Explain the N+1 Query Problem and how to fix it.

What is it?

Occurs when you fetch a list of N objects, and for each object, a separate query is executed to fetch a related detail (e.g., fetching 10 Orders and then 10 separate queries for each Order's Customer).

How to Fix:

1. Join Fetch: Use JOIN FETCH in JPQL (SELECT o FROM Order o JOIN FETCH o.customer).
2. Entity Graph: Use @EntityGraph to define which attributes should be fetched eagerly for a specific query.
3. Batch Size: Use @BatchSize to fetch related entities in larger chunks.