On Sun, Aug 7, 2016 at 5:13 PM, Jim Hughes <jn...@ccri.com> wrote: > Hi Andrea, > > Thanks for noting the WFS 2.0 joins (I obviously didn't know about > them:)). > > Is the join delegated to the GeoTools DataStore level or does GeoServer > execute queries across the layers? >
Hi Jim, fair question, indeed the join support has some limitations compared to the filter subsystem: - It can be only delegated to the store, there is no in memory execution support - As a consequence, the tables in the join must all reside in the same source, and the filters in the join must be fully encodable - Only "star" joins are supported (single central feature type linking to N others), this is a limitation of the API, Query has a list of Join objects, but a Join cannot have child joins, meaning a "list join" (a join b join c join d) cannot be expressed - Presently, there is no way to say that you want to join N feature types, but only return one (so it's not possible to use joins as a pure filtering mechanism, but only as a tuple building one, the client has to throw away the excess weight after the fact) The store needs to declare support for joins in its query capabilities, so far only the JDBC ones support that. For more details see: https://github.com/geotools/geotools/blob/master/modules/library/api/src/main/java/org/geotools/data/Query.java#L79 https://github.com/geotools/geotools/blob/master/modules/library/api/src/main/java/org/geotools/data/Join.java https://github.com/geotools/geotools/blob/master/modules/library/api/src/main/java/org/geotools/data/QueryCapabilities.java#L112 Of course, resources/funding to improve the join subsystem would be quite welcomed! Cheers Andrea -- == GeoServer Professional Services from the experts! Visit http://goo.gl/it488V for more information. == Ing. Andrea Aime @geowolf Technical Lead GeoSolutions S.A.S. Via di Montramito 3/A 55054 Massarosa (LU) phone: +39 0584 962313 fax: +39 0584 1660272 mob: +39 339 8844549 http://www.geo-solutions.it http://twitter.com/geosolutions_it *AVVERTENZE AI SENSI DEL D.Lgs. 196/2003* Le informazioni contenute in questo messaggio di posta elettronica e/o nel/i file/s allegato/i sono da considerarsi strettamente riservate. Il loro utilizzo è consentito esclusivamente al destinatario del messaggio, per le finalità indicate nel messaggio stesso. Qualora riceviate questo messaggio senza esserne il destinatario, Vi preghiamo cortesemente di darcene notizia via e-mail e di procedere alla distruzione del messaggio stesso, cancellandolo dal Vostro sistema. Conservare il messaggio stesso, divulgarlo anche in parte, distribuirlo ad altri soggetti, copiarlo, od utilizzarlo per finalità diverse, costituisce comportamento contrario ai principi dettati dal D.Lgs. 196/2003. The information in this message and/or attachments, is intended solely for the attention and use of the named addressee(s) and may be confidential or proprietary in nature or covered by the provisions of privacy act (Legislative Decree June, 30 2003, no.196 - Italy's New Data Protection Code).Any use not in accord with its purpose, any disclosure, reproduction, copying, distribution, or either dissemination, either whole or partial, is strictly forbidden except previous formal approval of the named addressee(s). If you are not the intended recipient, please contact immediately the sender by telephone, fax or e-mail and delete the information in this message that has been received in error. The sender does not give any warranty or accept liability as the content, accuracy or completeness of sent messages and accepts no responsibility for changes made after they were sent or for other risks which arise as a result of e-mail transmission, viruses, etc. -------------------------------------------------------
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