[jboss-user] [EJB 3.0] - merge one-to-one strategy

[lpiccoli]

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


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