hi rudi,
this snippet is from test case QueryTest:
Criteria crit = new Criteria();
crit.addEqualTo("projects.title", "HSQLDB"); // direct m:n
Query q = QueryFactory.newQuery(Person.class, crit);
Collection results = broker.getCollectionByQuery(q);
it's looking for persons working on project named "HSQLDB"
hth
jakob
----- Original Message -----
From: "Rudi Alberda" <[EMAIL PROTECTED]>
To: "OJB Users List" <[EMAIL PROTECTED]>
Sent: Thursday, October 03, 2002 2:44 PM
Subject: Re: Query on collections
> Hey Chris,
>
> Thanks for your tip, but we (and indeed I forgot to mention this) already
do
> the query on m:n
> objects like this (except we use 'hard' table names and PK field names).
> What I was wondering
> was if there was an easier way to do it than like this :)
>
> For example something like this would be extremely cool to have in OJB:
> Criteria c = new Criteria();
> c.addIn("bees[]", B);
> Query q = new QueryByCriteria(B.class, c, false);
> broker.getCollectionByQuery(q);
>
> or even
> Criteria c = new Criteria();
> c.addEqualTo("bees[0].name", B.getName());
> Query q = new QueryByCriteria(B.class, c, false);
> broker.getCollectionByQuery(q);
>
> Nevertheless, thanks for your input! :)
>
>
> ----- Original Message -----
> From: "Chris Lewington" <[EMAIL PROTECTED]>
> To: "OJB Users List" <[EMAIL PROTECTED]>
> Sent: Thursday, October 03, 2002 2:28 PM
> Subject: Re: Query on collections
>
>
> > Hi Rudi,
> >
> > I had to address a similar problem as part of implementing a "query by
> object"
> > mechanism (tricky!) to search on "partially complete" objects rather
than
> using
> > straight queries themselves.. The basic idea I had was as follows:
> >
> > - build an empty A and set your concrete B into its collection (use this
> as a
> > basis for what follows);
> >
> > - use the CollectionDescriptor of class A to get the FK column names of
> the
> > indirection table to both the item class (B) and the "this" class (A),
and
> also
> > the name of the indirection table itself;
> >
> > - then, from your concrete B, use its ClassDescriptor to get the PK
field
> info
> > and hence from that a PersistentField from which you can obtain the
actual
> PK
> > value of your B object;
> >
> > - then build a Criteria object with the following:
> > 1) an "addEqualToColumn" which matches the PK field for A to its
> > corresponding column name in the indirection table, plus
> > 2) an "addEqualTo" which matches the actual PK value you have for B
with
> its
> > corresponding column name in the indirection table;
> >
> > - then finally create a "QueryByMtoNCriteria" with the class of A, the
> > indirection table name and the newly built Criteria object.
> >
> > From there you can do a getCollectionByQuery with your newly built Query
> object
> > above. I'm sure there are easier ways but that was the easiest I could
> come up
> > with for now and it works OK for me.
> >
> > Hope that helps,
> >
> > Cheers,
> >
> >
> > Chris
> >
> > Rudi Alberda wrote:
> >
> > > Hi all,
> > >
> > > I have a question regarding queries on m:n relations. Suppose I have
two
> > > classes which are associated in OJB through a m:n relation, objects of
> type
> > > 'A' and 'B'. 'A' has a property called 'bees' returning all objects of
> type
> > > 'B', 'B' has a property called 'as' which returns all 'A' objects.
> > > This all works nicely in OJB, storing, updating, deleting. But now I
> want to
> > > query. I have an object of type 'B' and I want to know which objects
of
> type
> > > 'A' are associated to it. In other words, I'd like a query which
results
> in
> > > a collection of 'A' objects for which 'B' is in the collection
'A.bees'.
> > > How would this work?
> > > I cannot simply go and create a query like:
> > >
> > > Criteria c = new Criteria();
> > > c.addEqualTo("bees", B);
> > > Query q = new QueryByCriteria(B.class, c, false);
> > > broker.getCollectionByQuery(q);
> > >
> > > because bees is a collection. Will Criteria.addIn work? And if this
> doesn't,
> > > what will?
> > > I have looked at QueryByMtoNCriteria but the documentation of this was
> > > rather unclear.
> > > Also, I might be able to use Criteria.addExists, but I need to refer
to
> a
> > > field from the main query in the subquery, otherwise my subQuery isn't
> of
> > > much use.
> > > Help!
> > >
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> >
>
>
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