Re: [OJB-developers] problem with path expressions and extents

[Thomas M. <tho...@ho...>]

Hi Jakob,

Jakob Braeuchi wrote:

 > hi thomas,
 >
 > unfortunately it's not related to buggy extent definition, it's a general
 > problem !!!
 >



:-(


 > when the SqlStatement resolves the path expressions ie:
 > 'allArticlesInGroup.id' then it looks up the collection descriptor for
 > 'allArticlesInGroup' in the class definition of productgroup.
 > this collection descriptor references the base class only ( Article ), so
 > SqlStatement will use the table of the base class for the query and thus
 > will not find a productgroup for the CdArticle with id 200.
 >


Oh, now I got it! That's really a problem.


 > i implemented a kind of hint for SqlStatement:
 > QueryByCriteria#addPathClass(aPathSegment, aClass)
 >
 > ie: addPathClass("allArticlesInGroup", CdArticle.class), so SqlStatement
 > will use the table for CdArticle when building the sql.
 >


OK!


 > this stuff is now in cvs, and there's also a testcase for it:
 > QueryTest#testInversePathExpression().
 > so far it's used only for querying inverse m:n relationships in
 > PersistenceBrokerImpl##getMtoNQuery().
 >
 > an other cleaner solution would be the use of sql UNION whenever dealing
 > with extents, but mysql currently does not support them.
 >

Yes UNION statements are not supported on some platforms and on other
platforms they are quite slow.
So I think using a hin for this kind of lookups is OK.

cheers,

Thomas