java—从spring获取数据时，一些数据会多次显示

cu6pst1q  于 2021-07-15  发布在  Java
关注(0)|答案(1)|浏览(339)

我在java spring中有一个用于学习的数据库：

如果员工没有借来的书，所有的工作。
如果员工有2本书（或更多），并且该员工注册了任何课程，那么我在同一课程中看到该员工2次（如果他有3本书，那么3次，4次，等等）。

如果我使用查询“select*from registration”就可以了

github上的项目-https://github.com/katzzer/sqldemoapplicationnewversion
显示数据库数据的控制器

  1. @GetMapping("/employees/courseDetail")
  2.     public String getCourses(@RequestParam("courseId") long id, Model model) {
  3.         Optional<Course> courseOptional = courseService.getCourse(id);
  4.         if (courseOptional.isEmpty()) {
  5.             return "redirect:/employees/courses/";
  6.         }
  7.         Course course = courseOptional.get();
  8.         model.addAttribute("course", course);
  9.         List<Employee> employees = employeeService.getAllEmployees();
  10.         model.addAttribute("employees", employees);
  11.         List<Employee> enrolledEmployees = course.getEmployees();
  12.         model.addAttribute("enrolledEmployees", enrolledEmployees);
  14.         return "CourseDetailPage";
  15.     }

员工类别：

  1. @Entity(name = "Employee")
  2. @Table(name = "employee")
  3. @Transactional
  4. public class Employee {
  6.     @Id
  7.     @SequenceGenerator(
  8.             name = "employee_sequence",
  9.             sequenceName = "employee_sequence",
  10.             allocationSize = 1
  11.     )
  12.     @GeneratedValue(
  13.             strategy = GenerationType.SEQUENCE,
  14.             generator = "employee_sequence"
  15.     )
  16.     @Column(name ="id")
  17.     private Long id;
  19.     @Column(
  20.             name = "name",
  21.             nullable = false,
  22.             columnDefinition = "TEXT"
  23.     )
  24.     private String name;
  26.     @Column(
  27.             name = "city",
  28.             nullable = false,
  29.             columnDefinition = "TEXT"
  30.     )
  31.     private String city;
  33.     @Column(
  34.             name = "language",
  35.             nullable = false,
  36.             columnDefinition = "TEXT"
  37.     )
  38.     private String language;
  40.     @OneToOne(
  41.             mappedBy = "employee",
  42.             orphanRemoval = true,
  43.             cascade = {CascadeType.PERSIST, CascadeType.REMOVE}
  44.     )
  45.     private EmployeeIdCard employeeIdCard;
  47.     @OneToMany(
  48.             mappedBy = "employee",
  49.             orphanRemoval = true,
  50.             cascade = {CascadeType.PERSIST, CascadeType.REMOVE},
  51.             fetch = FetchType.EAGER
  52.     )
  53.     private List<Book> books = new ArrayList<>();
  55.     @ManyToMany(
  56.             cascade = {CascadeType.PERSIST, CascadeType.REMOVE},
  57.             fetch = FetchType.EAGER
  58.     )
  59.     @Fetch(value = FetchMode.SUBSELECT)
  60.     @JoinTable(
  61.             name = "enrolment",
  62.             joinColumns = @JoinColumn(
  63.                     name = "employee_id",
  64.                     foreignKey = @ForeignKey(name = "enrolment_employee_id_fk")
  65.             ),
  66.             inverseJoinColumns = @JoinColumn(
  67.                     name = "course_id",
  68.                     foreignKey = @ForeignKey(name = "enrolment_course_id_fk")   
  69.             )
  70.     )
  71.     private List<Course> courses = new ArrayList<>();
  73.     public Employee(String name, String city, String language) {
  74.         this.name = name;
  75.         this.city = city;
  76.         this.language = language;
  77.     }
  79.     public Employee(String name, String city, String language, EmployeeIdCard employeeIdCard) {
  80.         this.name = name;
  81.         this.city = city;
  82.         this.language = language;
  83.         this.employeeIdCard = employeeIdCard;
  84.     }
  86.     public Employee() {
  88.     }
  90.     public void addBook(Book book) {
  91.         if (!this.books.contains(book)) {
  92.             this.books.add(book);
  93.             book.setEmployee(this);
  94.         }
  95.     }
  97.     public void removeBook(Book book) {
  98.         if (this.books.contains(book)) {
  99.             this.books.remove(book);
  100.             book.setEmployee(null);
  101.         }
  102.     }
  104.     public void setEmployeeIdCard(EmployeeIdCard employeeIdCard) {
  105.         this.employeeIdCard = employeeIdCard;
  106.     }
  108.     public List<Book> getBooks() {
  109.         return books;
  110.     }
  112.     public Long getId() {
  113.         return id;
  114.     }
  116.     public void setId(Long id) {
  117.         this.id = id;
  118.     }
  120.     public String getName() {
  121.         return name;
  122.     }
  124.     public void setName(String name) {
  125.         this.name = name;
  126.     }
  128.     public String getCity() {
  129.         return city;
  130.     }
  132.     public void setCity(String city) {
  133.         this.city = city;
  134.     }
  136.     public String getLanguage() {
  137.         return language;
  138.     }
  140.     public void setLanguage(String language) {
  141.         this.language = language;
  142.     }
  144.     public EmployeeIdCard getEmployeeIdCard() {
  145.         return employeeIdCard;
  146.     }
  148.     public void setBooks(List<Book> books) {
  149.         this.books = books;
  150.     }
  152.     public List<Course> getCourses() {
  153.         return courses;
  154.     }
  156.     public void enrolToCourse(Course course) {
  157.         courses.add(course);
  158.         course.getEmployees().add(this);
  159.     }
  161.     public void unEnrolToCourse(Course course) {
  162.         courses.remove(course);
  163.         course.getEmployees().remove(this);

