问题
In general this back-story does not matter but just to explain the code below:
The server handles users and user groups. User groups are able to "discover" places - at this point in time these places are coming exclusively from the Google Places API.
Current Implementation
Currently, I have a lot of JpaRepository objects, which I call Repository, in my Service Layer. I am stressing "Repository" because in my proposed solution below, they'd be downgraded to DAOs.
However, what I do not like in my current code, and also the reason for my question here, is the amount of repositories one can find in the UserGroupService.
@Service
public class UserGroupService {
private final static Logger LOGGER = LogManager.getLogger(UserGroupService.class);
@Autowired
private UserGroupRepository userGroupRepository;
@Autowired
private UserGroupPlaceRepository userGroupPlaceRepository;
@Autowired
private PlaceRepository placeRepository;
@Autowired
private GooglePlaceRepository googlePlaceRepository;
@Autowired
private GooglePlaces googlePlaces;
public UserGroupService() {
}
@Transactional
public void discoverPlaces(Long groupId) {
final UserGroup userGroup = this.userGroupRepository.findById(groupId).orElse(null);
if (userGroup == null) {
throw new EntityNotFoundException(String.format("User group with id %s not found.", groupId));
}
List<PlacesSearchResult> allPlaces = this.googlePlaces.findPlaces(
userGroup.getLatitude(),
userGroup.getLongitude(),
userGroup.getSearchRadius());
allPlaces.forEach(googlePlaceResult -> {
GooglePlace googlePlace = this.googlePlaceRepository.findByGooglePlaceId(googlePlaceResult.placeId);
if (googlePlace != null) {
return;
}
Place place = new Place();
place.setLatitude(googlePlaceResult.geometry.location.lat);
place.setLongitude(googlePlaceResult.geometry.location.lng);
place.setPlaceType(Place.PlaceType.GOOGLE_PLACE);
place.setName(googlePlaceResult.name);
place.setVicinity(googlePlaceResult.vicinity);
place = this.placeRepository.save(place);
UserGroupPlace.UserGroupPlaceId userGroupPlaceId = new UserGroupPlace.UserGroupPlaceId();
userGroupPlaceId.setUserGroup(userGroup);
userGroupPlaceId.setPlace(place);
UserGroupPlace userGroupPlace = new UserGroupPlace();
userGroupPlace.setUserGroupPlaceId(userGroupPlaceId);
this.userGroupPlaceRepository.save(userGroupPlace);
googlePlace = new GooglePlace();
googlePlace.setPlace(place);
googlePlace.setGooglePlaceId(googlePlaceResult.placeId);
this.googlePlaceRepository.save(googlePlace);
});
}
}
A Solution That Does Not Work
What could make this code a lot simpler and had the potential to resolve this mess up there, would be @Inheritance:
@Entity
@Table(name = "place")
@Inheritance(strategy InheritanceType.JOINED)
public class Place { /* .. */ }
@Entity
@Table(name = "google_place")
public class GooglePlace extends Place { /* .. */ }
However, this is not an option because then I cannot have a PlaceRepository which saves just a place. Hibernate does not seem to like it..
My proposal
I think my confusion starts with the names that Spring is using. E.g. JpaRepository - I am not so sure if this is actually "the right" name. Because as far as I understood, these objects actually work like data access objects (DAOs). I think it should actually look something like this:
public interface PlaceDao extends JpaRepository<Place, Long> {
}
public interface GooglePlaceDao extends JpaRepository<Place, Long> {
}
@Repository
public class GooglePlaceRepository {
@Autowired
private PlaceDao placeDao;
@Autowired
private GooglePlaceDao googlePlaceDao;
public List<GooglePlace> findByGroupId(Long groupId) {
// ..
}
public void save(GooglePlace googlePlace) {
// ..
}
public void saveAll(List<GooglePlace> googlePlaces) {
// ..
