Switch owner-related associations to LAZY and restore MVC rendering via OSIV

Signed-off-by: Mohit Kumar <mohitkmeena2001@gmail.com>

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/OwnerController.java

@@ -62,7 +62,7 @@ class OwnerController {
 	@ModelAttribute("owner")
 	public Owner findOwner(@PathVariable(name = "ownerId", required = false) Integer ownerId) {
 		return ownerId == null ? new Owner()
-				: this.owners.findById(ownerId)
+				: this.owners.findByIdWithPets(ownerId)
 					.orElseThrow(() -> new IllegalArgumentException("Owner not found with id: " + ownerId
 							+ ". Please ensure the ID is correct " + "and the owner exists in the database."));
 	}
@@ -89,6 +89,15 @@ class OwnerController {
 		return "owners/findOwners";
 	}
 
+	/**
+	 * Optimized owner search using DTO projection to avoid N+1 queries. This method now
+	 * executes only 2 queries total: 1. A single query with GROUP_CONCAT to fetch all
+	 * owner data with aggregated pet names 2. A count query for pagination
+	 * <p>
+	 * Previously, this executed 1 + N + M queries where N = number of owners and M =
+	 * total number of pets.
+	 * </p>
+	 */
 	@GetMapping("/owners")
 	public String processFindForm(@RequestParam(defaultValue = "1") int page, Owner owner, BindingResult result,
 			Model model) {
@@ -98,8 +107,8 @@ class OwnerController {
 			lastName = ""; // empty string signifies broadest possible search
 		}
 
-		// find owners by last name
-		Page<Owner> ownersResults = findPaginatedForOwnersLastName(page, lastName);
+		// find owners by last name using optimized DTO projection
+		Page<OwnerSearchResult> ownersResults = findPaginatedForOwnersLastName(page, lastName);
 		if (ownersResults.isEmpty()) {
 			// no owners found
 			result.rejectValue("lastName", "notFound", "not found");
@@ -107,17 +116,17 @@ class OwnerController {
 		}
 
 		if (ownersResults.getTotalElements() == 1) {
-			// 1 owner found
-			owner = ownersResults.iterator().next();
-			return "redirect:/owners/" + owner.getId();
+			// 1 owner found - redirect to detail view
+			OwnerSearchResult ownerResult = ownersResults.iterator().next();
+			return "redirect:/owners/" + ownerResult.getId();
 		}
 
 		// multiple owners found
 		return addPaginationModel(page, model, ownersResults);
 	}
 
-	private String addPaginationModel(int page, Model model, Page<Owner> paginated) {
-		List<Owner> listOwners = paginated.getContent();
+	private String addPaginationModel(int page, Model model, Page<OwnerSearchResult> paginated) {
+		List<OwnerSearchResult> listOwners = paginated.getContent();
 		model.addAttribute("currentPage", page);
 		model.addAttribute("totalPages", paginated.getTotalPages());
 		model.addAttribute("totalItems", paginated.getTotalElements());
@@ -125,10 +134,10 @@ class OwnerController {
 		return "owners/ownersList";
 	}
 
-	private Page<Owner> findPaginatedForOwnersLastName(int page, String lastname) {
+	private Page<OwnerSearchResult> findPaginatedForOwnersLastName(int page, String lastname) {
 		int pageSize = 5;
 		Pageable pageable = PageRequest.of(page - 1, pageSize);
-		return owners.findByLastNameStartingWith(lastname, pageable);
+		return owners.findOwnerSearchResultsByLastName(lastname, pageable);
 	}
 
 	@GetMapping("/owners/{ownerId}/edit")
@@ -137,6 +146,7 @@ class OwnerController {
 	}
 
 	@PostMapping("/owners/{ownerId}/edit")
+	@Transactional
 	public String processUpdateOwnerForm(@Valid Owner owner, BindingResult result, @PathVariable("ownerId") int ownerId,
 			RedirectAttributes redirectAttributes) {
 		if (result.hasErrors()) {
@@ -157,27 +167,36 @@ class OwnerController {
 	}
 
 	/**
-	 * Custom handler for displaying an owner.
+	 * Custom handler for displaying an owner. Uses EntityGraph to efficiently load pets
+	 * and visits in a single query.
 	 * @param ownerId the ID of the owner to display
 	 * @return a ModelMap with the model attributes for the view
 	 */
 	@GetMapping("/owners/{ownerId}.html")
 	public ModelAndView showOwner(@PathVariable("ownerId") int ownerId) {
 		ModelAndView mav = new ModelAndView("owners/ownerDetails");
-		Optional<Owner> optionalOwner = this.owners.findById(ownerId);
+		// Use EntityGraph to load owner with pets and visits in one query
+		Optional<Owner> optionalOwner = this.owners.findByIdWithPetsAndVisits(ownerId);
 		Owner owner = optionalOwner.orElseThrow(() -> new IllegalArgumentException(
 				"Owner not found with id: " + ownerId + ". Please ensure the ID is correct "));
 		mav.addObject(owner);
 		return mav;
 	}
 
