: { type: 'Date', default: 'now' },
  updated_at: { type: 'Date', default: 'now' }
});

// Customers table
await ductape.databases.schema.create('customers', {
  email: { type: 'String', unique: true, required: true },
  first_name: { type: 'String', required: true },
  last_name: { type: 'String', required: true },
  phone: { type: 'String' },
  stripe_customer_id: { type: 'String', unique: true },
  addresses: { type: 'Array' },
  default_address_index: { type: 'Number', default: 0 },
  total_orders: { type: 'Number', default: 0 },
  total_spent: { type: 'Number', default: 0 },
  marketing_opt_in: { type: 'Boolean', default: false },
  created_at: { type: 'Date', default: 'now' },
  updated_at: { type: 'Date', default: 'now' }
});

// Orders table
await ductape.databases.schema.create('orders', {
  order_number: { type: 'String', unique: true, required: true },
  customer_id: { type: 'String', required: true },
  email: { type: 'String', required: true },
  line_items: { type: 'Array', required: true },
  subtotal: { type: 'Number', required: true },
  tax: { type: 'Number', default: 0 },
  shipping_cost: { type: 'Number', default: 0 },
  discount: { type: 'Number', default: 0 },
  total: { type: 'Number', required: true },
  currency: { type: 'String', default: 'USD' },
  status: { type: 'String', default: 'pending' }, // pending, processing, fulfilled, cancelled
  payment_status: { type: 'String', default: 'pending' }, // pending, paid, refunded, failed
  fulfillment_status: { type: 'String', default: 'unfulfilled' },
  stripe_payment_intent_id: { type: 'String' },
  shipping_address: { type: 'JSON', required: true },
  billing_address: { type: 'JSON', required: true },
  tracking_number: { type: 'String' },
  shipped_at: { type: 'Date' },
  delivered_at: { type: 'Date' },
  notes: { type: 'String' },
  created_at: { type: 'Date', default: 'now' },
  updated_at: { type: 'Date', default: 'now' }
});

// Inventory transactions table
await ductape.databases.schema.create('inventory_transactions', {
  product_id: { type: 'String', required: true },
  sku: { type: 'String', required: true },
  quantity_change: { type: 'Number', required: true },
  type: { type: 'String', required: true }, // sale, restock, adjustment, return
  reference_id: { type: 'String' }, // order_id or purchase_order_id
  notes: { type: 'String' },
  created_at: { type: 'Date', default: 'now' }
});

// Create indexes
await ductape.databases.schema.createIndex('products', ['sku']);
await ductape.databases.schema.createIndex('products', ['category']);
await ductape.databases.schema.createIndex('products', ['is_active']);
await ductape.databases.schema.createIndex('customers', ['email']);
await ductape.databases.schema.createIndex('customers', ['stripe_customer_id']);
await ductape.databases.schema.createIndex('orders', ['order_number']);
await ductape.databases.schema.createIndex('orders', ['customer_id']);
await ductape.databases.schema.createIndex('orders', ['status']);
await ductape.databases.schema.createIndex('inventory_transactions', ['product_id']);

Product Management

// Create product
async function createProduct(productData: {
  sku: string;
  name: string;
  description: string;
  price: number;
  cost_price?: number;
  category?: string;
  inventory_quantity?: number;
  images?: string[];
}) {
  const result = await ductape.databases.insert({
    table: 'products',
    data: {
      sku: productData.sku,
      name: productData.name,
      description: productData.description,
      price: productData.price,
      cost_price: productData.cost_price,
      category: productData.category,
      inventory_quantity: productData.inventory_quantity || 0,
      images: productData.images || [],
      low_stock_threshold: 10
    }
  });

  return result.rows[0];
}

// Update inventory with transaction tracking
async function updateInventory(
  productId: string,
  quantityChange: number,
  type: 'sale' | 'restock' | 'adjustment' | 'return',
  referenceId?: string,
  notes?: string
) {
  // Get current product
  const product = await ductape.databases.findOne({
    table: 'products',
    where: { id: productId }
  });

  if (!product.row) {
    throw new Error('Product not found');
  }

  const newQuantity = product.row.inventory_quantity + quantityChange;

  if (newQuantity < 0) {
    throw new Error('Insufficient inventory');
  }

  // Update product inventory
  await ductape.databases.update({
    table: 'products',
    where: { id: productId },
    data: {
      inventory_quantity: newQuantity,
      updated_at: new Date()
    }
  });

  // Create inventory transaction record
  await ductape.databases.insert({
    table: 'inventory_transactions',
    data: {
      product_id: productId,
      sku: product.row.sku,
      quantity_change: quantityChange,
      type,
      reference_id: referenceId,
      notes
    }
  });

