Queries: JPQL, Native, Derived, Criteria

Spring Data JPA offers derived methods (name-parsed queries), JPQL @Query (entity-based), native SQL @Query (raw SQL), and @Modifying (bulk UPDATE/DELETE) – start with derived, escalate to @Query when needed.

@QueryHints passes per-query optimization hints to Hibernate – readOnly skips dirty checking for that query, cacheable uses L2 cache, fetchSize controls JDBC batching, timeout cancels slow queries.

Derived methods for simple queries, JPQL for custom object queries, native SQL for database-specific needs, and @Modifying for bulk update/delete.

@QueryHints fine-tune a single query (readOnly, cacheable, fetchSize, timeout); @Transactional(readOnly) sets the policy for the whole transaction.

@NamedQuery defines a reusable, startup-validated JPQL query on an entity; @NamedNativeQuery does the same for raw SQL; both are pre-compiled and fail fast if the query is broken.

The Criteria API builds queries as type-safe object trees for dynamic filters; Specification<T> is a composable Spring Data wrapper that combines predicates with and/or -- no string concatenation needed.