Bael 7452 updated (#15714)

* BAEL-7452: Lazy loaded lists

* BAEL-7452: Example with Lazy Lists

* BAEL-7452: Test for lazy groups

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/eager/set/lazy/moderatedomain/Application.java

@@ -0,0 +1,8 @@
+package com.baeldung.listvsset.eager.set.lazy.moderatedomain;
+
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class Application {
+
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/eager/set/lazy/moderatedomain/Group.java

@@ -0,0 +1,22 @@
+package com.baeldung.listvsset.eager.set.lazy.moderatedomain;
+
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.ManyToMany;
+import jakarta.persistence.Table;
+import java.util.Set;
+import lombok.Data;
+
+@Data
+@Entity(name = "interest_group")
+@Table(name = "interest_group")
+public class Group {
+
+    @Id
+    private Long id;
+
+    private String name;
+
+    @ManyToMany
+    private Set<User> members;
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/eager/set/lazy/moderatedomain/GroupRepository.java

@@ -0,0 +1,7 @@
+package com.baeldung.listvsset.eager.set.lazy.moderatedomain;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+
+public interface GroupRepository extends JpaRepository<Group, Long> {
+
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/eager/set/lazy/moderatedomain/GroupService.java

@@ -0,0 +1,29 @@
+package com.baeldung.listvsset.eager.set.lazy.moderatedomain;
+
+import java.util.List;
+import java.util.Optional;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Service;
+
+@Service
+public class GroupService {
+
+    private final GroupRepository groupRepository;
+
+    @Autowired
+    public GroupService(GroupRepository groupRepository) {
+        this.groupRepository = groupRepository;
+    }
+
+    public Optional<Group> findById(Long aLong) {
+        return groupRepository.findById(aLong);
+    }
+
+    public List<Group> findAll() {
+        return groupRepository.findAll();
+    }
+
+    public void save(Group group) {
+        groupRepository.save(group);
+    }
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/eager/set/lazy/moderatedomain/Post.java

@@ -0,0 +1,43 @@
+package com.baeldung.listvsset.eager.set.lazy.moderatedomain;
+
+import com.fasterxml.jackson.annotation.JsonBackReference;
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.Lob;
+import jakarta.persistence.ManyToOne;
+import java.util.Objects;
+import lombok.Data;
+
+@Entity
+@Data
+public class Post {
+
+    @Id
+    private Long id;
+
+    @Lob
+    private String content;
+
+    @JsonBackReference
+    @ManyToOne
+    private User author;
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+
+        Post post = (Post) o;
+
+        return Objects.equals(id, post.id);
+    }
+
+    @Override
+    public int hashCode() {
+        return id != null ? id.hashCode() : 0;
+    }
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/eager/set/lazy/moderatedomain/PostRepository.java

@@ -0,0 +1,7 @@
+package com.baeldung.listvsset.eager.set.lazy.moderatedomain;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+
+public interface PostRepository extends JpaRepository<Post, Long> {
+
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/eager/set/lazy/moderatedomain/User.java

@@ -0,0 +1,45 @@
+package com.baeldung.listvsset.eager.set.lazy.moderatedomain;
+
+import com.fasterxml.jackson.annotation.JsonManagedReference;
+import jakarta.persistence.CascadeType;
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.OneToMany;
+import jakarta.persistence.Table;
+import java.util.Objects;
+import java.util.Set;
+import lombok.Data;
+
+@Data
+@Entity(name = "simple_user")
+@Table(name = "simple_user")
+public class User {
+
+    @Id
+    private Long id;
+    private String username;
+    private String email;
+
+    @JsonManagedReference
+    @OneToMany(cascade = CascadeType.ALL, mappedBy = "author")
+    protected Set<Post> posts;
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+
+        User user = (User) o;
+
+        return Objects.equals(id, user.id);
+    }
+
+    @Override
+    public int hashCode() {
+        return id != null ? id.hashCode() : 0;
+    }
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/eager/set/lazy/moderatedomain/UserRepository.java

@@ -0,0 +1,7 @@
+package com.baeldung.listvsset.eager.set.lazy.moderatedomain;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+
+public interface UserRepository extends JpaRepository<User, Long> {
+
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/eager/set/lazy/moderatedomain/UserService.java

