Java 重复的键值违反了唯一约束，但它不应'；t[Spring Boot，PostgreSQL]

代码的简短描述：

用户可以创建一个类别。然后，其他用户可以看到这一点和其他类别。然后，他们可以按类别上的“follow”，然后将其保存到数据库中。下面的图片显示了它在数据库中的外观。到目前为止，一切正常

用户可以创建多个类别，类别只能有一个所有者

类别可以有许多追随者，用户可以跟随许多类别

问题

然而，当用户在另一个类别上按“follow”（使用不同的类别ID和all（请参见下面的HTML和浏览器屏幕截图））时，我的程序崩溃，我得到了这个错误（摘录）：

还表明它在以下位置崩溃：

（这指向控制器中的

userService.updateUser（用户）；

）

尽管调试器和html都显示我正在传递用户\u id=37，类别\u id=6。

然而如果我停止我的IDE并再次启动它（DB仍然显示first follow，如图中所示），然后我使用同一用户（同一用户id）登录并在另一个类别上按follow，则一切正常，数据库更新（见下图）

然后，若我尝试遵循另一个类别，同样的崩溃再次发生，我将不得不重新启动IDE使其再次工作

目标

用户应该能够跟踪多个类别而不会发生崩溃

我尝试过的内容（没有任何帮助）：

我尝试在用户类中添加

cascade={CascadeType.PERSIST，CascadeType.MERGE}

重写两个实体类中的Equals和Hashcode

实体

• 使用者

服务

• 用户服务

• 分类服务

存储库

• 用户存储库

@存储库
公共接口用户存储库扩展了JpaRepository{
可选findUserByUsername（字符串用户名）；
}

• 类别存储库

@存储库
公共接口类别repository扩展了JpaRepository{
}

相关HTML代码（带thymeleaf）

类别：

跟随

它在浏览器中的外观：

DB如何处理以下问题

DB如何关注一次、重新启动IDE，然后关注另一个类别

---

问题很可能是您没有为

类别

实现equals/hashCode，因此将其添加到集合将添加一个副本，然后尝试将其保留。

（编辑）解决了：

找到了实际的答案和解决方案：

不需要从控制器传递用户，而需要从存储库通过其id获取用户

2020-10-09 20:12:21.526  WARN 25512 --- [io-8080-exec-10] o.h.engine.jdbc.spi.SqlExceptionHelper   : SQL Error: 0, SQLState: 23505
2020-10-09 20:12:21.526 ERROR 25512 --- [io-8080-exec-10] o.h.engine.jdbc.spi.SqlExceptionHelper   : ERROR: duplicate key value violates unique constraint "followed_categories_pkey"
  Detail: Key (user_id, category_id)=(37, 5) already exists.
2020-10-09 20:12:21.526  INFO 25512 --- [io-8080-exec-10] o.h.e.j.b.internal.AbstractBatchImpl     : HHH000010: On release of batch it still contained JDBC statements
2020-10-09 20:12:21.529 ERROR 25512 --- [io-8080-exec-10] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.dao.DataIntegrityViolationException: could not execute statement; SQL [n/a]; constraint [followed_categories_pkey]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement] with root cause

org.postgresql.util.PSQLException: ERROR: duplicate key value violates unique constraint "followed_categories_pkey"
  Detail: Key (user_id, category_id)=(37, 5) already exists.

at com.blog.reviewwebsite.controller.CategoryController.followCategory(CategoryController.java:59) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_252]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_252]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_252]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_252]

@Getter
@Setter
@Entity
@Table(name = "users")
public class User implements UserDetails {

    //other fields

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "user_id")
    private Long id;

    //This one is used when a user makes a new category
    @OneToMany(mappedBy = "user", fetch = FetchType.LAZY)
    private Set<Category> categories;


    //This one is used when a user follows existing category
    @ManyToMany(fetch = FetchType.EAGER)
    @JoinTable(
            name = "followedCategories",
            joinColumns = @JoinColumn(name = "user_id"),
            inverseJoinColumns = @JoinColumn(name = "category_id")
    )
    private Set<Category> followedCategories = new HashSet<Category>();
}

@Entity
@Getter
@Setter
@Table(name = "Category")
public class Category {

    //other fields

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "category_id")
    private Long id;

    //This one is used when a user makes a new category
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "id", nullable = false)
    private User user;

    //This one is used when a user follows existing category
    @ManyToMany(mappedBy = "followedCategories")
    private Set<User> users;
}

@Controller
@RequestMapping("/categories")
public class CategoryController {

    private CategoryService categoryService;
    private UserService userService;

    public CategoryController(CategoryService categoryService, UserService userService) {
        this.categoryService = categoryService;
        this.userService = userService;
    }

    //other methods

    @PostMapping("/follow/{id}")
    public String followCategory(@PathVariable Long id, @AuthenticationPrincipal User user) {
        Category category = categoryService.getOneById(id);
        user.getFollowedCategories().add(category);
        userService.updateUser(user);

        return "redirect:/categories/all";
    }
}

@Service
public class UserService implements UserDetailsService {

    private UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    //other methods

 public User updateUser(User user) {
        return userRepository.save(user);
    }
}

@Service
public class CategoryService {

    private CategoryRepository categoryRepository;

    public CategoryService(CategoryRepository categoryRepository) {
        this.categoryRepository = categoryRepository;
    }

    //other methods

    public Category getOneById(Long id) {
        return categoryRepository.getOne(id);
    }
}

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
    Optional<User> findUserByUsername(String username);
}

@Repository
public interface CategoryRepository extends JpaRepository<Category, Long> {
}

<div th:each="category: ${categories}">


    <p> Category:
        <span><a th:href="@{/reviews/(categoryId=${category.id})}" th:text="${category.name}"></a>
        <span th:text="${category.user.username}"></span>
        <span th:text="${category.id}"></span>
        </span>
    </p>
    <form method="post" th:action="@{/categories/follow/{id}/(id=${category.id})}">
        <span>follow</span>
        <input type="submit">
    </form>

</div>