  // Check for low stock and send notification
  if (newQuantity <= product.row.low_stock_threshold && quantityChange < 0) {
    await sendLowStockNotification(product.row);
  }

  return newQuantity;
}

// Low stock notification
async function sendLowStockNotification(product: any) {
  await ductape.notifications.send({
    channel: 'email',
    to: 'inventory@yourstore.com',
    template: 'low-stock-alert',
    data: {
      product_name: product.name,
      sku: product.sku,
      current_quantity: product.inventory_quantity,
      threshold: product.low_stock_threshold
    }
  });
}

Customer Management with Stripe

// Create or get customer
async function createOrGetCustomer(customerData: {
  email: string;
  first_name: string;
  last_name: string;
  phone?: string;
  address?: any;
}) {
  // Check if customer exists
  const existing = await ductape.databases.findOne({
    table: 'customers',
    where: { email: customerData.email }
  });

  if (existing.row) {
    return existing.row;
  }

  // Create Stripe customer
  const stripeCustomer = await ductape.actions.execute({
    action: 'stripe.create-customer',
    input: {
      email: customerData.email,
      name: `${customerData.first_name} ${customerData.last_name}`,
      phone: customerData.phone,
      address: customerData.address,
      metadata: {
        source: 'ecommerce-api'
      }
    }
  });

  // Create customer in database
  const customer = await ductape.databases.insert({
    table: 'customers',
    data: {
      email: customerData.email,
      first_name: customerData.first_name,
      last_name: customerData.last_name,
      phone: customerData.phone,
      stripe_customer_id: stripeCustomer.id,
      addresses: customerData.address ? [customerData.address] : []
    }
  });

  return customer.rows[0];
}

Order Processing with Workflow

// Create order
async function createOrder(orderData: {
  customer_email: string;
  line_items: Array<{ product_id: string; quantity: number; price: number }>;
  shipping_address: any;
  billing_address: any;
}) {
  // Calculate totals
  const subtotal = orderData.line_items.reduce(
    (sum, item) => sum + item.price * item.quantity,
    0
  );
  const tax = subtotal * 0.1; // 10% tax
  const shipping_cost = subtotal > 100 ? 0 : 10; // Free shipping over $100
  const total = subtotal + tax + shipping_cost;

  // Generate order number
  const orderNumber = `ORD-${Date.now()}-${Math.random().toString(36).substr(2, 6).toUpperCase()}`;

  // Get or create customer
  const customer = await createOrGetCustomer({
    email: orderData.customer_email,
    first_name: orderData.shipping_address.first_name,
    last_name: orderData.shipping_address.last_name,
    phone: orderData.shipping_address.phone,
    address: orderData.shipping_address
  });

  // Create order
  const order = await ductape.databases.insert({
    table: 'orders',
    data: {
      order_number: orderNumber,
      customer_id: customer.id,
      email: orderData.customer_email,
      line_items: orderData.line_items,
      subtotal,
      tax,
      shipping_cost,
      total,
      shipping_address: orderData.shipping_address,
      billing_address: orderData.billing_address,
      status: 'pending',
      payment_status: 'pending'
    }
  });

  // Start order processing workflow
  await startOrderWorkflow(order.rows[0]);

  return order.rows[0];
}

// Order processing workflow
async function startOrderWorkflow(order: any) {
  await ductape.workflows.execute({
    workflow: 'process-order',
    input: {
      order_id: order.id,
      order_number: order.order_number,
      customer_email: order.email,
      total: order.total
    }
  });
}

Create Order Workflow

Create a workflow file workflows/process-order.ts:

import { Ductape } from '@ductape/sdk';

const ductape = new Ductape({
  apiKey: process.env.DUCTAPE_API_KEY!
});

export const processOrderWorkflow = {
  name: 'process-order',
  version: '1.0.0',
  steps: [
    // Step 1: Validate inventory
    {
      name: 'validate-inventory',
      type: 'function',
      handler: async (context: any) => {
        const order = await ductape.databases.findOne({
          table: 'orders',
          where: { id: context.input.order_id }
        });

        // Check inventory for all items
        for (const item of order.row.line_items) {
          const product = await ductape.databases.findOne({
            table: 'products',
            where: { id: item.product_id }
          });

          if (product.row.inventory_quantity < item.quantity) {
            throw new Error(`Insufficient inventory for ${product.row.name}`);
          }
        }

        return { valid: true };
      }
    },

    // Step 2: Create Stripe payment intent
    {
      name: 'create-payment-intent',
      type: 'action',
      action: 'stripe.create-payment-intent',
      input: {
        amount: '{{ input.total * 100 }}', // Convert to cents
        currency: 'usd',
        customer: '{{ customer.stripe_customer_id }}',
        metadata: {
          order_id: '{{ input.order_id }}',
          order_number: '{{ input.order_number }}'
        },
        receipt_email: '{{ input.customer_email }}'
      }
    },