@@ -0,0 +1,20 @@
+package com.baeldung.listvsset.eager.set.lazy.moderatedomain;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Transactional
+@Service
+public class UserService extends com.baeldung.listvsset.Service<User> {
+
+    public UserService(JpaRepository<User, Long> repository) {
+        super(repository);
+    }
+
+    @Override
+    public UserRepository getRepository() {
+        return ((UserRepository) super.getRepository());
+    }
+
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/lazy/list/moderatedomain/Application.java

@@ -0,0 +1,8 @@
+package com.baeldung.listvsset.lazy.list.moderatedomain;
+
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class Application {
+
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/lazy/list/moderatedomain/Group.java

@@ -0,0 +1,22 @@
+package com.baeldung.listvsset.lazy.list.moderatedomain;
+
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.ManyToMany;
+import jakarta.persistence.Table;
+import java.util.List;
+import lombok.Data;
+
+@Data
+@Entity(name = "interest_group")
+@Table(name = "interest_group")
+public class Group {
+
+    @Id
+    private Long id;
+
+    private String name;
+
+    @ManyToMany
+    private List<User> members;
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/lazy/list/moderatedomain/GroupRepository.java

@@ -0,0 +1,7 @@
+package com.baeldung.listvsset.lazy.list.moderatedomain;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+
+public interface GroupRepository extends JpaRepository<Group, Long> {
+
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/lazy/list/moderatedomain/GroupService.java

@@ -0,0 +1,35 @@
+package com.baeldung.listvsset.lazy.list.moderatedomain;
+
+import java.util.List;
+import java.util.Optional;
+import java.util.function.ToIntFunction;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Service
+@Transactional
+public class GroupService {
+
+    private final GroupRepository groupRepository;
+
+    @Autowired
+    public GroupService(GroupRepository groupRepository) {
+        this.groupRepository = groupRepository;
+    }
+
+    public Optional<Group> findById(Long aLong) {
+        return groupRepository.findById(aLong);
+    }
+
+    public List<Group> findAll() {
+        return groupRepository.findAll();
+    }
+    public int countNumberOfRequestsWithFunction(ToIntFunction<List<Group>> function) {
+        return function.applyAsInt(groupRepository.findAll());
+    }
+
+    public <S extends Group> S save(S entity) {
+        return groupRepository.save(entity);
+    }
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/lazy/list/moderatedomain/Post.java

@@ -0,0 +1,23 @@
+package com.baeldung.listvsset.lazy.list.moderatedomain;
+
+import com.fasterxml.jackson.annotation.JsonBackReference;
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.Lob;
+import jakarta.persistence.ManyToOne;
+import lombok.Data;
+
+@Entity
+@Data
+public class Post {
+
+    @Id
+    private Long id;
+
+    @Lob
+    private String content;
+
+    @JsonBackReference
+    @ManyToOne
+    private User author;
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/lazy/list/moderatedomain/PostRepository.java

@@ -0,0 +1,7 @@
+package com.baeldung.listvsset.lazy.list.moderatedomain;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+
+public interface PostRepository extends JpaRepository<Post, Long> {
+
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/lazy/list/moderatedomain/User.java

@@ -0,0 +1,45 @@
+package com.baeldung.listvsset.lazy.list.moderatedomain;
+
+import com.fasterxml.jackson.annotation.JsonManagedReference;
+import jakarta.persistence.CascadeType;
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.OneToMany;
+import jakarta.persistence.Table;
+import java.util.List;
+import java.util.Objects;
+import lombok.Data;
+
+@Data
+@Entity(name = "simple_user")
+@Table(name = "simple_user")
+public class User {
+
+    @Id
+    private Long id;
+    private String username;
+    private String email;
+
+    @JsonManagedReference
+    @OneToMany(cascade = CascadeType.ALL, mappedBy = "author")
+    protected List<Post> posts;
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+
+        User user = (User) o;
+
+        return Objects.equals(id, user.id);
+    }
+
+    @Override
+    public int hashCode() {
+        return id != null ? id.hashCode() : 0;
+    }
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/lazy/list/moderatedomain/UserRepository.java

@@ -0,0 +1,7 @@
+package com.baeldung.listvsset.lazy.list.moderatedomain;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+
+public interface UserRepository extends JpaRepository<User, Long> {
+
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/listvsset/lazy/list/moderatedomain/UserService.java

