I'm glad somebody finally noticed it. :-)
> On Jan 19, 2017, at 8:29 PM, Andrus Adamchik <and...@objectstyle.org> wrote:
>
> TL;DR: Map relationships dynamically in a running app if you need to connect
> multiple reusable ORM modules.
>
> A longer version:
>
> I'd often mention at various presentations that Cayenne supports generic
> objects and you can create mapping in runtime. I didn't have many real-life
> examples to demonstrate the need until now. But recently I encountered a good
> use case that was solved by dynamic mapping - reusable ORM modules.
>
> Say I have a reusable lib.jar containing a Cayenne project and some
> persistent code built around it. Now I want to use it in app.jar (or app.war
> if you are still on JavaEE). app.jar has its own Cayenne project, with
> entities that need to reference entities in lib.jar. You can't relate them in
> the Modeler, short of unpacking lib.jar and reassembling a new project from
> both projects (the level of effort with such approach would kill most of the
> benefits of reuse).
>
> Consider that in runtime EntityResolver would contain entities from both lib
> and app, so all we need is to connect them. So instead of messing with XML
> files, we'd create a DataChannelFilter in app.jar with "init" method that
> builds all needed relationships on the fly. Now we can access these
> relationships via generic DataObject API (on the app.jar side you can
> optionally create regular type-safe getters and setters). I wrote a utility
> relationship builder that makes this code transparent:
>
> Relationships.oneToOne("libEntity")
> .between(AppEntity.class, LibEntity.class)
> .toDepPK()
> .joined(AppEntity.ID_PK_COLUMN, LibEntity.ID_PK_COLUMN)
> .createReverse("appEntity")
> .exec(resolver);
>
> Needless to say that all this happens in a running application, and is not
> limited to relationships. E.g. you can create flattened attributes instead.
>
> The implications are pretty exciting - you can write fully self-contained
> libraries with Cayenne that can be easily extended (without unpacking) with
> more tables, and otherwise integrated in app DB schemas. Dynamic mapping was
> the last missing piece of a puzzle in a modular CMS design that I am working
> on right now. Ironically the feature was there in Cayenne since Day 1,
> waiting to get noticed.
>
> Andrus
>
> ---------------
> Andrus Adamchik
> @andrus_a | @ApacheCayenne
>
