服务中的多个 JpaRepository 和多态性

Question

我浏览了互联网，但在使用JpaRepository时无法找到如何处理多态性的方法。
我知道JpaReposity不能将Animal作为类型，因为它不是@Entity 。 我能做的最好的事情是创建一个通用的JpaRepository<T extends Animal, Integer>但它不会帮助我解决多态性问题。
现在，不幸的是，我不得不创建AnimalRepositroy并使用instanceof来定义要使用的存储库，但是有更好的方法吗？

public interface Animal {}

@Entity
...
public class Cat implements Animal {}

@Entity
...
public class Dog implements Animal {}

public interface CatRepo extends JpaRepository<Cat, Integer> {
//...
}

public interface DogRepo extends JpaRepository<Dog, Integer> {
//...
}

@Service
public class MyService {

    private final CatRepo catRepo;
    private final DogRepo dogRepo;

    @Autowired
    public AnimalRepository(CatRepo cr, DogRepo dr) {
        this.catRepo = cr;
        this.dogRepo = dr;
    }

    public Animal save(Animal animal) {
        return animal instanceof Cat ? 
               catRepo.save(animal) : dogRepo.save(animal);
    }

}

Answer 1

我不确定创建某种通用服务/存储库的想法最初是否正确，但是，从技术上讲，您可以执行以下操作：

@NoRepositoryBean
public interface AnimalRepository<A extends Animal> extends JpaRepository<A, Integer> {

    default Class<A> getAnimalType() {
        ResolvableType type = ResolvableType.forClass(getClass()).as(AnimalRepository.class);
        if (!type.hasGenerics()) {
            throw new IllegalStateException();
        }
        Class<?>[] typeArguments = type.resolveGenerics(Object.class);
        if (typeArguments.length < 1) {
            throw new IllegalStateException();
        }
        return (Class<A>) typeArguments[0];
    }

}



public class MyService {

    private List<AnimalRepository<?>> repositories;

    private Map<Class<?>, AnimalRepository<? extends Animal>> repositoryMap = Collections.synchronizedMap(new HashMap<>());

    public MyService(List<AnimalRepository<?>> repositories) {
        this.repositories = repositories;
    }


    protected <A> AnimalRepository<? super A> getRepository(A animal) {
        Class<?> animalClass = animal.getClass();
        AnimalRepository<?> result = repositoryMap.get(animalClass);
        if (result == null) {
            result = doGetRepository(animalClass);
            repositoryMap.put(animalClass, result);
        }
        return (AnimalRepository<? super A>) result;
    }

    protected AnimalRepository<?> doGetRepository(Class<?> animalClass) {
        AnimalRepository<?> result;
        Class<?> cls = animalClass;
        while (cls != null) {
            result = repositoryMap.get(cls);
            if (result != null) {
                return result;
            }
            cls = cls.getSuperclass();
        }
        throw new UnsupportedOperationException("No repository for " + animalClass);
    }

}