problems with association table...

["I. Venuti" <i....@caribel.it>]

Hi,

I have a table (news) where I put some infos. I'd like to associate some 
documents to these news (maybe none). These documents resides in the 
table documents.
I've created an association table called newsdocs, where there are the 
two id's: one for news and one for documents.

The modeler recorgnises the relashionships (infact the object Newsdocs 
has only thwo relationships: toDocuments, toNews.
Also in the object News there is an array (newsdocsArray) and in the 
object Documents (newsdocsArray).

How can I create a relation between a news and a document?

I have tried:

1) created News: nw1 (via createANdRegisterNewObject)
2) created Documents: doc2 (via createANdRegisterNewObject)
3) commit
4) created a black record for Newsdocs:

 Newsdocs ndoc = new Newsdocs();
 ndoc.setDataContext(...) // the same used in (via 
createANdRegisterNewObject)
 ndoc.setToDocuments(doc2); //****** NullPointerException
 ndoc.setToNews(nw1);
 doc2.addToNewsdocsArray(ndoc);
 nw1.add(via createANdRegisterNewObject)

5) commit

Unfortunatly this doesn't work: there is a NullPointerException in ******

Maybe I need to understand better the use of relashionships. Any 
suggestion is wellcome!
Thanks a lot

-- Ivan

Re: problems with association table...

[Malcolm Edgar <ma...@gmail.com>]

Hi Ian,

the NPE is probably due to the object not having a DataContext defined
when you add the related object to it.

regards Malcolm Edgar

On 4/5/06, Cris Daniluk <cr...@gmail.com> wrote:
> There's two ways to do this - if the newsdocs table doesn't have any fields
> at all other than the doc_id and news_id, you don't even need to create an
> ObjEntity for it (you still need a DbEntity though). Just create a flattened
> relationship in the ObjEntity for News that goes to document (documentArray)
> and crosses the newsdoc DbEntity. Create the same in reverse. Then you can
> do:
>
> news.addToDocumentArray(doc);
>
> If you don't want to do this for whatever reason, usually because you have
> other data in the newsdocs table like a sort order, etc, try:
>
> News newsObj = (News) dataContext.createAndRegisterNewObject(News.class);
> Document docObj = (Document) dataContext.createAndRegisterNewObject(
> Document.class);
> NewsDocument newsDocObj = (NewsDocument)
> dataContext.createAndRegisterNewObject(NewsDocument.class);
>
> // set other properties
>
> newsDocObj.setToNews(newsObj);
> newsDocObj.setToDocument(docObj);
>
> dataContext.commitChanges();
>
> Cayenne will automatically resolve the primary keys for you when it commits.
> There is no need to commit twice. By the way, you are asking for trouble
> when you create a DataObject via constructor. Be sure you know what you're
> doing and why when doing that :)
>
> Cris
>
> On 4/5/06, I. Venuti <i....@caribel.it> wrote:
> >
> > Hi,
> >
> > I have a table (news) where I put some infos. I'd like to associate some
> > documents to these news (maybe none). These documents resides in the
> > table documents.
> > I've created an association table called newsdocs, where there are the
> > two id's: one for news and one for documents.
> >
> > The modeler recorgnises the relashionships (infact the object Newsdocs
> > has only thwo relationships: toDocuments, toNews.
> > Also in the object News there is an array (newsdocsArray) and in the
> > object Documents (newsdocsArray).
> >
> > How can I create a relation between a news and a document?
> >
> > I have tried:
> >
> > 1) created News: nw1 (via createANdRegisterNewObject)
> > 2) created Documents: doc2 (via createANdRegisterNewObject)
> > 3) commit
> > 4) created a black record for Newsdocs:
> >
> > Newsdocs ndoc = new Newsdocs();
> > ndoc.setDataContext(...) // the same used in (via
> > createANdRegisterNewObject)
> > ndoc.setToDocuments(doc2); //****** NullPointerException
> > ndoc.setToNews(nw1);
> > doc2.addToNewsdocsArray(ndoc);
> > nw1.add(via createANdRegisterNewObject)
> >
> > 5) commit
> >
> > Unfortunatly this doesn't work: there is a NullPointerException in ******
> >
> > Maybe I need to understand better the use of relashionships. Any
> > suggestion is wellcome!
> > Thanks a lot
> >
> > -- Ivan
> >
> >
>
>

Re: problems with association table...

[Cris Daniluk <cr...@gmail.com>]

There's two ways to do this - if the newsdocs table doesn't have any fields
at all other than the doc_id and news_id, you don't even need to create an
ObjEntity for it (you still need a DbEntity though). Just create a flattened
relationship in the ObjEntity for News that goes to document (documentArray)
and crosses the newsdoc DbEntity. Create the same in reverse. Then you can
do:

news.addToDocumentArray(doc);

If you don't want to do this for whatever reason, usually because you have
other data in the newsdocs table like a sort order, etc, try:

News newsObj = (News) dataContext.createAndRegisterNewObject(News.class);
Document docObj = (Document) dataContext.createAndRegisterNewObject(
Document.class);
NewsDocument newsDocObj = (NewsDocument)
dataContext.createAndRegisterNewObject(NewsDocument.class);

// set other properties

newsDocObj.setToNews(newsObj);
newsDocObj.setToDocument(docObj);

dataContext.commitChanges();

Cayenne will automatically resolve the primary keys for you when it commits.
There is no need to commit twice. By the way, you are asking for trouble
when you create a DataObject via constructor. Be sure you know what you're
doing and why when doing that :)

Cris

On 4/5/06, I. Venuti <i....@caribel.it> wrote:
>
> Hi,
>
> I have a table (news) where I put some infos. I'd like to associate some
> documents to these news (maybe none). These documents resides in the
> table documents.
> I've created an association table called newsdocs, where there are the
> two id's: one for news and one for documents.
>
> The modeler recorgnises the relashionships (infact the object Newsdocs
> has only thwo relationships: toDocuments, toNews.
> Also in the object News there is an array (newsdocsArray) and in the
> object Documents (newsdocsArray).
>
> How can I create a relation between a news and a document?
>
> I have tried:
>
> 1) created News: nw1 (via createANdRegisterNewObject)
> 2) created Documents: doc2 (via createANdRegisterNewObject)
> 3) commit
> 4) created a black record for Newsdocs:
>
> Newsdocs ndoc = new Newsdocs();
> ndoc.setDataContext(...) // the same used in (via
> createANdRegisterNewObject)
> ndoc.setToDocuments(doc2); //****** NullPointerException
> ndoc.setToNews(nw1);
> doc2.addToNewsdocsArray(ndoc);
> nw1.add(via createANdRegisterNewObject)
>
> 5) commit
>
> Unfortunatly this doesn't work: there is a NullPointerException in ******
>
> Maybe I need to understand better the use of relashionships. Any
> suggestion is wellcome!
> Thanks a lot
>
> -- Ivan
>
>