You could always break a join across two (or more) data nodes into separate queries, each feeding the next one. It would be cool if SelectQuery did that automatically, but it's certainly not a show stopper.
/dev/mrg
-----Original Message-----
From: Andrus Adamchik [mailto:andru..bjectstyle.org]
Sent: Tuesday, February 15, 2005 1:04 PM
To: cayenne-use..bjectstyle.org
Subject: Re: Multiple DataNodes
If you search the archives, you may find some older discussions on the
topic. I know of one limitation that was identified back then - queries
that have to make joins across DataNodes will not work (it also means that
regular relationships will work fine).
E.g. (taking our artist/painting example, assuming Artist and Painting
tables coming fro different DBs):
// relationships will work
artist.getPaintings();
painting.getArtist();
// one step qualifiers will work
new SelectQuery(Painting.class, Expression.fromString("artist = ..));
// *** multi-step qualifiers will break as they are translated to a join
new SelectQuery(Painting.class, Expression.fromString("artist.name = 'a'"));
Andrus
> Good news. Never did such a thing, so I was a bit worried.
>
> Thanks Michael.
>
>
> On Tue, 15 Feb 2005 11:28:12 -0500, Gentry, Michael (Contractor)
> <michael_gentr..anniemae.com> wrote:
>> I have a utility/admin application which uses multiple data nodes and
>> I didn't really do anything special. Cayenne knows which DataNode
>> (and therefore DB connection) to use by which DataDomain your
>> DataContext is connected to and which Java classes (CayenneDataObject)
>> you are using. So if you have a User in one DataNode and an Invoice
>> in another, Cayenne will handle that just fine.
>> Selects/inserts/updates/deletes will occur across the different
>> connections and I believe (never tried it) that relationships across
>> the different DBs will work fine, too.
>>
>> /dev/mrg
>>
>>
>> -----Original Message-----
>> From: Joćo Paulo Vasconcellos [mailto:vasconcello..mail.com]
>> Sent: Tuesday, February 15, 2005 11:18 AM
>> To: cayenne-use..bjectstyle.org
>> Subject: Multiple DataNodes
>>
>> Hello list,
>>
>> I'm working with a legacy system that has information spread across
>> 3 databases. My Apllication needs to access the 3 dataNodes. In the
>> modeler, I created the 3 nodes, 3 maps and inported the db schema.
>>
>> My question is: Do I need any special treatment to work with 3
>> different dataNodes? If so, what should I be aware of? Is there some
>> placece in the docs where I can find it, aside from the customer ASP
>> example (because I think this is a different setup)?
>>
>> Thanks,
>> --
>> Joćo Paulo Vasconcellos
>> ICQ: 123-953-864
>>
>
>
> --
> Joćo Paulo Vasconcellos
> ICQ: 123-953-864
This archive was generated by hypermail 2.0.0 : Tue Feb 15 2005 - 15:35:38 EST