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https://issues.apache.org/jira/browse/CAY-2669?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Nikita Timofeev updated CAY-2669:
---------------------------------
Fix Version/s: 5.0-M2
(was: 5.0-M1)
> Ordering of related entities via relationship definition
> --------------------------------------------------------
>
> Key: CAY-2669
> URL: https://issues.apache.org/jira/browse/CAY-2669
> Project: Cayenne
> Issue Type: Improvement
> Components: Core Library, Modeler
> Affects Versions: 4.1
> Reporter: Stefan S.
> Priority: Major
> Fix For: 5.0-M2
>
> Attachments: Modeler-FR-Ordering-Property-in-Relationship-Dlg.png
>
>
> +*Current Situation:*+
> 'Details' entities are related to their 'master' entities as specified by
> their DB- and object relationships in Cayenne Modeler. When a list of detail
> entities is accessed via according methods of the master object, a query is
> generated according to the defined relationship and executed to resolve the
> details objects.
> For example, the generated query for retrieving all PAINTINGS of an artist is
> something like:
>
> {code:java}
> SELECT t0.id, t0.name, t0.artist_id, t0.gallery_id FROM PAINTINGS t0 WHERE
> t0.artist_id = 999;{code}
>
> +*Feature Request:*+
> It shall be possible, to optionally define the ordering of the details
> entities on DB level (by the query) as attribute of the specific relationship
> by one or more properties of the details entity.
> Cayenne Modeler shall support this relationship attribute (e.g. as additional
> property of the dialog shown below).
>
> This means, that if no ordering is defined, everything stays as is.
> If an ordering is defined, the relationship query of the example above shall
> be generated as
>
> {code:java}
> SELECT t0.id, t0.name, t0.artist_id, t0.gallery_id FROM PAINTINGS t0 WHERE
> t0.artist_id = 999 ORDER BY t0.name ASC;{code}
>
> to order the associated paintings by their name.
> When additional details objects are attached to the master object on Java
> level, the ordering should be maintained, ideally upon the next 'read access'
> to the ordered list property since the order is typically not relevant for
> persisting the list.
> Maintaining the ordering upon modification of the properties relevant for
> ordering is not required, but a programmatic way to restore the defined order
> on Java level is required.
>
> +*Benefit:*+
> Convenience: Currently either 'hacks' or separate queries are required to
> implement this behavior. A built-in solution, esp. when invloving Cayenne
> Modeler, is easier to define and to maintain.
> Performance: If not using a separate query it is currently difficult to
> figure out when the list need to reordered. Separate, explicit queries are a
> significant extra effort for a feature (modelled relationships) that is
> 'almost' available and the optimal (as part of object resolution) execution
> is again not easy to implement (at least without deep knowledge of Cayenne
> internals). The requested feature psuhes sorting of entities onto DB level
> (which is typically performant) and is therefore executed only during entity
> resolution and (lazyly) upon adding additional details object to the list.
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