Event Sourcing

Event Sourcing Overview

At its core, event sourcing is about doing one thing well inside your DynamoDB project. Once you understand the pattern, you can apply it consistently across features and teams.

Good event sourcing pays off across the whole codebase: fewer surprises, easier testing, and smoother onboarding. The snippet below is a solid starting point.

import { DynamoDBClient } from '@aws-sdk/client-dynamodb';
import { DynamoDBDocumentClient, GetCommand, PutCommand } from '@aws-sdk/lib-dynamodb';

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

// reuse docClient across the module for efficient, typed access
await docClient.send(new PutCommand({ TableName: 'Orders', Item: { pk: '1' } }));

The DynamoDBDocumentClient maps plain JavaScript objects to DynamoDB item format for you.

Event Sourcing Example

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

const docClient = DynamoDBDocumentClient.from(new DynamoDBClient({}));
// docClient.send(new PutCommand(...)) etc.

• Start from a minimal Event Sourcing example and grow it only as needed.
• Keep configuration explicit so Event Sourcing behaves the same in every environment.
• Name things clearly so teammates understand your Event Sourcing at a glance.
• Add tests around Event Sourcing early to lock in expected behaviour.

Amazon DynamoDB Cheatsheet

Handy DynamoDB (AWS SDK v3) reference related to event sourcing.

How Event Sourcing Works in DynamoDB

Event Sourcing builds on DynamoDB's key-value and document model, where every item lives in a partition chosen by its partition key and is optionally ordered by a sort key.

The DynamoDBDocumentClient maps plain JavaScript objects to DynamoDB item format for you.

• Design access patterns first, then model keys around them.
• Prefer Query over Scan for predictable performance.
• Use expressions to read and write only what you need.
• Keep items small and avoid hot partitions.

Practical Guidance for Event Sourcing

In production, event sourcing should be cost-aware and resilient. Right-size capacity, handle throttling with retries, and lean on indexes to support your query patterns.

Common Mistakes

• Copying event sourcing snippets without understanding what each line does.
• Skipping error handling and edge cases when wiring up event sourcing.
• Leaving event sourcing untested, so regressions slip into production.
• Over-engineering event sourcing before you actually need the extra flexibility.

Key Takeaways

• Event Sourcing is a core part of working effectively with DynamoDB.
• Start small and keep event sourcing focused on a single responsibility.
• Apply consistent patterns so event sourcing scales across your project.
• Test and document event sourcing to keep it maintainable over time.