Tutorial: Trading Demo

Mon, 01 Jan 0001 00:00:00 +0000

The trading demo is a self-contained desktop app that embeds @drasi/lib and renders live query results in its own window — no browser, no HTTP/SSE, no REST, no Python. It’s a faithful port of drasi-server’s examples/trading demo, and it’s the best way to see every concept in this documentation working together.

The full source is in examples/trading.

What it demonstrates

Real PostgreSQL CDC — reference data (stocks, portfolio, watchlist) lives in a real Postgres database and is streamed into the engine via Drasi’s Postgres source (logical replication) plus a Postgres bootstrap snapshot.
Synthetic joins — HAS_PRICE, OWNS_STOCK, and ON_WATCHLIST relate elements across sources (and across a database and a live feed) with no foreign keys, entirely inside the query. See Concepts → Synthetic joins.
In-process price feed — a tiny Node random-walk generator pushes stock_prices into a JavaScript source.
Application reactions — one addJsReaction per query streams result diffs straight to the renderer over a single IPC channel; the dashboard merges ADD/UPDATE/DELETE/aggregation diffs into live tables.
Plugins downloaded at runtime — the Postgres source and bootstrap plugins are pulled from ghcr.io/drasi-project on first launch and cached locally. Nothing is baked in. See Working with plugins.

Architecture

flowchart LR
 subgraph pg[PostgreSQL - Docker]
 T1[stocks]
 T2[portfolio]
 T3[watchlist]
 end
 subgraph main[Electron main - embeds @drasi/lib]
 PS[postgres source<br/>downloaded OCI]
 PF[price-feed<br/>JS source]
 Q[5 continuous queries<br/>+ synthetic joins]
 RX[addJsReaction]
 end
 R[Electron renderer<br/>React dashboard]

 pg -->|logical replication + bootstrap| PS
 PS --> Q
 PF -->|pushChange| Q
 Q --> RX
 RX -->|IPC: trading:stream| R

The native addon is N-API v9 (ABI-stable), so it loads directly in Electron’s main process with no electron-rebuild.

Examples on @drasi/lib Docs

Tutorial: Trading Demo

What it demonstrates

Architecture