Kod źródłowy do wpisu o Spring Boot - Spring Data JPA część II: Powiązania między tabelami znajdującego się pod adresem https://blog.mloza.pl/spring-boot-spring-data-jpa-czesc-ii-powiazania-miedzy-tabelami/

addTask.java

    @RequestMapping("/add-task")
    @ResponseBody
    public String addTask() {
        Project project = projectRepository.findOne(1);

        Task task = new Task()
               .withBudget(12.00)
               .withDescription("New task")
               .withName("New task")
               .withProject(project);  // 1

        project.getTasks().add(task);  // 2

        taskRepository.save(task);

        return projectsAndTasks();
    }

deleteTask.java

    @RequestMapping("/delete-task")
    @ResponseBody
    public String deleteTask() {
        Task task = taskRepository.findOne(1L);
        Project project = task.getProject();

        project.getTasks().remove(task);
        taskRepository.delete(task);

        return projectsAndTasks();
    }

ManyToMany.java

    @ManyToMany
    private List<Project> projects;

ManyToMany2.java

    @ManyToMany(mappedBy = "projects")
    private List<Tag> tags;

ManyToOne.java

    @ManyToOne
    private Project project;

OneToMany.java

    @OneToMany(mappedBy = "project")
    private List<Task> tasks;

OneToOne.java

    @OneToOne
    Project project;

OneToOne2.java

    @OneToOne(mappedBy = "project")
    private ProjectDetails projectDetails;

Project.java

@Entity
public class Project {
    @GeneratedValue
    @Id
    private int id;

    @Column
    private String name;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Project{" +
                "id=" + id +
                ", name='" + name + '\'' +
                "}";

    }
}

ProjectDetails.java

@Entity
public class ProjectDetails {
    @GeneratedValue
    @Id
    private int id;

    @Column
    private String description;

    // pomijam gettery i settery dla czytelności

    @Override
    public String toString() {
        return "ProjectDetails{" +
                "id=" + id +
                ", description='" + description + '\'' +
                '}';
    }

}

ProjectDetailsRepository.java

public interface ProjectDetailsRepository extends CrudRepository<ProjectDetails, Integer> { }

ProjectRepository.java

public interface ProjectRepository extends CrudRepository<Project, Integer> { }

projectsAndTasks.java

    @Autowired
    public ProjectRepository projectRepository;

    @RequestMapping("/project-tasks")
    @ResponseBody
    public String projectsAndTasks() {
        StringBuilder response = new StringBuilder();

        for(Project project: projectRepository.findAll()) {
            response.append(project).append("<br>");
            for(Task task: project.getTasks()) {      // 1
                response.append("- ").append(task).append("<br>");
            }
        }

        return response.toString();
    }

projectsByTag.java

    @RequestMapping("/by-tag")
    @ResponseBody
    public String projectsByTag() {
        StringBuilder out = new StringBuilder();
        tagRepository.findAll().forEach(tag -> {
            out.append("tag: ").append(tag.getName()).append("<br>");
            tag.getProjects().forEach(project -> {
                out.append("- ").append(project.getName()).append("<br>");
            });
        });
        return out.toString();
    }

removeTag.java

    @RequestMapping("/remove-tag")
    @ResponseBody
    public String removeTag() {
        Optional<Project> project =
                StreamSupport
                        .stream(projectRepository
                                .findAll()
                                .spliterator(), false)
                        .filter(p -> p.getName().equals("Project 2"))
                        .findAny();

        project.ifPresent(p -> {
            Optional<Tag> tag = p.getTags().stream()
                    .filter(t -> t.getName().equals("Tag 2"))
                    .findAny();

            tag.ifPresent(t -> {
                t.getProjects().remove(p);
                p.getTags().remove(t);

                tagRepository.save(t);
                projectRepository.save(p);
            });
        });

        return "OK";
    }

Tag.java

@Entity
public class Tag {
    
    @GeneratedValue
    @Id
    private int id;
    
    private String name;

    // Gettery i settery
}

TagRepository.java

public interface TagRepository extends CrudRepository<Tag, Integer> { }

tagsAndProjects.java

    @Autowired
    public TagRepository tagRepository;

    @RequestMapping("/tagging")
    @ResponseBody
    public String tagsAndProjects() {
        Tag tag1 = new Tag();
        tag1.setName("Tag 1");

        Tag tag2 = new Tag();
        tag2.setName("Tag 2");

        Project project1 = new Project();
        project1.setName("Project 1");

        Project project2 = new Project();
        project2.setName("Project 2");
        projectRepository.save(project1);
        projectRepository.save(project2);

        project1.setTags(new ArrayList<>());
        project1.getTags().add(tag1);

        project2.setTags(new ArrayList<>());
        project2.getTags().add(tag1);
        project2.getTags().add(tag2);

        tag1.setProjects(new ArrayList<>());
        tag1.getProjects().add(project1);
        tag1.getProjects().add(project2);

        tag2.setProjects(new ArrayList<>());
        tag2.getProjects().add(project2);

        tagRepository.save(tag1);
        tagRepository.save(tag2);

        return "OK";
    }

tagsByProject.java

    @RequestMapping("/by-project")
    @ResponseBody
    public String tagsByProject() {
        StringBuilder out = new StringBuilder();
        projectRepository.findAll().forEach(project -> { // 1
            out.append("project: ").append(project.getName()).append("<br>");
            project.getTags().forEach(tag -> { // 2
                out.append("- ").append(tag.getName()).append("<br>");
            });
        });
        return out.toString();
    }