Thanks! Now I have something fun to work on during the weekend :) - hugi
> On 20. jan. 2017, at 14:26, Andrus Adamchik <and...@objectstyle.org> wrote: > > Here it is: > > https://gist.github.com/andrus/29616d6f20fc5094a4eb77114d751db0 > > Hides lots of verbosity in Cayenne mapping API. We may port it to Cayenne in > the future releases if we are to pursue the topic of dynamic mapping. > > Andrus > >> On Jan 20, 2017, at 8:24 AM, Hugi Thordarson <h...@karlmenn.is> wrote: >> >> As someone who uses multiple Cayenne projects in separate jars a lot (I have >> a project for db documentation, another one for user management, another one >> for generic object tagging etc. etc.) this is quite awesome and I have >> oodles of use cases. Can you share the code for the Relationships utility >> class? >> >> Allowing the Modeler to load and handle multiple models simultaneously would >> also be very nice, but that’s a whole another story… >> >> - hugi >> >> >>> On 20. jan. 2017, at 01:29, 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 >>> >> >
