Mapping views with modeller

[Juan José Gil <ma...@gmail.com>]

Hi all, I looked at modeller doc and googled but didn't find out how to map a 
view with cayenne modeler.

Is it possible? 

Or I need to map views manually? In such case, were can I find info on how to 
do this mapping?

Thanks for your time and awesome framework!

Regards,
matero

Re: Re: Mapping views with modeller

[Juan José Gil <ma...@gmail.com>]

Gary, thanks for your aclarations, they cleared mi mind...
after I let my questions out I find some of the answers (like the read-only
objects) myself...
I should learn to do less questions and more reading :(

I expect to return something to cayenne some day :)

regards
Juanjo

2010/7/7 Gary Jarrel <ga...@gmail.com>

> On Wed, Jul 7, 2010 at 11:48 PM, matero <ma...@gmail.com> wrote:
> > Thanks Andrus.
> >
> > So, to map a view, I need to  create it on my DB, then import it with the
> > modeler and then map it.
> > Or I should create the DbEntity as a normal one (putting all its
> attributes as
> > read-only) ?
>
> If you have a view in the database you can reverse engineer it into
> the Cayenne Modeler and the modeler will create both the DB and the
> OBJ entities for you. Alternatively you can do the whole process
> manually by creating a db entity having the same name as your view and
> then map each attribute in the modeler to the respective attribute in
> the view. Then you create your object entity and map it to the
> database entity via the Table/View option and then you can sync the
> object entity so that it picks up all the fields from the view.
>
> > Is it possible from the meta-model maintained by cayenne determine if an
> > ObjEntity maps a table or a view? this could be used to define which
> class
> > extend in the velocity template avoiding update / insert operations.
> > If it is not possible, then I should used some kind of convention on
> > tables/views names but I prefer to use the cayenne meta-model.
>
> Not all views are read only, we commonly use views to update things in
> the database (but not all database would support updating through
> views) however any object entity can me made a "Read Only" entity by
> specifying that it's "Read Only" in the modeler. And in this instance
> the class generator (which uses velocity templates) will not generate
> the setter methods.
>
> > Finally, is there a way to tell the modeler "don't try to assign a PK to
> this
> > kind of entity" (in hibernate there is a "assigned id" strategy whih does
> this).
>
> We tend to include some unique identifier in any given view that we
> use. When we take this approach we set the "PK Generation Strategy" to
> "Database Generated" (in the DB entity) and let the database handle
> the rest.
>
> Otherwise (and I could be wrong here) you can leave out specifying the
> Primary Key in the DB entity and leave the "PK Generation Strategy" at
> default hence nothing would be generated since there is no Primary
> Key. However I don't think this is such a good idea at all.
>
> Hope this helps.
>
> gary
>

Re: Re: Mapping views with modeller

[Gary Jarrel <ga...@gmail.com>]

On Wed, Jul 7, 2010 at 11:48 PM, matero <ma...@gmail.com> wrote:
> Thanks Andrus.
>
> So, to map a view, I need to  create it on my DB, then import it with the
> modeler and then map it.
> Or I should create the DbEntity as a normal one (putting all its attributes as
> read-only) ?

If you have a view in the database you can reverse engineer it into
the Cayenne Modeler and the modeler will create both the DB and the
OBJ entities for you. Alternatively you can do the whole process
manually by creating a db entity having the same name as your view and
then map each attribute in the modeler to the respective attribute in
the view. Then you create your object entity and map it to the
database entity via the Table/View option and then you can sync the
object entity so that it picks up all the fields from the view.

> Is it possible from the meta-model maintained by cayenne determine if an
> ObjEntity maps a table or a view? this could be used to define which class
> extend in the velocity template avoiding update / insert operations.
> If it is not possible, then I should used some kind of convention on
> tables/views names but I prefer to use the cayenne meta-model.

Not all views are read only, we commonly use views to update things in
the database (but not all database would support updating through
views) however any object entity can me made a "Read Only" entity by
specifying that it's "Read Only" in the modeler. And in this instance
the class generator (which uses velocity templates) will not generate
the setter methods.

> Finally, is there a way to tell the modeler "don't try to assign a PK to this
> kind of entity" (in hibernate there is a "assigned id" strategy whih does this).

We tend to include some unique identifier in any given view that we
use. When we take this approach we set the "PK Generation Strategy" to
"Database Generated" (in the DB entity) and let the database handle
the rest.

Otherwise (and I could be wrong here) you can leave out specifying the
Primary Key in the DB entity and leave the "PK Generation Strategy" at
default hence nothing would be generated since there is no Primary
Key. However I don't think this is such a good idea at all.

Hope this helps.

gary

Re: Re: Mapping views with modeller

[matero <ma...@gmail.com>]

Thanks Andrus.

So, to map a view, I need to  create it on my DB, then import it with the
modeler and then map it.
Or I should create the DbEntity as a normal one (putting all its attributes as
read-only) ?

Is it possible from the meta-model maintained by cayenne determine if an
ObjEntity maps a table or a view? this could be used to define which class
extend in the velocity template avoiding update / insert operations.
If it is not possible, then I should used some kind of convention on
tables/views names but I prefer to use the cayenne meta-model.

Finally, is there a way to tell the modeler "don't try to assign a PK to this
kind of entity" (in hibernate there is a "assigned id" strategy whih does this).

Sorry for my poor english and to bother you with this questions.
Thanks in advance.

Regards
matero

Re: Mapping views with modeller

[Andrus Adamchik <an...@objectstyle.org>]

Yes, it is possible. From Cayenne perspective a view is no different  
than a table. So a DbEntity needs to be created for a view, and mapped  
to ObjEntity,

Andrus

On Jul 7, 2010, at 5:01 AM, Juan José Gil wrote:

> Hi all, I looked at modeller doc and googled but didn't find out how  
> to map a
> view with cayenne modeler.
>
> Is it possible?
>
> Or I need to map views manually? In such case, were can I find info  
> on how to
> do this mapping?
>
> Thanks for your time and awesome framework!
>
> Regards,
> matero
>