Fix N+1 Query Performance Issue in /vets.html Endpoint

[shaykeren]

Problem

Critical N+1 query performance issue detected in the /vets.html endpoint causing 5 repeated database queries per request.

Issue ID: e8efc2b4-5f5e-11f0-bbd9-0242ac160009
Affected Endpoint: HTTP GET /vets.html
Service: spring-petclinic
Trace ID: E78ADC1B4AB172AAA6DAC2D716CB4E0D

Solution

Implemented eager fetching with JOIN FETCH to resolve the N+1 query pattern by:

1. VetRepository Changes

• Added findAllWithSpecialties() method with @Query("SELECT v FROM Vet v LEFT JOIN FETCH v.specialties")
• Added paginated version findAllWithSpecialties(Pageable pageable) for the HTML endpoint
• Both methods use @Transactional(readOnly = true) and @Cacheable("vets") to maintain existing behavior

2. VetController Changes

• Updated findPaginated() method to use findAllWithSpecialties(pageable) instead of findAll(pageable)
• Updated showResourcesVetList() method to use findAllWithSpecialties() instead of findAll()

Impact

• Resolves N+1 query issue by fetching vets and their specialties in a single query
• Maintains existing functionality including pagination and caching
• Preserves all existing method signatures and behavior
• Minimal code changes focused only on the specific performance issue

Testing

The changes maintain backward compatibility and preserve all existing functionality while optimizing database queries.