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

[Jakob B. <jbr...@ho...>]

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.

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.

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.

jakob




----- Original Message -----
From: "Thomas Mahler" <tho...@ho...>
To: "Jakob Braeuchi" <jbr...@ho...>
Cc: <obj...@li...>
Sent: Friday, May 24, 2002 8:19 PM
Subject: Re: [OJB-developers] problem with path expressions and extents


> Hi Jakob,
>
> I'm not quite sure, but I think this is related to the "buggy" extent
> definition for class Article.
>
> If the InterfaceArticle was used as extent class all would be OK,
> without any changes to Query.
>
> We should setup a new testcase with new persistent classes. The old
> Article ProductGroup stuff is messed up a bit.
>
>
> HTH,
>
> Thomas
>
> Jakob Braeuchi wrote:
>
> > hi all,
> >
> > we have a general problem when using path expression and extents.
> > the following test case reads a cd (an extent of article) and then tries
to
> > read the product group using the relationship 'allArticlesInGroup'
belonging
> > to this cd in a second query. the second query cannot find the
productgroup
> > because 'allArticlesInGroup' refers to Article and not to Cd, so the
> > article-table is used in the join:
> >
> > SELECT A0.Kategorie_Nr,A0.KategorieName,A0.Beschreibung FROM Kategorien
A0
> > INNER JOIN Artikel A1 ON A0.Kategorie_Nr=A1.Kategorie_Nr WHERE
A1.Artikel_Nr
> > = ?
> >
> > the query returning the correct result:
> >
> > SELECT A0.Kategorie_Nr,A0.KategorieName,A0.Beschreibung FROM Cds A0
INNER
> > JOIN Artikel A1 ON A0.Kategorie_Nr=A1.Kategorie_Nr WHERE A1.Artikel_Nr =
?
> >
> > i think we need some kind of hints for path expression, so SqlStatement
> > knows which tables to use.
> > the hints can be set on Criteria or Query level:
> >
> > query.useClass("AllProductsInGroup", Cd.class)
> >
> >
> > Query query;
> > Criteria crit;
> > CdArticle cd;
> > ProductGroup pg;
> >
> > System.out.println("\nread a single cd");
> > crit = new Criteria();
> > crit.addEqualTo("articleId", new Integer(200));
> > query = new QueryByCriteria(CdArticle.class, crit);
> > cd = (CdArticle) broker.getObjectByQuery(query);
> > System.out.println(cd);
> >
> > System.out.println("\nread product group for cd");
> > crit = new Criteria();
> > crit.addEqualTo("allArticlesInGroup.articleId",new
> > Integer(cd.getArticleId()));
> > query = new QueryByCriteria(ProductGroup.class, crit);
> > pg = (ProductGroup) broker.getObjectByQuery(query);
> > System.out.println(pg);
> >
> > this kind of query may look a little exotic in the above sample, but
it's
> > the kind of query used in non decomposed m:n relationship. so we
definitely
> > need a solution here.
> >
> > any help will be appreciated.
> >
>
>
>
>
>
> > jakob
> >
> > _______________________________________________________________
> >
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> >
> >
> >
>
>
>
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>
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>
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