    // Step 3: Wait for payment confirmation
    {
      name: 'wait-for-payment',
      type: 'wait',
      event: 'payment.confirmed',
      timeout: 3600 // 1 hour
    },

    // Step 4: Reserve inventory
    {
      name: 'reserve-inventory',
      type: 'function',
      handler: async (context: any) => {
        const order = await ductape.databases.findOne({
          table: 'orders',
          where: { id: context.input.order_id }
        });

        // Reduce inventory for all items
        for (const item of order.row.line_items) {
          await updateInventory(
            item.product_id,
            -item.quantity,
            'sale',
            order.row.id,
            `Order ${order.row.order_number}`
          );
        }

        // Update order status
        await ductape.databases.update({
          table: 'orders',
          where: { id: order.row.id },
          data: {
            status: 'processing',
            payment_status: 'paid',
            updated_at: new Date()
          }
        });

        return { reserved: true };
      }
    },

    // Step 5: Send order confirmation email
    {
      name: 'send-confirmation',
      type: 'notification',
      channel: 'email',
      to: '{{ input.customer_email }}',
      template: 'order-confirmation',
      data: {
        order_number: '{{ input.order_number }}',
        order_id: '{{ input.order_id }}'
      }
    },

    // Step 6: Update customer stats
    {
      name: 'update-customer-stats',
      type: 'function',
      handler: async (context: any) => {
        const order = await ductape.databases.findOne({
          table: 'orders',
          where: { id: context.input.order_id }
        });

        await ductape.databases.update({
          table: 'customers',
          where: { id: order.row.customer_id },
          data: {
            total_orders: { $increment: 1 },
            total_spent: { $increment: order.row.total },
            updated_at: new Date()
          }
        });

        return { updated: true };
      }
    },

    // Step 7: Schedule fulfillment check
    {
      name: 'schedule-fulfillment',
      type: 'job',
      schedule: '+2h', // Check in 2 hours
      handler: async (context: any) => {
        // Check if order needs fulfillment reminder
        const order = await ductape.databases.findOne({
          table: 'orders',
          where: { id: context.input.order_id }
        });

        if (order.row.fulfillment_status === 'unfulfilled') {
          // Send notification to warehouse
          await ductape.notifications.send({
            channel: 'email',
            to: 'warehouse@yourstore.com',
            template: 'fulfillment-reminder',
            data: {
              order_number: order.row.order_number,
              order_id: order.row.id
            }
          });
        }
      }
    }
  ],

  errorHandlers: [
    {
      step: 'validate-inventory',
      handler: async (context: any, error: any) => {
        // Send out of stock notification
        await ductape.notifications.send({
          channel: 'email',
          to: context.input.customer_email,
          template: 'order-failed-inventory',
          data: {
            order_number: context.input.order_number,
            reason: error.message
          }
        });

        // Update order status
        await ductape.databases.update({
          table: 'orders',
          where: { id: context.input.order_id },
          data: {
            status: 'cancelled',
            notes: error.message
          }
        });
      }
    },

    {
      step: 'wait-for-payment',
      handler: async (context: any, error: any) => {
        // Payment timeout
        await ductape.notifications.send({
          channel: 'email',
          to: context.input.customer_email,
          template: 'payment-timeout',
          data: {
            order_number: context.input.order_number
          }
        });

        await ductape.databases.update({
          table: 'orders',
          where: { id: context.input.order_id },
          data: {
            status: 'cancelled',
            notes: 'Payment timeout'
          }
        });
      }
    }
  ]
};

Stripe Webhook Handler

// Handle Stripe webhooks
app.post('/webhooks/stripe', express.raw({ type: 'application/json' }), async (req, res) => {
  const sig = req.headers['stripe-signature'] as string;

  let event;
  try {
    // Verify webhook signature
    const stripe = require('stripe')(process.env.STRIPE_SECRET_KEY);
    event = stripe.webhooks.constructEvent(
      req.body,
      sig,
      process.env.STRIPE_WEBHOOK_SECRET
    );
  } catch (err: any) {
    console.error('Webhook signature verification failed:', err.message);
    return res.status(400).send(`Webhook Error: ${err.message}`);
  }

