having problem with the mailer this post may be duplicated
jakob
----- Original Message -----
From: "Jakob Braeuchi" <[EMAIL PROTECTED]>
To: "OJB Users List" <[EMAIL PROTECTED]>
Sent: Thursday, October 03, 2002 5:36 PM
Subject: Re: Query on collections
> 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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