双向@OneToMany/@ManyToOne关系级联

Question

我在将带有@ManyToOne关系的实体(雇员)映射到带有@OneToMany关系的实体(社区)时遇到了问题。

当我将一个实体（社区）分配给一个实体（员工），其中社区的值为空时，它工作正常。

问题出现了，如果雇员已经为社区分配了价值。当我更改该值并保存更改时，该员工为社区获得了新的值，并且这个新社区在集合中获得了该员工。唯一的问题是，老社区仍然有这个员工在收集，但它应该被删除。这只有在数据库重新启动时才会发生。

我试图使用@JoinCol列和@JoinTable来解决这个问题，但问题是一样的。我想通过在更新/创建服务方法中调用JPA来避免从旧关系中删除实体。

这个问题有什么解决办法吗？

以下是代码：

>

一个社区

 @Entity
 @Table(name = "community")
 public class Community implements Serializable {

 private static final long serialVersionUID = 1L;

 @Id
 @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "sequenceGenerator")
 @SequenceGenerator(name = "sequenceGenerator")
 @Column(name = "id")
 private Long id;

 @OneToMany(mappedBy = "community", orphanRemoval = true, cascade = CascadeType.ALL)
 private Set<Employee> employees = new java.util.LinkedHashSet<>();

 public Long getId() {
     return this.id;
 }

 public Community id(Long id) {
     this.setId(id);
     return this;
 }

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

 public Set<Employee> getEmployees() {
     return this.employees;
 }

 public void setEmployees(Set<Employee> employees) {
     if (this.employees != null) {
         this.employees.forEach(i -> i.setCommunity(null));
     }
     if (employees != null) {
         employees.forEach(i -> i.setCommunity(this));
     }
     this.employees = employees;
 }

 public Community employees(Set<Employee> employees) {
     this.setEmployees(employees);
     return this;
 }

 public Community addEmployees(Employee employee) {
     this.employees.add(employee);
     employee.setCommunity(this);
     return this;
 }

 public Community removeEmployees(Employee employee) {
     this.employees.remove(employee);
     employee.setCommunity(null);
     return this;
 }

一个雇员。

  @Entity
  @Table(name = "employee")
  public class Employee implements Serializable {

  private static final long serialVersionUID = 1L;

  @Id
  @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "sequenceGenerator")
  @SequenceGenerator(name = "sequenceGenerator")
  @Column(name = "id")
  private Long id;

  @ManyToOne(optional = false)
  @JoinColumn(name = "community_id")
  //    @JoinTable(name = "rel_community__employees",
  //        joinColumns = {@JoinColumn(name = "community_id", referencedColumnName = 
            "id", nullable = false)},
  //        inverseJoinColumns = {@JoinColumn(name = "employee_id", 
            referencedColumnName = "id", nullable = false)})
  @Cascade({CascadeType.PERSIST, CascadeType.REFRESH)
  private Community community;

  public Long getId() {
      return this.id;
  }

  public Employee id(Long id) {
      this.setId(id);
      return this;
  }

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

  public Community getCommunity() {
      return this.community;
  }

  public void setCommunity(Community community) {
      this.community = community;
  }

  public Employee community(Community community) {
      this.setCommunity(community);
      return this;
  }

管理{@link Employee}的服务实现。

  @Service
  @Transactional
  public class EmployeeServiceImpl implements EmployeeService {

  @Override
  public EmployeeDTO save(EmployeeDTO employeeDTO) {
      Employee employee = employeeMapper.toEntity(employeeDTO);
      employee = employeeRepository.save(employee);
      return employeeMapper.toDto(employee);
  }

  @Override
  public EmployeeDTO update(EmployeeDTO employeeDTO) {
      Employee employee = employeeMapper.toEntity(employeeDTO);
      employee = employeeRepository.save(employee);
      return employeeMapper.toDto(employee);
  }

}

Answer 1

这仅在数据库重新启动时发生。

您是否确定一个社区集合中的员工与另一个社区中的员工相同（即具有相同的id）？我猜您可能有重复的Employee对象。

你的代码在我看来很好，所以这应该像你预期的那样工作。

如果没有重复的< code>Employee行，另一种可能的解释是您之前的更新没有正确提交到数据库(您的数据库丢失了数据)。< code>Employee对< code>Community集合的成员资格是通过表< code>employee中的FK community_id定义的，因此，如果您在< code>Community的集合中发现一个不属于它的< code>Employee，这意味着FK值没有正确更新，或者更新它的事务没有正确提交。

所以，现在你必须弄清楚那里到底发生了什么。我的猜测是，由于某些原因，FK没有正确更新。