}
}
@Service
public class UserGroupService {
@Autowired
private GooglePlaceRepository googlePlaceRepository;
@Autowired
private UserGroupRepository userGroupRepository;
@Transactional
public void discoverPlaces(Long groupId) {
final UserGroup userGroup = this.userGroupRepository.findById(groupId).orElse(null)
.orElseThrow(throw new EntityNotFoundException(String.format("User group with id %s not found.", groupId)));
List<PlacesSearchResult> fetched = this.googlePlaces.findPlaces(
userGroup.getLatitude(),
userGroup.getLongitude(),
userGroup.getSearchRadius());
// Either do the mapping here or let GooglePlaces return
// List<GooglePlace> instead of List<PlacesSearchResult>
List<GooglePlace> places = fetched.stream().map(googlePlaceResult -> {
GooglePlace googlePlace = this.googlePlaceRepository.findByGooglePlaceId(googlePlaceResult.placeId);
if (googlePlace != null) {
return googlePlace;
}
Place place = new Place();
place.setLatitude(googlePlaceResult.geometry.location.lat);
place.setLongitude(googlePlaceResult.geometry.location.lng);
place.setPlaceType(Place.PlaceType.GOOGLE_PLACE);
place.setName(googlePlaceResult.name);
place.setVicinity(googlePlaceResult.vicinity);
googlePlace = new GooglePlace();
googlePlace.setPlace(place);
googlePlace.setGooglePlaceId(googlePlaceResult.placeId);
return googlePlace;
}).collect(Collectors.toList());
this.googlePlaceRepository.saveAll(places);
// Add places to group..
}
}
Summary
I would like to know what I don't see. Am I fighting the framework, or does my data model not make sense and this is why I find myself struggling with this? Or am I still having issues on how the two patterns "Repository" and "DAO" are supposed to be used?
How would one implement this?
回答1:
I would say you are correct that there are too many repository dependencies in your service. Personally, I try to keep the number of @Autowired dependencies to a minimum and I try to use a repository only in one service and expose its higher level functionality via that service. At our company we call that data sovereignty (in German: Datenhoheit) and its purpose is to ensure that there is only one place in the application where those entities are modified.
From what I understand from your code I would introduce a PlacesService which has all the Dependencies to the PlaceRepository, GooglePlaceRepository and GooglePlaces. If you feel like Service is not the right name you could also call it the PlacesDao, mark it with a Spring @Component annotation and inject all the Repositories, which are by definition collections of things
@Component
public class PlacesDao {
@Autowired
private PlaceRepository placeRepository;
@Autowired
private GooglePlaceRepository googlePlaceRepository;
This service/DAO could offer an API findPlacesForGroup(userGroup) and createNewPlace(...) and thus making your for Loop smaller and more elegant.
On a side note: you can merge your first four lines into just one. Java Optionals support a orElseThrow() method:
UserGroup userGroup = userGroupRepository.findById(groupId).orElseThrow(() ->
new EntityNotFoundException(String.format("User group with id %s not found.", groupId));
回答2:
I think the foreach does not look like a good approach to me. You're doing way to much for just a single responsibility of a function. I would refactor this to a standart for loop.
Place place = new Place();
place.setLatitude(googlePlaceResult.geometry.location.lat);
place.setLongitude(googlePlaceResult.geometry.location.lng);
place.setPlaceType(Place.PlaceType.GOOGLE_PLACE);
place.setName(googlePlaceResult.name);
place.setVicinity(googlePlaceResult.vicinity);
place = this.placeRepository.save(place);
This part can easily be a method in a service.
UserGroupPlace.UserGroupPlaceId userGroupPlaceId = new
UserGroupPlace.UserGroupPlaceId();
userGroupPlaceId.setUserGroup(userGroup);
userGroupPlaceId.setPlace(place);
UserGroupPlace userGroupPlace = new UserGroupPlace();
userGroupPlace.setUserGroupPlaceId(userGroupPlaceId);
this.userGroupPlaceRepository.save(userGroupPlace);
That part as well.
googlePlace = new GooglePlace();
googlePlace.setPlace(place);
googlePlace.setGooglePlaceId(googlePlaceResult.placeId);
this.googlePlaceRepository.save(googlePlace);
And this part: I don't understand why your doing this. You could just update the googlePlace instance you loaded from the repo. Hibernate/Transactions are doing the rest for you.
来源：https://stackoverflow.com/questions/49634855/repository-vs-dao-again