当我认为我可以从 Spring 中的实体访问服务时，替换我的代码的更好解决方案是什么？

Question

I have a problem to access service in my entity. I know, besides my code doesn't work, it's also not recomended. So, i want to know what is the best practice if i have the problem like this? Here are my class.

The Controller Class:

@Controller
@RequestMapping("step")
public class TenderController {
   @Autowired
   StepService stepService;

   @GetMapping("")
   public ModelAndView index(ModelAndView mView,
                          @ModelAttribute(name = "result_code") String result_code,
                          @ModelAttribute(name = "result_message") String result_message) {
   mView.addObject("stepList", stepService.getAllSteps());
   mView.setViewName("pages/step/index");
   return mView;
   }
}

On my view html, I iterate the stepList

<tr th:each="s:${stepList}" 
    th:classappend="${s?.isStepNow()?'bg-success':''}">
    <!-- some td --> 
</tr>

The problem is, for some reason, i have to use if else condition to get the current date to use in isStepNow() method. One from operating system. The other one from the database. So, i come up with an idea to create a service class

Here are the Service Class :

public interface TimeServices {
   Date getNow();
}

and The Implementation Class:

@Service
public class TimeServicesImpl implements TimeServices {
  @Value("${app.mode}")
  String appMode;

  @Autowired
  DateDBRepository dateDBRepository;

  @Override
  public Date getNow() {
    if(appMode.equalsIgnoreCase("GET_FROM_DB")){
        Optional<DateDB> dateDBOptional =  dateDBRepository.findById(1L);
        if(dateDBOptional.isPresent()){
            return dateDBOptional.get().getDate();
        }else{
            throw new IdNotExistsException();
        }
    }else{
        return new Date();
    }
 }

}

The Problem is in my Entity:

@Entity
@Table(name = "step")
public class Step{

   @Autowired
   @Transient
   TimeServices timeServices; //BAD PRACTICE AND DOESN'T WORK

   @Id
   @GeneratedValue(strategy = GenerationType.IDENTITY)
   private Long id;

   private Date start;
   private Date end;

   public Boolean isStepNow(){
      Date now = timeServices.getNow(); //THE PROBLEM
      if(now.compareTo(start)>0 && end.compareTo(now)>0) {
         return true;
      }else{
         return false;
      }
   }
}

Of course it doesn't work, because the timeService is always null. Anyone have some recommendation for me to solve this problem?

I know i can edit my isStepNow() to isStepNow(Date date). Then, i can access the service via controller. So i can call the isStepNow(date) on my view. But, i think it's not efficient in writing source code because i have to access the service from some controllers rather than only write it one time in the entity.

Answer 1

I've seen this discussion a lot. People using DDD tend to solve it as follows:

• Rename your @Entity-annotated class to StepEntity or ORMStep something similar, and only keep the fields needed to do ORM in that class.
• Create a different (domain) class Step that you create using a ORMStep and dependent services, and put your domain logic methods in that class.
• Let the StepService interface (better call it StepRepository) return Step class, not ORMStep.
• Implement the StepRepository by injecting both the DAO (which Spring Data confusingly also calls Repository) and the dependent services, and combine them to read ORMSteps and convert to Step classes.

This seems like a lot of effort, and you probably need to convert the Step instances back to ORMStep classes too to do updates, but in the long run it's a very clean solution. You can evolve the Step classes independently of the ORM classes or switch the ORM without having to change the controller etc.

It's also TDD-friendly, since all business logic is in the domain objects, not in the ORM objects, so you can unit test them much easier.

If the classes you use have a lot of fields, MapStruct and/or Lombok Builders can keep your code cleaner.