图书类

  1. @Entity(name = "Book")
  2. @Table(name = "book")
  3. public class Book {
  5.     @Id
  6.     @SequenceGenerator(
  7.             name = "book_sequence",
  8.             sequenceName = "book_sequence",
  9.             allocationSize = 1
  10.     )
  11.     @GeneratedValue(
  12.             strategy = SEQUENCE,
  13.             generator = "book_sequence"
  14.     )
  15.     @Column(
  16.             name = "id",
  17.             updatable = false
  18.     )
  19.     private Long id;
  21.     @Column(
  22.             name = "created_at",
  23.             nullable = false,
  24.             columnDefinition = "TIMESTAMP WITHOUT TIME ZONE"
  25.     )
  26.     private LocalDateTime createdAt;
  28.     @Column(
  29.             name = "book_name",
  30.             nullable = false
  31.     )
  32.     private String bookName;
  34.     @ManyToOne (fetch = FetchType.EAGER)
  35.     @JoinColumn(
  36.             name = "employee_id",
  37. //            nullable = false,
  38.             referencedColumnName = "id",
  39.             foreignKey = @ForeignKey (
  40.                     name = "employee_book_fk"
  41.             )
  42.     )
  43.     private Employee employee;
  45.     public Book() {
  46.     }
  48.     public Book(String bookName, LocalDateTime createdAt) {
  49.         this.bookName = bookName;
  50.         this.createdAt = createdAt;
  51.     }
  53.     public Long getId() {
  54.         return id;
  55.     }
  57.     public void setId(Long id) {
  58.         this.id = id;
  59.     }
  61.     public LocalDateTime getCreatedAt() {
  62.         return createdAt;
  63.     }
  65.     public void setCreatedAt(LocalDateTime createdAt) {
  66.         this.createdAt = createdAt;
  67.     }
  69.     public String getBookName() {
  70.         return bookName;
  71.     }
  73.     public void setBookName(String bookName) {
  74.         this.bookName = bookName;
  75.     }
  77.     public Employee getEmployee() {
  78.         return employee;
  79.     }
  81.     public void setEmployee(Employee employee) {
  82.         this.employee = employee;
  83.     }

