What is the N+1 problem in Hibernate and how to solve it?

The N+1 problem in Hibernate occurs when, during the loading of a collection of entities, one query is executed for the main entity and an additional N queries for related entities, which significantly reduces performance.

For example, when loading a list of users and their roles, Hibernate might execute 1 query for users and one query for each user's roles.

Solutions:

• Use fetch join in JPQL/HQL to load related entities with a single query:

  SELECT u FROM User u JOIN FETCH u.roles
  

• Configure fetch = FetchType.EAGER for necessary associations (with caution to avoid loading unnecessary data).
• Use EntityGraph to specify which associations to load immediately.

This reduces the number of database queries and improves application performance.