Library Loans Explorer
Flask front end over a relational library database: a member's full loan history and live copy availability by branch, on PostgreSQL or SQLite.
Overview
A small web app over a five-table library schema (members, books, branches, book copies and loans), built for Problem Set 3 of NYU Tandon's CS-GY 6083 Principles of Database Systems in Spring 2025. A loan's key is member, copy and loan date, so the same member can borrow the same copy again later, and a copy is available when it has no loan without a return date.
By the numbers
- 2 database backends
- parameterized SQL
- pytest on both
Highlights
- 01
Built for NYU's Principles of Database Systems (Spring 2025): a member enters an ID and sees every loan they have made, then clicks a book to see which copies are on the shelf right now and at which branch.
- 02
One codebase runs on PostgreSQL through a psycopg2 connection pool or on SQLite with no setup, chosen by one DATABASE_URL setting; one command creates the schema and loads the sample data on either.
- 03
Every query is parameterized, bad input gets a 400 or 404, database errors are logged but not shown to users, and a pytest suite runs on SQLite by default and on PostgreSQL when pointed at one.
The story
A small web app over a five-table library schema (members, books, branches, book copies and loans), built for Problem Set 3 of NYU Tandon’s CS-GY 6083 Principles of Database Systems in Spring 2025. A loan’s key is member, copy and loan date, so the same member can borrow the same copy again later, and a copy is available when it has no loan without a return date.
It was written against PostgreSQL and later made to run on SQLite as well, so it can be tried straight from a fresh clone: flask --app app init-db loads the sample data (5 members, 5 branches, 8 books, 36 copies, 20 loans) on either backend.