@@ -0,0 +1,20 @@
+package com.baeldung.listvsset.lazy.list.moderatedomain;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Transactional
+@Service
+public class UserService extends com.baeldung.listvsset.Service<User> {
+
+    public UserService(JpaRepository<User, Long> repository) {
+        super(repository);
+    }
+
+    @Override
+    public UserRepository getRepository() {
+        return ((UserRepository) super.getRepository());
+    }
+
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/nplusone/defaultfetch/list/Application.java

@@ -0,0 +1,8 @@
+package com.baeldung.nplusone.defaultfetch.list;
+
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class Application {
+
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/nplusone/defaultfetch/list/Post.java

@@ -0,0 +1,23 @@
+package com.baeldung.nplusone.defaultfetch.list;
+
+import com.fasterxml.jackson.annotation.JsonBackReference;
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.Lob;
+import jakarta.persistence.ManyToOne;
+import lombok.Data;
+
+@Entity
+@Data
+public class Post {
+
+    @Id
+    private Long id;
+
+    @Lob
+    private String content;
+
+    @JsonBackReference
+    @ManyToOne
+    private User author;
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/nplusone/defaultfetch/list/PostRepository.java

@@ -0,0 +1,7 @@
+package com.baeldung.nplusone.defaultfetch.list;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+
+public interface PostRepository extends JpaRepository<Post, Long> {
+
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/nplusone/defaultfetch/list/User.java

@@ -0,0 +1,25 @@
+package com.baeldung.nplusone.defaultfetch.list;
+
+import com.fasterxml.jackson.annotation.JsonManagedReference;
+import jakarta.persistence.CascadeType;
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.OneToMany;
+import jakarta.persistence.Table;
+import java.util.List;
+import lombok.Data;
+
+@Data
+@Entity(name = "simple_user")
+@Table(name = "simple_user")
+public class User {
+
+    @Id
+    private Long id;
+    private String username;
+    private String email;
+
+    @JsonManagedReference
+    @OneToMany(cascade = CascadeType.ALL, mappedBy = "author")
+    protected List<Post> posts;
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/nplusone/defaultfetch/list/UserRepository.java

@@ -0,0 +1,9 @@
+package com.baeldung.nplusone.defaultfetch.list;
+
+import org.springframework.context.annotation.Lazy;
+import org.springframework.data.jpa.repository.JpaRepository;
+
+@Lazy(value = false)
+public interface UserRepository extends JpaRepository<User, Long> {
+
+}

persistence-modules/spring-boot-persistence-4/src/main/java/com/baeldung/nplusone/defaultfetch/list/UserService.java

@@ -0,0 +1,20 @@
+package com.baeldung.nplusone.defaultfetch.list;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Transactional
+@Service
+public class UserService extends com.baeldung.listvsset.Service<User> {
+
+    public UserService(JpaRepository<User, Long> repository) {
+        super(repository);
+    }
+
+    @Override
+    public UserRepository getRepository() {
+        return ((UserRepository) super.getRepository());
+    }
+
+}

persistence-modules/spring-boot-persistence-4/src/test/java/com/baeldung/listvsset/lazy/list/NPlusOneLazyModerateDomainIntegrationTest.java

