hi all,

I am having troubles understanding the EJB3 updating strategy. I am familar with the traditional mechanism of dealing with just FK when updating a one-to-one relationship. However with EJB3 the FK is now a object.
From the EJB3trail there is a example that does the following for a persist.
It loads both foreign key objects before setting, then persisting.

public double calculate (int fundId, int investorId, double saving) {
26
27 Investor investor =
28 em.find(Investor.class,
29 Integer.valueOf(investorId));
30 Fund fund =
31 em.find(Fund.class,
32 Integer.valueOf(fundId));
33
34 int start = investor.getStartAge();
35 int end = investor.getEndAge();
36 double growthrate = fund.getGrowthrate();
37
38 double tmp = Math.pow(1. + growthrate / 12., 12. * (end - start) + 1);
39 double result = saving * 12. * (tmp - 1) / growthrate;
40 Timestamp ts = new Timestamp (System.currentTimeMillis());
41
42 TimedRecord rec =
43 new TimedRecord (fund, investor, saving, result, ts);
44 em.persist (rec);
45
46 return result;
47 }

Is the same mechanism required when updating?
Unfortunetly the EJB3trail does not have a one-to-one merge example.
Is something like the following performant or are there better mechanisms?
The major issue is executing the load of the FK relationship object. Which seems expensive when i already have the FK id.

strategy 1

public double update (int recId, int fundId, int investorId, double saving) {

 Investor investor =
 em.find(Investor.class,
 Integer.valueOf(investorId));
 Fund fund =
 em.find(Fund.class,
 Integer.valueOf(fundId));
 TimeRecord rec =
 em.find(Fund.class,
 Integer.valueOf(fundId));

 rec.setSaving( saving);
 rec.setFund( fund );
 rec.setInvestor( investor );
 em.merge (rec);

 return result;
 }

I have tried the following with little success as it complains about transient Objects

strategy 2 not working.

public double update2 (int recId, int fundId, int investorId, double saving) {

 Investor investor =new Investor( investorId);
 Fund fund = new Fund( fundId);
 TimeRecord rec =
 em.find(Fund.class,
 Integer.valueOf(fundId));

 rec.setSaving( saving);
 rec.setFund( fund );
 rec.setInvestor( investor );
 em.merge (rec);

 return result;
 }

So my question is does the merge on one-to-one relationship require fullly populated detached objects or can it be done with just the id for the FK?

many thanks

-lp