Grokking Spring Boot
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Spring Data Repositories

How can a method with no body run a database query?

The booking service declares SeatRepository as an interface. Nobody in the project writes a class that implements it. Yet a service that calls seats.findByEventIdAndLabel(eventId, "A12") receives seat A12. The log shows a correct SQL query with both conditions.

public interface SeatRepository extends JpaRepository<Seat, Long> {

    Optional<Seat> findByEventIdAndLabel(Long eventId, String label);

    long countByEventId(Long eventId);

    @Query("""
            select s from Seat s
            where s.event

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