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
>>
>
