如何使 Spring Data Rest 参考相同的实体类型工作？

Question

我有这个实体：

@Entity
@Data
@NoArgsConstructor
@Table(name = "employees")
public class Employee {

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

    private String firstName;

    private String lastName;

    @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.PERSIST)
    @JoinColumn(name = "manager_id")
    private Employee manager;
}

有对应的仓库：

public interface EmployeeRepository extends JpaRepository<Employee, Long> {
    // ..
}

当我发出GET 请求以通过id 查找员工时，我得到以下结果：

{
   "firstName":"Steven",
   "lastName":"King",
   "_links":{
      "self":{
         "href":"http://localhost:8081/api/employees/100"
      },
      "employee":{
         "href":"http://localhost:8081/api/employees/100"
      },
      "manager":{
         "href":"http://localhost:8081/api/employees/100/manager"
      }
   }
}

http://localhost:8081/api/employees/100/manager 不能与 Lazy fetching 一起使用，那么我该如何将其更改为：http://localhost:8081/api/employees/99 其中 99 是 @ 987654329@史蒂文的经理？

Answer 1

根据Spring Data REST Reference，可以定义RepresentationModelProcessor<EntityModel<T>>类型的bean，在序列化T类型的实体时，Spring Data REST会自动拾取。

你可以自己在那里建立一个EntityModel。

@Component
public class EmployeeModelProcessor implements RepresentationModelProcessor<EntityModel<Employee>> {

    private final RepositoryEntityLinks entityLinks;

    public EmployeeModelProcessor(RepositoryEntityLinks entityLinks) {
        this.entityLinks = entityLinks;
    }

    @Override
    public EntityModel<Employee> process(EntityModel<Employee> employeeModel) {

        Employee employee = employeeModel.getContent();

        EntityModel<Employee> newEmployeeModel = EntityModel.of(employee);
        newEmployeeModel.add(employeeModel.getRequiredLink(IanaLinkRelations.SELF));
        newEmployeeModel.add(employeeModel.getRequiredLink("employee"));

        if (null != employee.getManager()) {
            newEmployeeModel.add(entityLinks.linkToItemResource(Employee.class, employee.getManager().getId()).withRel("manager"));
        }

        return newEmployeeModel;
    }

}

您可以找到有关 RepositoryEntityLinks here 的文档。

那么响应JSON应该变成

{
   "firstName":"Steven",
   "lastName":"King",
   "_links":{
      "self":{
         "href":"http://localhost:8081/api/employees/100"
      },
      "employee":{
         "href":"http://localhost:8081/api/employees/100"
      },
      "manager":{
         "href":"http://localhost:8081/api/employees/99"
      }
   }
}