Spring LazyInitializatoinException

今天做project创建了一个新的类A，这个新类包含了一个另外一个类B的Set。B类包含了另外一个C类的集合。。。

 public class A{

 @Id

 int id;

 @OneToMany(fetch=FetchType.Lazy)

 Set<B> bInstances;

 public Set<B> getBInstances(){

 return bInstances;

 }

 }

 public class B{

 @Id

 int id;

 @OneToMany(fetch=FetchType.Lazy)

 Set<C> cInstances;

 }

I define a get function with A's aId and B's bId as input parameters in A's facade and it should return B's instance with the exact bId in A's instance with aId.

 @Component
 public class AFacade{
 @Autowired
 AService aService;
 public B getBInstance(int aId, int bId){
      return aService.getBInstance(aId, bId);
 }

 In A's Service class

 @Component
 public class AService{

 @Autowired
 ADao aDao;

 @Transactional
 public A getAInstance(int aId, int bId){
      for(B b: aDao.getAInstance(aId).getBInstances()){
          if( b.getId()==bId){
              return b;
           }
      }
      return null;
 }
 }

With the code above, I always get the LazyInitializationException. Finally, I figure out the reason. The Transaction ends after AService.getAInstance returns. To fix it, I should move the @Transactioanl annotation to the facade class's getBInstance function.