Aws Dynamodb

AWS DynamoDB Skill

DynamoDB is a fully managed NoSQL database designed for single-digit millisecond performance at any scale. Master single-table design and access pattern modeling.

Sources: DynamoDB Docs | SDK v3 | Best Practices

Core Principle

Design for access patterns, not entities. Think access-pattern-first.

DynamoDB requires you to know your queries before designing your schema. Model around how you'll access data, not how data relates. Single-table design stores multiple entity types in one table using generic key attributes.

Key Concepts

Single-Table Design

Why Single Table?

• Fetch related data in single query
• Reduce round trips and costs
• Enable transactions across entity types
• Simplify operations (backup, restore, IAM)

Generic Key Pattern

// Instead of entity-specific keys:
// userId, orderId, productId

// Use generic keys that work for all entities:
interface BaseItem {
  PK: string;   // Partition Key
  SK: string;   // Sort Key
  GSI1PK?: string;  // First GSI partition key
  GSI1SK?: string;  // First GSI sort key
  EntityType: string;
  // ... entity-specific attributes
}

Example: E-commerce Schema

// Users
{ PK: 'USER#123', SK: 'PROFILE', EntityType: 'User', name: 'John', email: 'john@test.com' }
{ PK: 'USER#123', SK: 'ADDRESS#1', EntityType: 'Address', street: '123 Main', city: 'NYC' }

// Orders for user (1:N relationship)
{ PK: 'USER#123', SK: 'ORDER#2024-001', EntityType: 'Order', total: 99.99, status: 'shipped' }
{ PK: 'USER#123', SK: 'ORDER#2024-002', EntityType: 'Order', total: 49.99, status: 'pending' }

// Order details (query by order ID using GSI)
{ PK: 'USER#123', SK: 'ORDER#2024-001', GSI1PK: 'ORDER#2024-001', GSI1SK: 'ORDER', ... }
{ PK: 'ORDER#2024-001', SK: 'ITEM#1', GSI1PK: 'ORDER#2024-001', GSI1SK: 'ITEM#1', productId: 'PROD#456', qty: 2 }

// Products
{ PK: 'PROD#456', SK: 'PRODUCT', EntityType: 'Product', name: 'Widget', price: 29.99 }

Access Patterns Covered

1. Get user profile          → Query PK='USER#123', SK='PROFILE'
2. Get user with addresses   → Query PK='USER#123', SK begins_with 'ADDRESS'
3. Get all user orders       → Query PK='USER#123', SK begins_with 'ORDER'
4. Get order by ID           → Query GSI1, PK='ORDER#2024-001'
5. Get order with items      → Query GSI1, PK='ORDER#2024-001'
6. Get product details       → Query PK='PROD#456', SK='PRODUCT'

SDK v3 Setup (TypeScript)

Install Dependencies

npm install @aws-sdk/client-dynamodb @aws-sdk/lib-dynamodb

Client Configuration

// lib/dynamodb.ts
import { DynamoDBClient } from '@aws-sdk/client-dynamodb';
import { DynamoDBDocumentClient } from '@aws-sdk/lib-dynamodb';

const client = new DynamoDBClient({
  region: process.env.AWS_REGION || 'us-east-1',
  // For local development with DynamoDB Local
  ...(process.env.DYNAMODB_LOCAL && {
    endpoint: 'http://localhost:8000',
    credentials: { accessKeyId: 'local', secretAccessKey: 'local' }
  })
});

// Document client for simplified operations
export const docClient = DynamoDBDocumentClient.from(client, {
  marshallOptions: {
    removeUndefinedValues: true,  // Important: match v2 behavior
    convertClassInstanceToMap: true
  },
  unmarshallOptions: {
    wrapNumbers: false
  }
});

export const TABLE_NAME = process.env.DYNAMODB_TABLE || 'MyTable';

