Category Archives: Без рубрики

There is one of the most common (and subtle) pitfalls of Spring’s @Transactional: self-invocation, which can silently break transactional (and other proxy-based) behavior. 🔎 What is self-invocation? It’s when a method in a Spring bean calls another method on the … Continue reading →

✅ When you call a @Transactional method from another @Transactional method in the same bean (or same Spring proxy): By default, Spring uses propagation REQUIRED, which means: The inner @Transactional method joins the existing transaction of the outer method. There’s … Continue reading →

let’s put it all together with two clean, full examples side by side: one where batch fetching works (correct) and one where it doesn’t work (incorrect). I’ll give you them both without extra comments, so you can clearly compare. ✅ … Continue reading →

when I say “proxies,” I do mean entities, but specifically lazy-loaded entities or collections that Hibernate wraps in a proxy object. Here’s what that means: 🔎 What is a proxy in Hibernate? A proxy is a lightweight placeholder object Hibernate … Continue reading →

✅ What happens when you load an entity? When you fetch an entity with Hibernate (e.g., em.find() or HQL query), the lookup happens in order: 1️⃣ First-level cache (1st-level) — also called the persistence context or session cache: Every open … Continue reading →

🚫 1. Detached entities or closed session Batch fetching works only if multiple lazy proxies are accessed within the same persistence context (i.e., the same open Hibernate Session or JPA EntityManager). If you load entities in one transaction but access … Continue reading →

batch fetching is a great way to avoid the N+1 problem without forcing eager loading. Let’s break it down clearly: 🔎 What is batch fetching? When you use lazy loading, Hibernate loads collections or associated entities on demand — but … Continue reading →

You configure the fetch type for an association directly on your entity mapping using the fetch attribute of @OneToOne, @OneToMany, @ManyToOne, or @ManyToMany. Here’s how: ✅ For @OneToOne and @ManyToOne By default, these are EAGER, but you can override: ✅ … Continue reading →

🔎 The root cause: how SQL JOINs work with one-to-many Imagine you have: Author (id=1) with 3 Books (Book A, Book B, Book C). When you do a JOIN to get authors and their books: Your SQL result will look … Continue reading →

✅ 1. Use JOIN FETCH in JPQL/HQL This is the most direct way: This forces Hibernate to fetch authors and their books in one SQL query. ✅ 2. Use EntityGraph (JPA 2.1+) If you want to avoid hard-coding fetch joins … Continue reading →