What is the N+1 query problem and how do you solve it in Spring Data JPA? N+1 क्वेरी समस्या क्या है और स्प्रिंग डेटा JPA में इसे कैसे हल करें?

The N+1 problem occurs when fetching a list of N parent entities triggers 1 query for the parents plus N additional queries, one per parent, to lazily load each one's related collection or association — resulting in N+1 total queries instead of one efficient join.

It's solved by fetching related data eagerly in a single query using JOIN FETCH in a JPQL query, an @EntityGraph on the repository method to specify which associations to load together, or by batching lazy fetches with @BatchSize to reduce the number of round-trips.

@Query("SELECT a FROM Author a JOIN FETCH a.books")
List<Author> findAllWithBooks();

@EntityGraph(attributePaths = "books")
List<Author> findAll();