DVD Rental — SWI-Prolog Web App (generated-app style)

A complete DVD rental management system built with SWI-Prolog. The app follows a generated-app layout: domain logic in Prolog, HTTP/HTML in the server, and durable data in PostgreSQL.

Architecture

Layer	Role
domain.pl	Logic, rules, and “query layer” over facts (films, customers, rentals, rent/return)
server.pl	HTTP server, HTML rendering, routing
db.pl	Persistence: load/save facts between Prolog and PostgreSQL (via psql)
PostgreSQL	Durable tables: languages, categories, actors, films, film_actors, film_categories, customers, inventory, rentals

Data is loaded from Postgres at startup via db:db_load; mutations (rent/return) are persisted with db:db_persist_rental and db:db_persist_return.

Requirements

• SWI-Prolog 8.0+
• PostgreSQL (client + server for persistence)
• Devbox (recommended: pins Prolog and Postgres)

Running with Devbox (recommended)

Devbox provides SWI-Prolog and PostgreSQL so all dependencies run locally.

1. One-time: initialize Postgres and the database

cd prolog-dev-rental
devbox shell
initdb                    # once: create PGDATA
devbox services up -b     # start PostgreSQL in background (or: devbox services up postgresql)
exit
devbox run init-db        # create DB 'dvdrental' and load schema + seed data

2. Start the app

devbox run start

The server listens on http://localhost:8080/.

To run with a shell (e.g. to run swipl or psql):

devbox shell
devbox services up -b     # if Postgres not already running
swipl server.pl           # or use the REPL

Environment (optional)

The app reads PostgreSQL connection from the environment (defaults in parentheses):

• PGHOST (localhost; with Devbox Postgres plugin often ./.devbox/virtenv/postgresql)
• PGPORT (5432)
• PGUSER (empty)
• PGDATABASE (dvdrental)

No need to set these if you use Devbox’s default Postgres setup.

Running without Devbox

1. Install SWI-Prolog and PostgreSQL.

2. Create and initialize the database:

   createdb dvdrental
   psql -d dvdrental -f schema.sql

3. Start the server:

   swipl server.pl

Set PGHOST, PGPORT, PGUSER, PGDATABASE if your Postgres is not on localhost:5432 with database dvdrental.

Project structure

domain.pl       Domain logic: dynamic facts, queries, rent/return commands
server.pl       Web layer: HTTP server, routing, HTML
db.pl           Persistence: db_load, db_persist_rental, db_persist_return (psql)
schema.sql      PostgreSQL schema and seed data
scripts/        init-db.sh — create DB and load schema (devbox run init-db)
static/         style.css

Features

• Browse and search the film catalog
• Filter films by category
• Film detail pages with cast, availability, and rent form
• Customer directory with rental history
• Rent films (with availability checks) and return them
• Dashboard with live stats (films, customers, active rentals)

All data is stored in PostgreSQL; the app loads it at startup and persists new rentals and returns.