Hibernate Basics

Introduction

Hibernate is the default JPA provider Spring Boot ships with. It handles the entity ↔ row mapping, lazy loading, dirty checking and 1L caching for you. Knowing how it works prevents 90% of mysterious N+1 bugs.

Understanding the topic

The mental model:

• Persistence Context — a per-transaction map of managed entities.
• Dirty checking — Hibernate compares snapshots and auto-issues UPDATE on commit.
• Lazy loading — relations fetched only when accessed (requires open session).
• First-level cache — same entity within a TX = same Java instance.

Best practices

• Always use FetchType.LAZY on @OneToMany/@ManyToMany — defaults bite.
• Avoid @Transactional(readOnly=false) for queries — set readOnly=true for read endpoints.
• Disable open-in-view in production: spring.jpa.open-in-view: false.