Glossary

ORM

ORM (Object-Relational Mapping) is a layer between your code and the database that lets you work with tables as objects. Instead of writing SQL queries, you work with classes and methods, and the ORM generates SQL for you.

Benefits and cost

ORM speeds up development, protects against SQL injection, and makes it easy to switch databases. The cost: overhead and the risk of inefficient queries. The classic example is the N+1 problem, where ORM fires a separate query per record instead of one JOIN.

Two patterns

Active Record — the model knows how to save itself. Code looks like $user->save(). Simpler, but tightly couples the model to persistence
Data Mapper — the model and persistence logic are separated into a dedicated class (Repository/Mapper). More complex, but more flexible for large projects