Trouble persisting one-to-many relationship using jpa in Google app engine - google-app-engine

Question

I have two entities as below and when i try to persist "Category" the "Tip" object list does not get persisted .I noticed that in my DAO class that I was able to see the category object with tipsForCategory list of size 1 but when i try to retrieve after persisting I am able to see only Category details and tipsForCategory comes as empty list.
#Entity
public class Category {
#GeneratedValue
#Id
public Long id;
#Column
public String categoryName;
#OneToMany(mappedBy = "category",cascade = {CascadeType.ALL})
public List<Tip> tipsForCategory;
public Long getId() { return id; }
public String getCategoryName() {
return categoryName;
}
public void setCategoryName(String categoryName) {
this.categoryName = categoryName.toLowerCase();
}
public void addTip(Tip tip) {
if(!tipsForCategory.contains(tip)) {
tipsForCategory.add(tip);
}
}
public List<Tip> getTipsForCategory() {
return tipsForCategory;
}
}
Code for Tip Entity
#Entity
public class Tip {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
public Key key;
#Column
public String tipDescription;
#ManyToOne(cascade = {CascadeType.ALL})
public Category category;
public String getTipDescription() {
return tipDescription;
}
public void setTipDescription(String tipInformation) {
this.tipDescription = tipInformation;
}
}
Code for persisting in my DAO
#Override
#Transactional
public void save(Category category) {
EntityManager localEntityManager=entityManager.getEntityManagerFactory().createEntityManager();
EntityTransaction transaction=localEntityManager.getTransaction();
try {
transaction.begin();
localEntityManager.persist(category);
localEntityManager.flush();
transaction.commit();
}catch (Exception e) {
e.printStackTrace();
localEntityManager.close();
}
}
My retrieval method is
#Override
public CategoryDTO findCategory(Long categoryId) throws FixitException{
CategoryDTO categoryDTO=null;
Category category=categoryDAO.findById(categoryId);
if(category!=null) {
categoryDTO=new CategoryDTO(category);
}
return categoryDTO;
}
#Override
public List<TipDTO> retrieveTips(Long categoryId) throws FixitException{
List<TipDTO> tips=null;
try {
CategoryDTO category = findCategory(categoryId);
if (category != null) {
tips = category.getTipsForCategory();
}
}
catch(Exception e)
{
throw new FixitException(FixitConstants.TIP_RETRIEVAL_ERROR+categoryId,e.getCause());
}
return tips;
}

Answer 1

Looks like the problem was with lazy fetch I just resolved the same.In my categoryDAO.findById(..) code I had to add an additional line to retrieve the tips as below
#Override
public Category findById(Long categoryId) {
Category category=null;
try {
TypedQuery<Category> findByCategoryId = entityManager.createQuery("Select cat from Category cat where cat.id=:categoryId",Category.class);
category=findByCategoryId.setParameter("categoryId", categoryId).getSingleResult();
}
catch (Exception e)
{
e.printStackTrace();
}
*** int tipsSize=category.getTipsForCategory().size();***
return category;
}