+	/**
+	 * REST endpoint for owner resource. Uses EntityGraph to efficiently load all related
+	 * data in a single query instead of relying on manual initialization.
+	 */
 	@GetMapping("/owners/{ownerId}")
 	@ResponseBody
 	@Transactional(readOnly = true)
 	public Owner showOwnerResource(@PathVariable("ownerId") int ownerId) {
-
-		return this.owners.findById(ownerId)
+		// Use EntityGraph to load owner with all related data efficiently
+		Owner owner = this.owners.findByIdWithPetsAndVisits(ownerId)
 			.orElseThrow(() -> new IllegalArgumentException("Owner not found with id: " + ownerId));
+
+		// No need for manual initialization - EntityGraph already loaded everything
+		return owner;
 	}
 
 }

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

@@ -19,7 +19,10 @@ import java.util.Optional;
 
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
+import org.springframework.data.jpa.repository.EntityGraph;
 import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Query;
+import org.springframework.data.repository.query.Param;
 
 /**
  * Repository class for <code>Owner</code> domain objects. All method names are compliant
@@ -44,6 +47,51 @@ public interface OwnerRepository extends JpaRepository<Owner, Integer> {
 	 */
 	Page<Owner> findByLastNameStartingWith(String lastName, Pageable pageable);
 
+	/**
+	 * Internal method that retrieves raw data from the database. Use
+	 * findOwnerSearchResultsByLastName() instead.
+	 */
+	@Query(value = """
+			SELECT
+				o.id,
+				o.first_name,
+				o.last_name,
+				o.address,
+				o.city,
+				o.telephone,
+				COALESCE(GROUP_CONCAT(p.name ORDER BY p.name SEPARATOR ', '), '')
+			FROM owners o
+			LEFT JOIN pets p ON o.id = p.owner_id
+			WHERE LOWER(o.last_name) LIKE LOWER(CONCAT(:lastName, '%'))
+			GROUP BY o.id, o.first_name, o.last_name, o.address, o.city, o.telephone
+			""", countQuery = """
+			SELECT COUNT(DISTINCT o.id)
+			FROM owners o
+			WHERE LOWER(o.last_name) LIKE LOWER(CONCAT(:lastName, '%'))
+			""", nativeQuery = true)
+	Page<Object[]> findOwnerSearchResultsRaw(@Param("lastName") String lastName, Pageable pageable);
+
+	/**
+	 * Efficiently retrieve owner search results with aggregated pet names using a single
+	 * query. This uses a native query with GROUP_CONCAT to avoid N+1 queries.
+	 *
+	 * The results are projected into OwnerSearchResult DTOs.
+	 * @param lastName Value to search for
+	 * @param pageable Pagination parameters
+	 * @return Page of OwnerSearchResult DTOs
+	 */
+	default Page<OwnerSearchResult> findOwnerSearchResultsByLastName(String lastName, Pageable pageable) {
+		Page<Object[]> rawResults = findOwnerSearchResultsRaw(lastName, pageable);
+		return rawResults.map(row -> new OwnerSearchResult(((Number) row[0]).intValue(), // id
+				(String) row[1], // firstName
+				(String) row[2], // lastName
+				(String) row[3], // address
+				(String) row[4], // city
+				(String) row[5], // telephone
+				(String) row[6] // petNames
+		));
+	}
+
 	/**
 	 * Retrieve an {@link Owner} from the data store by id.
 	 * <p>
@@ -59,4 +107,24 @@ public interface OwnerRepository extends JpaRepository<Owner, Integer> {
 	 */
 	Optional<Owner> findById(Integer id);
 
+	/**
+	 * Retrieve an {@link Owner} with pets eagerly loaded using EntityGraph. Use this when
+	 * you need to display or work with the owner's pets.
+	 * @param id the id to search for
+	 * @return an {@link Optional} containing the {@link Owner} with pets loaded
+	 */
+	@EntityGraph(attributePaths = { "pets", "pets.type" })
+	@Query("SELECT o FROM Owner o WHERE o.id = :id")
+	Optional<Owner> findByIdWithPets(@Param("id") Integer id);
+
+	/**
+	 * Retrieve an {@link Owner} with complete data graph (pets, types, visits). Use this
+	 * for detail views where all related data is needed.
+	 * @param id the id to search for
+	 * @return an {@link Optional} containing the {@link Owner} with complete data
+	 */
+	@EntityGraph(attributePaths = { "pets", "pets.type", "pets.visits" })
+	@Query("SELECT o FROM Owner o WHERE o.id = :id")
+	Optional<Owner> findByIdWithPetsAndVisits(@Param("id") Integer id);
+
 }

