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Re: [eclipselink-users] Odd use case 
Hi Laird,
If I am reading correctly, the relationship between Document and GLaAcounts is not fully represented in the database (the effectiveDate field is not in any table). Is that correct? 

  How are GLAAcounts and Documents inserted into the database?  Are they read-only?
Unless I am mistaken above, I do not think there is anything as simple as what you suggest as a solution. The things that come to mind that might help:
- In JPA you could use named native queries and result set mappings to somehow buildyour objects - EclipseLink allows customization of the queries that are used to traverse mapping. Depending on exactly what you are trying to acheive, you may be able to use a DescriptorCustomizer to access the query that traverses the Document->GlaAccounts mapping and ammend it to accept some additional criteria. 

-Tom

Laird Nelson wrote:
Here's an odd use case that I thought might be food for thought for future releases (or maybe it's already handled). Or it might be such an outlier that I should take my marbles and go home. :-) 

I have a 30 year old schema that I'm mapping to JPA.
There is a particularly odd case where a Document, let's say, conceptually refers to many GLAccounts. But in practical usage terms it only refers to one.
That is, structurally, in the database, a GLAccount has no knowledge of a Document (no foreign key, or implied foreign key, pointing back to it). Similarly, there is no join table setting up a one-or-many-to-many relationship between these two entities.
What there is instead is in the Document table there are 4/5 of a foreign key back to the GLAccount table, whose primary key is defined of 5 components. 

The 5th part of the foreign key is a Date that is supplied from outside.
In JPA terms, what I would like to be able to do is designate a @ManyToOne relationship, but allow the associated @JoinColumns machinery to take in that fifth component from something else (like a @Transient (not transient) property). 

So, hypothetically, in Document:

@Transient
private Date effectiveDate;

@ManyToOne
@JoinColumns(
  @JoinColumn(name = "f1", referencedColumnName = "pk1"),
  @JoinColumn(name = "f2", referencedColumnName = "pk2"),
  @JoinColumn(name = "f3", referencedColumnName = "pk3"),
  @JoinColumn(name = "f4", referencedColumnName = "pk4")
)
*@some.eclipselink.annotation.here.AdditionalJoinCriteria(field = "effectiveDate", referencedColumnName = "pk5")* 
private GLAccount account;
The idea here is that I set the @Transient effectiveDate property, and, since it is @Transient, it does not get mapped to a column. But since it's not Java-language transient, it does get serialized, so it might be available at retrieval time.
With that there, I would hope that I could then simply say getGLAccount() and have the @ManyToOne relationship perform the SELECT query.
Any alternatives to handle this case are appreciated. I obviously know that I can store the four pk components as JPA fields in Document, and then run a query myself; I was hoping for an ability to make this simpler and more transparent. 

THanks,
Laird


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