Type Definitions

// types/dynamodb.ts
export interface BaseItem {
  PK: string;
  SK: string;
  GSI1PK?: string;
  GSI1SK?: string;
  EntityType: string;
  createdAt: string;
  updatedAt: string;
}

export interface User extends BaseItem {
  EntityType: 'User';
  userId: string;
  email: string;
  name: string;
}

export interface Order extends BaseItem {
  EntityType: 'Order';
  orderId: string;
  userId: string;
  total: number;
  status: 'pending' | 'paid' | 'shipped' | 'delivered';
}

// Key builders
export const keys = {
  user: (userId: string) => ({
    PK: `USER#${userId}`,
    SK: 'PROFILE'
  }),
  userOrders: (userId: string) => ({
    PK: `USER#${userId}`,
    SKPrefix: 'ORDER#'
  }),
  order: (userId: string, orderId: string) => ({
    PK: `USER#${userId}`,
    SK: `ORDER#${orderId}`,
    GSI1PK: `ORDER#${orderId}`,
    GSI1SK: 'ORDER'
  })
};

CRUD Operations

Put Item (Create/Update)

import { PutCommand } from '@aws-sdk/lib-dynamodb';
import { docClient, TABLE_NAME } from './dynamodb';
import { User, keys } from './types';

async function createUser(userId: string, data: { email: string; name: string }): Promise<User> {
  const now = new Date().toISOString();
  const item: User = {
    ...keys.user(userId),
    EntityType: 'User',
    userId,
    email: data.email,
    name: data.name,
    createdAt: now,
    updatedAt: now
  };

  await docClient.send(new PutCommand({
    TableName: TABLE_NAME,
    Item: item,
    ConditionExpression: 'attribute_not_exists(PK)'  // Prevent overwrite
  }));

  return item;
}

Get Item (Read)

import { GetCommand } from '@aws-sdk/lib-dynamodb';

async function getUser(userId: string): Promise<User | null> {
  const result = await docClient.send(new GetCommand({
    TableName: TABLE_NAME,
    Key: keys.user(userId)
  }));

  return (result.Item as User) || null;
}

Query (List/Search)

import { QueryCommand } from '@aws-sdk/lib-dynamodb';

// Get all orders for a user
async function getUserOrders(userId: string): Promise<Order[]> {
  const result = await docClient.send(new QueryCommand({
    TableName: TABLE_NAME,
    KeyConditionExpression: 'PK = :pk AND begins_with(SK, :sk)',
    ExpressionAttributeValues: {
      ':pk': `USER#${userId}`,
      ':sk': 'ORDER#'
    },
    ScanIndexForward: false  // Newest first
  }));

  return (result.Items as Order[]) || [];
}

// Query GSI by order ID
async function getOrderById(orderId: string): Promise<Order | null> {
  const result = await docClient.send(new QueryCommand({
    TableName: TABLE_NAME,
    IndexName: 'GSI1',
    KeyConditionExpression: 'GSI1PK = :pk',
    ExpressionAttributeValues: {
      ':pk': `ORDER#${orderId}`
    }
  }));

  return (result.Items?.[0] as Order) || null;
}

// Paginated query
async function getUserOrdersPaginated(
  userId: string,
  pageSize: number = 20,
  lastKey?: Record<string, any>
): Promise<{ items: Order[]; lastKey?: Record<string, any> }> {
  const result = await docClient.send(new QueryCommand({
    TableName: TABLE_NAME,
    KeyConditionExpression: 'PK = :pk AND begins_with(SK, :sk)',
    ExpressionAttributeValues: {
      ':pk': `USER#${userId}`,
      ':sk': 'ORDER#'
    },
    Limit: pageSize,
    ExclusiveStartKey: lastKey
  }));

  return {
    items: (result.Items as Order[]) || [],
    lastKey: result.LastEvaluatedKey
  };
}

Update Item

import { UpdateCommand } from '@aws-sdk/lib-dynamodb';

async function updateUser(userId: string, updates: Partial<Pick<User, 'name' | 'email'>>): Promise<User> {
  // Build update expression dynamically
  const updateParts: string[] = ['#updatedAt = :updatedAt'];
  const names: Record<string, string> = { '#updatedAt': 'updatedAt' };
  const values: Record<string, any> = { ':updatedAt': new Date().toISOString() };

  if (updates.name !== undefined) {