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

@@ -0,0 +1,81 @@
+/*
+ * Copyright 2012-2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.samples.petclinic.owner;
+
+/**
+ * DTO for owner search results that efficiently includes aggregated pet names without
+ * triggering N+1 queries.
+ */
+public class OwnerSearchResult {
+
+	private final Integer id;
+
+	private final String firstName;
+
+	private final String lastName;
+
+	private final String address;
+
+	private final String city;
+
+	private final String telephone;
+
+	private final String petNames; // Comma-separated pet names
+
+	public OwnerSearchResult(Integer id, String firstName, String lastName, String address, String city,
+			String telephone, String petNames) {
+		this.id = id;
+		this.firstName = firstName;
+		this.lastName = lastName;
+		this.address = address;
+		this.city = city;
+		this.telephone = telephone;
+		this.petNames = petNames;
+	}
+
+	public Integer getId() {
+		return id;
+	}
+
+	public String getFirstName() {
+		return firstName;
+	}
+
+	public String getLastName() {
+		return lastName;
+	}
+
+	public String getAddress() {
+		return address;
+	}
+
+	public String getCity() {
+		return city;
+	}
+
+	public String getTelephone() {
+		return telephone;
+	}
+
+	public String getPetNames() {
+		return petNames != null ? petNames : "";
+	}
+
+	public boolean hasPets() {
+		return petNames != null && !petNames.trim().isEmpty();
+	}
+
+}

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

@@ -20,6 +20,7 @@ import java.util.Collection;
 import java.util.LinkedHashSet;
 import java.util.Set;
 
+import org.hibernate.annotations.BatchSize;
 import org.springframework.format.annotation.DateTimeFormat;
 import org.springframework.samples.petclinic.model.NamedEntity;
 
@@ -49,13 +50,18 @@ public class Pet extends NamedEntity {
 	@DateTimeFormat(pattern = "yyyy-MM-dd")
 	private LocalDate birthDate;
 
-	@ManyToOne(fetch = FetchType.LAZY)
+	// PetType can remain EAGER as it's a simple lookup entity
+	// and won't cause performance issues
+	@ManyToOne(fetch = FetchType.EAGER)
 	@JoinColumn(name = "type_id")
 	private PetType type;
 
+	// Changed from EAGER to LAZY to avoid cascading N+1 queries
+	// Added @BatchSize to optimize when visits are loaded
 	@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
 	@JoinColumn(name = "pet_id")
 	@OrderBy("date ASC")
+	@BatchSize(size = 10)
 	private final Set<Visit> visits = new LinkedHashSet<>();
 
 	public void setBirthDate(LocalDate birthDate) {

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

@@ -40,7 +40,7 @@ public class Visit extends BaseEntity {
 	@NotBlank
 	private String description;
 
-	@ManyToOne(fetch = FetchType.LAZY)
+	@ManyToOne(fetch = FetchType.EAGER)
 	@JoinColumn(name = "pet_id")
 	private Pet pet;
 

src/main/resources/templates/owners/ownersList.html

@@ -24,7 +24,7 @@
         <td th:text="${owner.address}" />
         <td th:text="${owner.city}" />
         <td th:text="${owner.telephone}" />
-        <td><span th:text="${#strings.listJoin(owner.pets, ', ')}" /></td>
+        <td><span th:text="${owner.petNames}" /></td>
       </tr>
     </tbody>
   </table>
@@ -58,4 +58,4 @@
   </div>
 </body>
 
-</html>
+</html>

src/test/java/org/springframework/samples/petclinic/PetClinicIntegrationTests.java

@@ -49,13 +49,12 @@ public class PetClinicIntegrationTests {
 		vets.findAll(); // served from cache
 	}
 
-	// @Test
-	// void testOwnerDetails() {
-	// RestTemplate template = builder.rootUri("http://localhost:" + port).build();
-	// ResponseEntity<String> result =
-	// template.exchange(RequestEntity.get("/owners/1").build(), String.class);
-	// assertThat(result.getStatusCode()).isEqualTo(HttpStatus.OK);
-	// }
+	@Test
+	void testOwnerDetails() {
+		RestTemplate template = builder.rootUri("http://localhost:" + port).build();
+		ResponseEntity<String> result = template.exchange(RequestEntity.get("/owners/1").build(), String.class);
+		assertThat(result.getStatusCode()).isEqualTo(HttpStatus.OK);
+	}
 
 	public static void main(String[] args) {
 		SpringApplication.run(PetClinicApplication.class, args);

src/test/java/org/springframework/samples/petclinic/owner/OwnerControllerTests.java

@@ -89,16 +89,25 @@ class OwnerControllerTests {
 
 	@BeforeEach
 	void setup() {
-
 		Owner george = george();
-		given(this.owners.findByLastNameStartingWith(eq("Franklin"), any(Pageable.class)))
-			.willReturn(new PageImpl<>(List.of(george)));
 
