Java Spring数据JPA多通双向

问题：在我尝试向数据库中添加学生OBEJCT之前，它一直有效，但表的创建是正确的。 我不能再简化这篇文章了。但它主要是不需要大量阅读的代码，它是一个简单的spring数据存储库服务模型。我发布这一切都是因为idk我做错了什么。问题在于JPA映射。 我从这里得到了这个例子

MDOELS

@Entity
public class Department {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private int id;
    private String name;

    @OneToMany(mappedBy="department")
    private Collection<Student> students;

    public Department() {
    }

    public Department(String name) {
        this.name = name;
    }

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public Collection<Student> getStudents() {
        return students;
    }

    public void setStudent(Collection<Student> students) {
        this.students = students;
    }

    public String toString() {
        return "Department id: " + getId() +
                ", name: " + getName();
    }
}



@Entity
public class Student {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private int id;
    private String name;

    @ManyToOne (cascade=CascadeType.ALL)
    private Department department;

    public Student() {
    }

    public Student(String name, Department department) {
        this.name = name;
        this.department = department;
    }

    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;
    }



    public Department getDepartment() {
        return department;
    }

    public void setDepartment(Department department) {
        this.department = department;
    }

    public String toString() {
        return "\n\nID:" + id + "\nName:" + name + "\n\n" + department;
    }
}

---

我不能完全理解你们的问题，但我想补充一点。添加操作的级联未实现或不完整。希望对您有所帮助。

您添加了cascade=CascadeType.ALL for Department in Student class，并将departments单独保存<代码>this.departmentService.addToDataBase（部门）

修理工：不要打电话

departmentService.addToDataBase(departments);

---

或者从Student中删除CascadeType.ALL

为什么每个人都在他们的示例中添加CascadeType，而当我添加它时，它会破坏一切？它没有破坏一切，您添加CascadeType并尝试管理部门。你混淆了两个概念。如果只添加级联，它应该可以工作。此外，如果您只与学生分开的部门合作（在保存学生时不要试图保存部门），那么它也应该起作用。您是否有这样的示例，即他们同时具有级联类型和管理的cacsadede实体？sbjavateam i首先添加部门，然后添加学生？在我的主要方法中，在主类中的示例中，保存了student-em.persist（student）；但是部门没有相同的名称，没有em.persist（dept）。系作为studentWho的一部分创建，谁是关系的所有者？从学生到系的外键。有什么地方可以让我用JPACan学习spring boot数据吗？你可以把

@JoinColumn

添加到部门顶部吗？我可以邀请stackoverflow聊天一会儿，向我解释级联类型吗？在关系上使用级联类型注释，自动对其子关系实体执行插入删除等操作。

@Service
public class StudentService {
    private final StudentRepository studentRepository;

    @Autowired
    public StudentService(StudentRepository studentRepository) {
        this.studentRepository = studentRepository;

    }

    public void addToDatabase(Student student) {
        this.studentRepository.saveAndFlush(student);

    }

    public Student getStudentByName(String name) {
        return studentRepository.findByName(name);
    }
}
@Service
public class DepartmentService {
    private final DepartmentRepository departmentRepository;

    @Autowired
    public DepartmentService(DepartmentRepository departmentRepository) {
        this.departmentRepository = departmentRepository;

    }

    public void addToDataBase(List<Department> department) {
        this.departmentRepository.save(department);
        department.forEach(this.departmentRepository::saveAndFlush);
    }
    public Department getDepartmentByName(String name){
        return  this.departmentRepository.findByName(name);
    }
}

@Component
public class Terminal implements CommandLineRunner {
    private final StudentService studentService;
    private final DepartmentService departmentService;

    @Autowired
    public Terminal(StudentService studentService, DepartmentService departmentService) {
        this.studentService = studentService;
        this.departmentService = departmentService;
    }

        @Override
        public void run(String... strings) throws Exception {
            Department department = new Department("dep1");
            Department department1 = new Department("dep2");
            Department department2 = new Department("dep3");
            Department department3 = new Department("dep4");
            List<Department> departments = new ArrayList<>(Arrays.asList(department, department1, department2, department3));
            this.departmentService.addToDataBase(departments);
    //
            Student student = new Student("pesho", department);
            Student student11 = new Student("gosho", department1);
            this.studentService.addToDatabase(student11);
            this.studentService.addToDatabase(student);
            student = new Student("sasho", department2);
            this.studentService.addToDatabase(student);
    //        System.out.println(this.studentService.getStudentByName("gosho").getDepartment1());
    //        System.out.println("CHECKING ONE TO ONE BIDIRECTIONAL: " + this.departmentService.getDepartmentByName("dep1").getStudent());

        }
    }

Caused by: org.hibernate.PersistentObjectException: detached entity passed to persist: app.models.Department

departmentService.addToDataBase(departments);