Hibernate failed to lazily initialize a collection of role no session in entity service even with @Transactional

Question

I have a hibernate project that connects to two data sources and has a base dao. I use the base dao to derive generic daos for the data sources as well.

I have a service that fetches a join relationship and I am running into the following error when ever an entity has a one to many relationship. I am stuck in that I am not able to get the one to many relationship objects.

I used the apache commons beanutils to copy properties hoping it would do a deep copy but it does not work either. I am running out of ideas.

I read that I there is the option to use Open Session In View but I am not sure how to go about that.

Error

failed to lazily initialize a collection of role: com.sony.spe.mc.domain.OperationalUnit.user, could not initialize proxy - no Session

I have the following layers and files

Controller Layer

    @ApiOperation(value = "read", nickname = "getByID")
    @RequestMapping(value="/read", method = RequestMethod.GET)
    @ApiImplicitParams({
        @ApiImplicitParam(name = "id", value = "User's id", required = true, dataType = "int", paramType = "query")
    })
    @ApiResponses(value = { 
            @ApiResponse(code = 200, message = "Success", response = User.class),
            @ApiResponse(code = 500, message = "Failure")})
    @ResponseBody
    public UserProxy getByID(long id) {
        UserProxy user;
        try {               
            user = userService.fetchUserById(id);
        }
        catch(Exception ex) {
            ex.printStackTrace();
            return null;
        }
        return user;
    }

The Service Layer

User Service

@Service
@Transactional("fuseTransactionManager")
public class UserServiceImpl extends BaseFuseServiceImpl<User> implements UserService {
    @Autowired
    UserDao userDao;

    @Override 
    protected UserDao getDao() {
        return userDao;
    }

    @Override
    public UserProxy fetchUserById(long id) {
        try {
/***** ERROR HAPPENS HERE. THE USER OBJECT IS NOT ABLE TO GET THE ONE TO MANY OBJECTS even though I have @Transactional *****/
            User user = userDao.fetchEntityById(User.class, id);
            UserProxy userProxy = new UserProxy();
            BeanUtils.copyProperties(userProxy, user);
            return userProxy;
        } catch(Exception ex) {
            ex.printStackTrace();
            return null;
        }
    }
.....

Generic Fuse Service

@Service
public class BaseFuseServiceImpl<T extends Serializable> extends BaseServiceImpl<T> implements BaseFuseService<T> {
    @Autowired
    BaseFuseDao<T> baseFuseDao;

    @Override
    protected BaseFuseDao<T> getDao() {
        return baseFuseDao;
    }
}

Very generic service that the specific services implement

@Service
@Transactional("baseTransactionManager")
public abstract class BaseServiceImpl<T extends Serializable> implements BaseService<T> {
    protected abstract BaseDao<T> getDao();

    @Override
    public T fetchEntityById(Class<T> entityClass, long id) {
        return getDao().fetchEntityById(entityClass, id);
    }

User Entity. There is also a corresponding proxy object that is pretty much identical except it does not have the @Entity @Column annotations.

@Entity
@Table(name="USER")
//@AttributeOverride(name = "ID", column = @Column(name = "USER_ID",  nullable = false))
public class User extends BaseEntity {
//public class User implements Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = 5236507646361562577L;

    @Id  
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "USER_ID")
    private long id;  

    @OneToMany(cascade=CascadeType.ALL)  
    @JoinTable(name="USER_OPERATIONALUNIT",  
        joinColumns = {@JoinColumn(name="USER_ID")},  
        inverseJoinColumns = {@JoinColumn(name="OPERATIONALUNIT_ID")}
    )  
    private Set<OperationalUnit> operationalUnit;
.... getters and setters

Answer 1

Why you want make all the methods @Transactional inside class. You can use @Transactional whenever it requires. For best practices use @Transactional over the method.

So in Your case there are 2 solutions:

1.By Fetching childs eagerly:

You need to pass fetchType Eagerly with your annotation i.e.

@OneToMany(cascade=CascadeType.ALL,fetch=FetchType.EAGER)

2. By using @Transactional:

Here you need to initialize you collection in current transaction i.e.

public UserProxy fetchUserById(long id) {
        try {
            User user = userDao.fetchEntityById(User.class, id);
// Here you need to initialize collection using getter method after retrieving object
            user.getOperationalUnit().size();
//Now you will get childs with your parent entity
                UserProxy userProxy = new UserProxy();
                BeanUtils.copyProperties(userProxy, user);
                return userProxy;
            } catch(Exception ex) {
                ex.printStackTrace();
                return null;
            }
        }

For more details about @Transactional Refer this link.