  // Handle the event
  switch (event.type) {
    case 'payment_intent.succeeded':
      const paymentIntent = event.data.object;

      // Find order
      const order = await ductape.databases.findOne({
        table: 'orders',
        where: { stripe_payment_intent_id: paymentIntent.id }
      });

      if (order.row) {
        // Trigger workflow continuation
        await ductape.workflows.signal({
          workflow: 'process-order',
          executionId: order.row.workflow_execution_id,
          signal: 'payment.confirmed',
          data: {
            payment_intent_id: paymentIntent.id,
            amount: paymentIntent.amount
          }
        });
      }
      break;

    case 'payment_intent.payment_failed':
      const failedPayment = event.data.object;

      const failedOrder = await ductape.databases.findOne({
        table: 'orders',
        where: { stripe_payment_intent_id: failedPayment.id }
      });

      if (failedOrder.row) {
        await ductape.databases.update({
          table: 'orders',
          where: { id: failedOrder.row.id },
          data: {
            payment_status: 'failed',
            status: 'cancelled',
            notes: 'Payment failed'
          }
        });

        // Send notification
        await ductape.notifications.send({
          channel: 'email',
          to: failedOrder.row.email,
          template: 'payment-failed',
          data: {
            order_number: failedOrder.row.order_number
          }
        });
      }
      break;
  }

  res.json({ received: true });
});

Message Broker for Real-time Updates

// Publish order status updates
async function publishOrderUpdate(orderId: string, status: string) {
  await ductape.messageBrokers.publish({
    topic: 'order-updates',
    message: {
      order_id: orderId,
      status,
      timestamp: new Date().toISOString()
    }
  });
}

// Subscribe to order updates (for admin dashboard)
async function subscribeToOrderUpdates(callback: (message: any) => void) {
  await ductape.messageBrokers.subscribe({
    topic: 'order-updates',
    handler: async (message) => {
      callback(message);
    }
  });
}

Quotas and Rate Limiting

// Configure quotas for API endpoints
await ductape.quotas.configure({
  'api:create-order': {
    limit: 100,
    window: '1h',
    per: 'customer_id'
  },
  'api:search-products': {
    limit: 1000,
    window: '1h',
    per: 'ip_address'
  }
});

// Check quota before creating order
app.post('/orders', async (req, res) => {
  const customerId = req.body.customer_id;

  // Check quota
  const quotaCheck = await ductape.quotas.check({
    key: 'api:create-order',
    identifier: customerId
  });

  if (!quotaCheck.allowed) {
    return res.status(429).json({
      error: 'Rate limit exceeded',
      retryAfter: quotaCheck.retryAfter
    });
  }

  // Process order
  const order = await createOrder(req.body);

  // Increment quota
  await ductape.quotas.increment({
    key: 'api:create-order',
    identifier: customerId
  });

  res.json(order);
});

Storage for Product Images

// Upload product images
async function uploadProductImages(files: File[], productId: string): Promise<string[]> {
  const uploadPromises = files.map(file =>
    ductape.storage.upload({
      file,
      path: `products/${productId}`,
      metadata: {
        product_id: productId
      }
    })
  );

  const uploads = await Promise.all(uploadPromises);
  return uploads.map(upload => upload.url);
}

// Generate signed URL for temporary access
async function getProductImageUrl(imagePath: string): Promise<string> {
  const signedUrl = await ductape.storage.getSignedUrl({
    path: imagePath,
    expiresIn: 3600 // 1 hour
  });

  return signedUrl;
}

Automated Marketing with Jobs

// Schedule abandoned cart recovery
async function scheduleAbandonedCartEmail(cartId: string, customerEmail: string) {
  await ductape.jobs.schedule({
    name: 'abandoned-cart-recovery',
    schedule: '+24h', // Send after 24 hours
    data: {
      cart_id: cartId,
      customer_email: customerEmail
    },
    handler: async (data) => {
      // Check if cart is still abandoned
      const order = await ductape.databases.findOne({
        table: 'orders',
        where: { cart_id: data.cart_id }
      });

      if (!order.row) {
        // Send recovery email
        await ductape.notifications.send({
          channel: 'email',
          to: data.customer_email,
          template: 'abandoned-cart',
          data: {
            cart_id: data.cart_id,
            recovery_link: `https://yourstore.com/cart/${data.cart_id}`
          }
        });
      }
    }
  });
}

// Schedule post-purchase follow-up
async function scheduleFollowUpEmail(orderId: string, customerEmail: string) {
  await ductape.jobs.schedule({
    name: 'post-purchase-followup',
    schedule: '+7d', // Send 7 days after purchase
    data: {
      order_id: orderId,
      customer_email: customerEmail
    },
    handler: async (data) => {
      await ductape.notifications.send({
        channel: 'email',
        to: data.customer_email,
        template: 'review-request',
        data: {
          order_id: data.order_id
        }
      });
    }
  });
}

