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

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

@@ -13,11 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.springframework.samples.petclinic.vet;
-
-import java.util.List;
-
-import org.springframework.data.domain.Page;
+package org.springframework.samples.petclinic.vet;import java.util.List;import org.springframework.data.domain.Page;
 import org.springframework.data.domain.PageRequest;
 import org.springframework.data.domain.Pageable;
 import org.springframework.stereotype.Controller;
@@ -32,16 +28,13 @@
  * @author Ken Krebs
  * @author Arjen Poutsma
  */
-@Controller
-class VetController {
+@Controllerclass VetController {
 
 	private final VetRepository vetRepository;
 
 	public VetController(VetRepository clinicService) {
 		this.vetRepository = clinicService;
-	}
-
-	@GetMapping("/vets.html")
+	}@GetMapping("/vets.html")
 	public String showVetList(@RequestParam(defaultValue = "1") int page, Model model) {
 		// Here we are returning an object of type 'Vets' rather than a collection of Vet
 		// objects so it is simpler for Object-Xml mapping
@@ -58,21 +51,17 @@ private String addPaginationModel(int page, Page<Vet> paginated, Model model) {
 		model.addAttribute("totalItems", paginated.getTotalElements());
 		model.addAttribute("listVets", listVets);
 		return "vets/vetList";
-	}
-
-	private Page<Vet> findPaginated(int page) {
+	}private Page<Vet> findPaginated(int page) {
 		int pageSize = 5;
 		Pageable pageable = PageRequest.of(page - 1, pageSize);
-		return vetRepository.findAll(pageable);
-	}
-
-	@GetMapping({ "/vets" })
+		return vetRepository.findAllWithSpecialties(pageable);
+	}@GetMapping({ "/vets" })
 	public @ResponseBody Vets showResourcesVetList() {
 		// Here we are returning an object of type 'Vets' rather than a collection of Vet
 		// objects so it is simpler for JSon/Object mapping
 		Vets vets = new Vets();
-		vets.getVetList().addAll(this.vetRepository.findAll());
+		vets.getVetList().addAll(this.vetRepository.findAllWithSpecialties());
 		return vets;
 	}
 
-}
+}

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

@@ -13,16 +13,13 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.springframework.samples.petclinic.vet;
-
-import org.springframework.cache.annotation.Cacheable;
+package org.springframework.samples.petclinic.vet;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;
-
-import java.util.Collection;
+import org.springframework.transaction.annotation.Transactional;import java.util.Collection;
 
 /**
  * Repository class for <code>Vet</code> domain objects All method names are compliant
@@ -34,8 +31,7 @@
  * @author Juergen Hoeller
  * @author Sam Brannen
  * @author Michael Isvy
- */
-public interface VetRepository extends Repository<Vet, Integer> {
+ */import org.springframework.data.jpa.repository.Query;public interface VetRepository extends Repository<Vet, Integer> {
 
 	/**
 	 * Retrieve all <code>Vet</code>s from the data store.
@@ -55,4 +51,14 @@ public interface VetRepository extends Repository<Vet, Integer> {
 	@Cacheable("vets")
 	Page<Vet> findAll(Pageable pageable) throws DataAccessException;
 
-}
+	@Query("SELECT v FROM Vet v LEFT JOIN FETCH v.specialties")
+	@Transactional(readOnly = true)
+	@Cacheable("vets")
+	List<Vet> findAllWithSpecialties() throws DataAccessException;
+
+	@Query("SELECT v FROM Vet v LEFT JOIN FETCH v.specialties")
+	@Transactional(readOnly = true)
+	@Cacheable("vets")
+	Page<Vet> findAllWithSpecialties(Pageable pageable) throws DataAccessException;
+
+}