feat: optimize JPA performance with lazy loading and fetch joins

Signed-off-by: Mickael-7 <mickael.albuquerque@upe.br>

src/main/java/org/springframework/samples/petclinic/owner/Owner.java

@@ -61,7 +61,7 @@ public class Owner extends Person {
 	@Pattern(regexp = "\\d{10}", message = "{telephone.invalid}")
 	private String telephone;
 
-	@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
+	@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
 	@JoinColumn(name = "owner_id")
 	@OrderBy("name")
 	private final List<Pet> pets = new ArrayList<>();

src/main/java/org/springframework/samples/petclinic/owner/OwnerRepository.java

@@ -20,6 +20,7 @@ import java.util.Optional;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
 import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Query;
 
 /**
  * Repository class for <code>Owner</code> domain objects. All method names are compliant
@@ -57,6 +58,7 @@ public interface OwnerRepository extends JpaRepository<Owner, Integer> {
 	 * @throws IllegalArgumentException if the id is null (assuming null is not a valid
 	 * input for id)
 	 */
+	@Query("SELECT DISTINCT owner FROM Owner owner LEFT JOIN FETCH owner.pets p LEFT JOIN FETCH p.visits WHERE owner.id = :id")
 	Optional<Owner> findById(Integer id);
 
 }

src/main/java/org/springframework/samples/petclinic/owner/Pet.java

@@ -53,7 +53,7 @@ public class Pet extends NamedEntity {
 	@JoinColumn(name = "type_id")
 	private PetType type;
 
-	@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
+	@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
 	@JoinColumn(name = "pet_id")
 	@OrderBy("date ASC")
 	private final Set<Visit> visits = new LinkedHashSet<>();

src/main/java/org/springframework/samples/petclinic/vet/Vet.java

@@ -44,7 +44,7 @@ import jakarta.xml.bind.annotation.XmlElement;
 @Table(name = "vets")
 public class Vet extends Person {
 
-	@ManyToMany(fetch = FetchType.EAGER)
+	@ManyToMany(fetch = FetchType.LAZY)
 	@JoinTable(name = "vet_specialties", joinColumns = @JoinColumn(name = "vet_id"),
 			inverseJoinColumns = @JoinColumn(name = "specialty_id"))
 	private Set<Specialty> specialties;

src/main/java/org/springframework/samples/petclinic/vet/VetRepository.java

@@ -19,6 +19,7 @@ import org.springframework.cache.annotation.Cacheable;
 import org.springframework.dao.DataAccessException;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
+import org.springframework.data.jpa.repository.Query;
 import org.springframework.data.repository.Repository;
 import org.springframework.transaction.annotation.Transactional;
 
@@ -41,6 +42,7 @@ public interface VetRepository extends Repository<Vet, Integer> {
 	 * Retrieve all <code>Vet</code>s from the data store.
 	 * @return a <code>Collection</code> of <code>Vet</code>s
 	 */
+	@Query("SELECT DISTINCT vet FROM Vet vet LEFT JOIN FETCH vet.specialties")
 	@Transactional(readOnly = true)
 	@Cacheable("vets")
 	Collection<Vet> findAll() throws DataAccessException;
@@ -51,6 +53,7 @@ public interface VetRepository extends Repository<Vet, Integer> {
 	 * @return
 	 * @throws DataAccessException
 	 */
+	@Query("SELECT DISTINCT vet FROM Vet vet LEFT JOIN FETCH vet.specialties")
 	@Transactional(readOnly = true)
 	@Cacheable("vets")
 	Page<Vet> findAll(Pageable pageable) throws DataAccessException;