@@ -0,0 +1,77 @@
+package com.baeldung.listvsset.lazy.list;
+
+import static com.vladmihalcea.sql.SQLStatementCountValidator.assertSelectCount;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.baeldung.listvsset.BaseNPlusOneIntegrationTest;
+import com.baeldung.listvsset.lazy.list.moderatedomain.Application;
+import com.baeldung.listvsset.lazy.list.moderatedomain.Group;
+import com.baeldung.listvsset.lazy.list.moderatedomain.GroupService;
+import com.baeldung.listvsset.lazy.list.moderatedomain.User;
+import com.baeldung.listvsset.util.TestConfig;
+import java.util.Collection;
+import java.util.List;
+import java.util.Optional;
+import java.util.stream.Collectors;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+
+@SpringBootTest(classes = {Application.class, TestConfig.class}, properties = {
+  "hibernate.show_sql=true",
+  "logging.level.org.hibernate.SQL=debug",
+  "logging.level.org.hibernate.orm.jdbc.bind=trace"
+})
+class NPlusOneLazyModerateDomainIntegrationTest extends BaseNPlusOneIntegrationTest<User> {
+
+    @Autowired
+    private GroupService groupService;
+
+    @Test
+    void givenLazyListBasedUser_whenFetchingAllUsers_thenIssueOneRequest() {
+        getService().findAll();
+        assertSelectCount(1);
+    }
+
+    @ParameterizedTest
+    @ValueSource(longs = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10})
+    void givenLazyListBasedUser_whenFetchingOneUser_thenIssueOneRequest(Long id) {
+        getService().getUserById(id);
+        assertSelectCount(1);
+    }
+
+    @Test
+    void givenLazyListBasedGroup_whenFetchingAllGroups_thenIssueOneRequest() {
+        groupService.findAll();
+        assertSelectCount(1);
+    }
+    @Test
+    void givenLazyListBasedGroup_whenFilteringGroups_thenIssueNPlusOneRequests() {
+        int numberOfRequests = groupService.countNumberOfRequestsWithFunction(groups -> {
+            groups.stream()
+              .map(Group::getMembers)
+              .flatMap(Collection::stream)
+              .collect(Collectors.toSet());
+            return groups.size();
+        });
+        assertSelectCount(numberOfRequests + 1);
+    }
+
+    @ParameterizedTest
+    @ValueSource(longs = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10})
+    void givenLazyListBasedGroup_whenFetchingAllGroups_thenIssueOneRequest(Long groupId) {
+        Optional<Group> group = groupService.findById(groupId);
+        assertThat(group).isPresent();
+        assertSelectCount(1);
+    }
+
+    protected void addUsers() {
+        List<User> users = jsonUtils.getUsers(User.class);
+        databaseUtil.saveAll(users);
+        List<Group> groups = jsonUtils.getGroupsWithMembers(Group.class);
+        databaseUtil.saveAll(groups);
+    }
+
+}

persistence-modules/spring-boot-persistence-4/src/test/java/com/baeldung/listvsset/lazy/list/NPlusOneLazySimpleDomainIntegrationTest.java

@@ -0,0 +1,55 @@
+package com.baeldung.listvsset.lazy.list;
+
+import static com.vladmihalcea.sql.SQLStatementCountValidator.assertSelectCount;
+
+import com.baeldung.listvsset.BaseNPlusOneIntegrationTest;
+import com.baeldung.listvsset.util.TestConfig;
+import com.baeldung.nplusone.defaultfetch.list.Application;
+import com.baeldung.nplusone.defaultfetch.list.Post;
+import com.baeldung.nplusone.defaultfetch.list.User;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+import org.springframework.boot.test.context.SpringBootTest;
+
+@SpringBootTest(classes = {Application.class, TestConfig.class}, properties = {
+  "hibernate.show_sql=true",
+  "logging.level.org.hibernate.SQL=debug",
+  "logging.level.org.hibernate.orm.jdbc.bind=trace"
+})
+class NPlusOneLazySimpleDomainIntegrationTest extends BaseNPlusOneIntegrationTest<User> {
+
+    @Test
+    void givenLazyListBasedUser_WhenFetchingAllUsers_ThenIssueOneRequests() {
+        getService().findAll();
+        assertSelectCount(1);
+    }
+
+    @Test
+    void givenLazyListBasedUser_WhenFetchingAllUsersCheckingPosts_ThenIssueNPlusOneRequests() {
+        int numberOfRequests = getService().countNumberOfRequestsWithFunction(users -> {
+            List<List<Post>> usersWithPosts
+              = users.stream()
+              .map(User::getPosts)
+              .filter(List::isEmpty)
+              .toList();
+            return users.size();
+        });
+        assertSelectCount(numberOfRequests + 1);
+    }
+
+    @ParameterizedTest
+    @ValueSource(longs = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10})
+    void givenLazyListBasedUser_WhenFetchingOneUser_ThenIssueTwoRequest(Long id) {
+        getService().getUserByIdWithPredicate(id, user -> !user.getPosts().isEmpty());
+        assertSelectCount(2);
+    }
+
+
+    protected void addUsers() {
+        List<User> users = jsonUtils.getUsers(User.class);
+        databaseUtil.saveAll(users);
+    }
+
+}