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DCB Event Sourced

Implementation of the Dynamic Consistency Boundary (DCB) pattern for Node.js/TypeScript, based on Sara Pellegrini's design.

Project Structure

Monorepo managed with Lerna and Yarn workspaces.

Packages

packages/event-store (@dcb-es/event-store) — Core event store abstractions, in-memory implementation, event handling (decision models, tag matching)
packages/event-store-postgres (@dcb-es/event-store-postgres) — Postgres implementation using pg, tests use testcontainers

Examples

examples/course-manager-cli — Simple CLI example (Course/Students domain)
examples/course-manager-cli-with-readmodel — Extended example with read models

Shared Test Infrastructure

test/vitest.globalSetup.ts — Starts/stops a testcontainers Postgres instance, shares connection URI via process.env.__PG_CONNECTION_URI
test/testPgDbPool.ts — Creates isolated test databases per test suite; imported via @test Vite resolve alias

Commands

npm test — Run all tests via Lerna (each package uses vitest run)
npm run build — Build all packages (must build before running dependent package tests)
npm run lint / npm run lint-fix — ESLint across all packages
Per-package: cd packages/<name> && npm test

Tech Stack

TypeScript, Vitest, ESLint + Prettier
Postgres tests require Docker (testcontainers)
Dependencies: luxon (dates), uuid, pg

Key Concepts

EventStore: Interface for querying and appending events with optimistic concurrency
Tags: Key-value pairs on events used for filtering/querying
Query: Defines which events to fetch (by event types and tag filters)
Decision Model (buildDecisionModel): Builds state from events for command validation
Event Handlers: Projections/process managers that react to events
SequencePosition: Global ordering of events, used for concurrency checks