Event Sourcing - Complete Guide

Storing Application State as a Sequence of Events

Event Sourcing is a pattern where application state is stored as a sequence of events rather than current state. Instead of updating records, events are appended to an event store.

This provides an audit trail, enables time travel, and allows reconstructing any state by replaying events. This guide covers the fundamentals, implementation patterns, and best practices for event sourcing.

this.timestamp = timestamp;

this.type = 'OrderCreated';

constructor(events = []) {

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async saveEvents(aggregateId, events, expectedVersion) {

// Optimistic concurrency check

const currentVersion = await this.getVersion(aggregateId);

Frequently asked questions

What is Event Sourcing?

Event Sourcing is a pattern where application state is stored as a sequence of events rather than current state.

Frequently Asked Questions (FAQ)?

Frequently Asked Questions (FAQ)

When should I use Event Sourcing??

When should I use Event Sourcing?

Use Event Sourcing when: you need comple?

Use Event Sourcing when: you need complete audit trail, need to reconstruct past states, have complex business rules requiring history, need event replay capabilities, or building event-driven systems. Good for: financial systems, order management, collaboration tools, or any domain where "what happened" is as important as current state.

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