课程类别：

  1. @Entity(name = "Course")
  2. @Table(name = "course")
  3. public class Course {
  5.     @Id
  6.     @SequenceGenerator(
  7.             name = "course_sequence",
  8.             sequenceName = "course_sequence",
  9.             allocationSize = 1
  10.     )
  11.     @GeneratedValue(
  12.             strategy = SEQUENCE,
  13.             generator = "course_sequence"
  14.     )
  15.     @Column(
  16.             name = "id",
  17.             updatable = false
  18.     )
  19.     private Long id;
  21.     @Column(
  22.             name = "course_name",
  23.             nullable = false,
  24.             columnDefinition = "TEXT"
  25.     )
  26.     private String courseName;
  28.     @Column(
  29.             name = "department",
  30.             nullable = false,
  31.             columnDefinition = "TEXT"
  32.     )
  33.     private String department;
  35.     @ManyToMany(
  36.             mappedBy = "courses",
  37.             fetch = FetchType.EAGER
  38.     )
  39.     private List<Employee> employees = new ArrayList<>();
  41.     public Course(String courseName, String department) {
  42.         this.courseName = courseName;
  43.         this.department = department;
  44.     }
  46.     public Course() {
  47.     }
  49.     public Long getId() {
  50.         return id;
  51.     }
  53.     public void setId(Long id) {
  54.         this.id = id;
  55.     }
  57.     public String getCourseName() {
  58.         return courseName;
  59.     }
  61.     public void setCourseName(String courseName) {
  62.         this.courseName = courseName;
  63.     }
  65.     public String getDepartment() {
  66.         return department;
  67.     }
  69.     public void setDepartment(String department) {
  70.         this.department = department;
  71.     }
  73.     public List<Employee> getEmployees() {
  74.         return employees;
  75.     }
  77.     public void setEmployees(List<Employee> employees) {
  78.         this.employees = employees;
  79.     }

课程服务：

  1. @Service
  2. public class CourseService {
  4.     private CourseRepository courseRepository;
  6.     @Autowired
  7.     public CourseService(CourseRepository courseRepository) {
  8.         this.courseRepository = courseRepository;
  9.     }
  11.     public void saveCourse(Course course) {
  12.         courseRepository.save(course);
  13.     }
  15.     public void saveAllCourses(List<Course> courses) {
  16.         courseRepository.saveAll(courses);
  17.     }
  19.     public Optional<Course> getCourse (Long id) {
  20.         return courseRepository.findById(id);
  21.     }
  23.     public List<Course> getAllCourses() {
  24.         return courseRepository.findAll();
  25.     }
  27.     public void deleteCourse(Long id) {
  28.         courseRepository.deleteById(id);
  29.     }
  30. }

课程假设：

  1. public interface CourseRepository extends JpaRepository<Course, Long> {
  2. }
JavaspringpostgresqlDatabaseHibernate

1条答案

按热度按时间
gt0wga4j

gt0wga4j1#

我想：

  1. private Set<Employee> employees = new HashSet<>();

也许能解决你的问题。而且在 @ManyToMany 加入尽量不要使用 List<...> 原因列表允许重复，而集合不允许重复元素。

赞(0）分享  回复(0）举报  2021-07-15
我来回答

相关问题

    查看更多

    热门标签

    更多
    JavaquerypythonNode开发语言requestUtil数据库Table后端算法LoggerMessageElementParser

    最新问答

    更多
    • 蜀ICP备13028337号-1 大数据知识库 https://www.saoniuhuo.com © All rights reserved
    • 本站内容来源互联网,如果侵犯您的权益请联系我们删除, 联系方式：448109455@qq.com