Hi all,
I have two classes a Fund which has several Prices (historic data over the
last few years).
I also use these objects (in detached mode) as data transfer objects (in the
presentation layer).
Most of the time the whole historic data is not needed but instead only the
current price (the last entry in the
list of prices) is used.
Thus, it is essential to lazily load the prices list. But, I have a problem
to automatically load the currentPrice (I can't get the EntityManager in the
FundListener). I tried something like this:
@Entity
@EntityListeners({FundListener.class})
@NamedQuery(name = "findCurrentPrice", query = "select max(p.date) from
Price p where p.isin = :isin")
public class Fund implements Serializable {
@Transient
private Price currentPrice;
@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy =
"fund")
private List<Price> prices;
}
public class FundListener {
// this doesn't work
@PersistenceContext
private EntityManager manager;
@PostLoad
@PostUpdate
@PostPersist
public void updateCurrentPrice(Fund fund) {
Query q = manager.createNamedQuery("findCurrentPrice");
q.setParameter("isin", fund.getIsin());
fund.setCurrentPrice((Price) q.getSingleResult());
}
}
Of course, I could do something like
fund.getPrices().get(fund.getPrices().size()-1); (without a Query and an
EntityManager) in the updateCurrentPrice method. But when I touch the prices
list, I will cause the prices list to be loaded (in contrast to what I want
with FetchType.LAZY).
I assume that this is a common problem which may have a standard solution.
What am I missing here? How is this problem usually solved?
Any help is greatly appreciated,
Chris
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