// Daily inventory report
await ductape.jobs.schedule({
  name: 'daily-inventory-report',
  schedule: '0 9 * * *', // Every day at 9 AM
  handler: async () => {
    // Get low stock products
    const lowStockProducts = await ductape.databases.find({
      table: 'products',
      where: {
        inventory_quantity: { $lte: 10 }
      }
    });

    if (lowStockProducts.rows.length > 0) {
      await ductape.notifications.send({
        channel: 'email',
        to: 'inventory@yourstore.com',
        template: 'daily-inventory-report',
        data: {
          low_stock_products: lowStockProducts.rows,
          date: new Date().toISOString()
        }
      });
    }
  }
});

Order Fulfillment

// Mark order as fulfilled
async function fulfillOrder(orderId: string, trackingNumber: string) {
  const order = await ductape.databases.findOne({
    table: 'orders',
    where: { id: orderId }
  });

  if (!order.row) {
    throw new Error('Order not found');
  }

  // Update order
  await ductape.databases.update({
    table: 'orders',
    where: { id: orderId },
    data: {
      status: 'fulfilled',
      fulfillment_status: 'fulfilled',
      tracking_number: trackingNumber,
      shipped_at: new Date(),
      updated_at: new Date()
    }
  });

  // Send shipping notification
  await ductape.notifications.send({
    channel: 'email',
    to: order.row.email,
    template: 'order-shipped',
    data: {
      order_number: order.row.order_number,
      tracking_number: trackingNumber,
      tracking_url: `https://tracking.com/${trackingNumber}`
    }
  });

  // Send SMS notification if customer has phone
  const customer = await ductape.databases.findOne({
    table: 'customers',
    where: { id: order.row.customer_id }
  });

  if (customer.row?.phone) {
    await ductape.notifications.send({
      channel: 'sms',
      to: customer.row.phone,
      template: 'order-shipped-sms',
      data: {
        order_number: order.row.order_number,
        tracking_number: trackingNumber
      }
    });
  }

  // Publish to message broker
  await publishOrderUpdate(orderId, 'fulfilled');

  // Schedule delivery follow-up
  await ductape.jobs.schedule({
    name: 'delivery-followup',
    schedule: '+3d', // 3 days after shipping
    data: { order_id: orderId },
    handler: async (data) => {
      await ductape.notifications.send({
        channel: 'email',
        to: order.row.email,
        template: 'delivery-confirmation',
        data: {
          order_number: order.row.order_number
        }
      });
    }
  });
}

Complete Express API

// Get products
app.get('/products', async (req, res) => {
  const { category, search, page = 1, limit = 20 } = req.query;

  const where: any = { is_active: true };

  if (category) {
    where.category = category;
  }

  if (search) {
    where.$or = [
      { name: { $regex: search, $options: 'i' } },
      { description: { $regex: search, $options: 'i' } }
    ];
  }

  const products = await ductape.databases.find({
    table: 'products',
    where,
    limit: Number(limit),
    offset: (Number(page) - 1) * Number(limit),
    orderBy: { created_at: 'desc' }
  });

  res.json(products.rows);
});

// Create order
app.post('/orders', async (req, res) => {
  try {
    const order = await createOrder(req.body);
    res.json(order);
  } catch (error: any) {
    res.status(400).json({ error: error.message });
  }
});

// Get order status
app.get('/orders/:orderNumber', async (req, res) => {
  const order = await ductape.databases.findOne({
    table: 'orders',
    where: { order_number: req.params.orderNumber }
  });

  if (!order.row) {
    return res.status(404).json({ error: 'Order not found' });
  }

  res.json(order.row);
});

// Fulfill order (admin endpoint)
app.post('/admin/orders/:orderId/fulfill', async (req, res) => {
  const { tracking_number } = req.body;

  try {
    await fulfillOrder(req.params.orderId, tracking_number);
    res.json({ success: true });
  } catch (error: any) {
    res.status(400).json({ error: error.message });
  }
});

const PORT = process.env.PORT || 3000;
app.listen(PORT, () => {
  console.log(`E-commerce API running on port ${PORT}`);
});

Next Steps

• Implement refunds and returns workflow
• Add product reviews and ratings
• Create discount codes and promotions
• Set up analytics and reporting
• Implement multi-currency support
• Add gift cards and store credit
• Create admin dashboard
• Set up monitoring and alerts

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