+		// Mock the optimized search method with DTOs
+		OwnerSearchResult georgeSearchResult = new OwnerSearchResult(TEST_OWNER_ID, "George", "Franklin",
+				"110 W. Liberty St.", "Madison", "6085551023", "Max");
+
+		given(this.owners.findOwnerSearchResultsByLastName(eq("Franklin"), any(Pageable.class)))
+			.willReturn(new PageImpl<>(List.of(georgeSearchResult)));
+
+		// Mock EntityGraph methods for edit/detail views
+		given(this.owners.findByIdWithPets(TEST_OWNER_ID)).willReturn(Optional.of(george));
+		given(this.owners.findByIdWithPetsAndVisits(TEST_OWNER_ID)).willReturn(Optional.of(george));
+
+		// Keep old method for backward compatibility
 		given(this.owners.findById(TEST_OWNER_ID)).willReturn(Optional.of(george));
+
 		Visit visit = new Visit();
 		visit.setDate(LocalDate.now());
 		george.getPet("Max").getVisits().add(visit);
-
 	}
 
 	@Test
@@ -141,15 +150,27 @@ class OwnerControllerTests {
 
 	@Test
 	void testProcessFindFormSuccess() throws Exception {
-		Page<Owner> tasks = new PageImpl<>(List.of(george(), new Owner()));
-		when(this.owners.findByLastNameStartingWith(anyString(), any(Pageable.class))).thenReturn(tasks);
+		// Create search results using DTOs
+		OwnerSearchResult result1 = new OwnerSearchResult(1, "George", "Franklin", "110 W. Liberty St.", "Madison",
+				"6085551023", "Max");
+		OwnerSearchResult result2 = new OwnerSearchResult(2, "Betty", "Davis", "638 Cardinal Ave.", "Sun Prairie",
+				"6085551749", "Basil");
+
+		Page<OwnerSearchResult> tasks = new PageImpl<>(List.of(result1, result2));
+		when(this.owners.findOwnerSearchResultsByLastName(anyString(), any(Pageable.class))).thenReturn(tasks);
+
 		mockMvc.perform(get("/owners?page=1")).andExpect(status().isOk()).andExpect(view().name("owners/ownersList"));
 	}
 
 	@Test
 	void testProcessFindFormByLastName() throws Exception {
-		Page<Owner> tasks = new PageImpl<>(List.of(george()));
-		when(this.owners.findByLastNameStartingWith(eq("Franklin"), any(Pageable.class))).thenReturn(tasks);
+		// Single result - should redirect
+		OwnerSearchResult result = new OwnerSearchResult(TEST_OWNER_ID, "George", "Franklin", "110 W. Liberty St.",
+				"Madison", "6085551023", "Max");
+
+		Page<OwnerSearchResult> tasks = new PageImpl<>(List.of(result));
+		when(this.owners.findOwnerSearchResultsByLastName(eq("Franklin"), any(Pageable.class))).thenReturn(tasks);
+
 		mockMvc.perform(get("/owners?page=1").param("lastName", "Franklin"))
 			.andExpect(status().is3xxRedirection())
 			.andExpect(view().name("redirect:/owners/" + TEST_OWNER_ID));
@@ -157,14 +178,15 @@ class OwnerControllerTests {
 
 	@Test
 	void testProcessFindFormNoOwnersFound() throws Exception {
-		Page<Owner> tasks = new PageImpl<>(List.of());
-		when(this.owners.findByLastNameStartingWith(eq("Unknown Surname"), any(Pageable.class))).thenReturn(tasks);
+		Page<OwnerSearchResult> tasks = new PageImpl<>(List.of());
+		when(this.owners.findOwnerSearchResultsByLastName(eq("Unknown Surname"), any(Pageable.class)))
+			.thenReturn(tasks);
+
 		mockMvc.perform(get("/owners?page=1").param("lastName", "Unknown Surname"))
 			.andExpect(status().isOk())
 			.andExpect(model().attributeHasFieldErrors("owner", "lastName"))
 			.andExpect(model().attributeHasFieldErrorCode("owner", "lastName", "notFound"))
 			.andExpect(view().name("owners/findOwners"));
-
 	}
 
 	@Test
@@ -240,7 +262,7 @@ class OwnerControllerTests {
 		owner.setCity("New York");
 		owner.setTelephone("0123456789");
 
-		when(owners.findById(pathOwnerId)).thenReturn(Optional.of(owner));
+		when(owners.findByIdWithPets(pathOwnerId)).thenReturn(Optional.of(owner));
 
 		mockMvc.perform(MockMvcRequestBuilders.post("/owners/{ownerId}/edit", pathOwnerId).flashAttr("owner", owner))
 			.andExpect(status().is3xxRedirection())