Hi, If you think it's useful, feel free.
As Phil has pointed out, the field-descriptors should be marked as PKs. If you want to flesh it out a little (maybe chuck in the projects class descriptor, or at the least the collection-descriptor), or change it any way - be my guest. Cheers, Charles. >-----Original Message----- >From: Thomas Mahler [mailto:[EMAIL PROTECTED] >Sent: 04 March 2003 19:26 >To: OJB Users List >Subject: Re: Ternary associations > > >Hi Charles, > >thanks for the good explanation and sample (pseudo-) code. >I believed I had to write a testcase with an example, but I >thinks it's >not longer required as your sample gives the whole picture. > >thanks for saving my evening! >Thomas > >PS: If you don't mind I'll place this into our FAQ. > > >Charles Anthony wrote: >> Hi, >> >> OK, I think I understand what you want. >> >> Why is this a "special" scenario ? >> >> You can (and we have in our app) defined a class that represents the >> relationship. We have mapped that to a table with the >corresponding ids. We >> can then do queries/updates on that relationship as with any other. >> >> Here's an example : it's worked entirely in the email and is >probably too >> brief, so it doesn't compile and probably has errors. >However, it should >> illustrate that it is possible with OJB. >> >> java class : >> >> public class ProjectRelationship { >> Integer developerId; >> Integer languageId; >> Integer projectId; >> >> Developer developer; >> Language lanuage; >> Project project; >> /** Normal setters and getters **/ >> } >> >> extract from the repository : >> >> <class-descriptor class="ProjectRelationship" >table="PROJECTRELATIONSHIP"> >> <field-descriptor id="1" name="developerId" column="DEVELOPER_ID" >> jdbc-type="INTEGER" /> >> <field-descriptor id="2" name="languageId" column="LANGUAGE_ID" >> jdbc-type="INTEGER" /> >> <field-descriptor id="3" name="projectId" column="PROJECT_ID" >> jdbc-type="INTEGER" /> >> <reference-descriptor name="developer" class-ref="Developer"> >> <foreignkey field-id-ref="1" /> >> </reference-descriptor> >> <reference-descriptor name="language" class-ref="Language"> >> <foreignkey field-id-ref="2" /> >> </reference-descriptor> >> <reference-descriptor name="project" class-ref="Project"> >> <foreignkey field-id-ref="3" /> >> </reference-descriptor> >> </class-descriptor> >> >> storing a relationship : >> >> Developer d = .... (create or retrieve); >> Project p = .... (create or retrieve); >> Language l = .... (create or retrieve); >> ProjectRelationship r = new ProjectRelationship(); >> r.setDeveloper(dev); >> r.setLanguage(l); >> r.setProject(p); >> >> Broker.store(r); >> >> querying for all relationships that developer 'bob' has in 'java' : >> Criteria criteria = new Criteria(); >> criteria.addEqualTo("developer.name","bob"); >> cirteria.addEquatTo("language.name","java"); >> >> Query q = new QueryByCriteria(ProjectRelationship.class, >criteria, true); >> Collection relationships = Broker.getCollectionByQuery(q); >> >> You can then iterate through the relationships to get the projects. >> >> You could also have on the Project class-descriptor a >> <collection-descriptor> that returns all relationships >associated with the >> Project. If it was call "projectRelationships" the following >would give you >> all projects that have a relationship with "bob" and the >language "java". >> >> Criteria criteria = new Criteria(); >> criteria.addEqualTo("projectRelationships.developer.name","bob"); >> cirteria.addEquatTo("projectRelationships.language.name","java"); >> >> Query q = new QueryByCriteria(Project.class, criteria, true); >> Collection projects = Broker.getCollectionByQuery(q); >> >> Hope that helps , >> >> Cheers, >> >> Charles. >> >> >>>-----Original Message----- >>>From: O'Reilly John [mailto:[EMAIL PROTECTED] >>>Sent: 04 March 2003 16:22 >>>To: 'OJB Users List' >>>Subject: RE: Ternary associations >>> >>> >>>Hi, >>> >>>With a ternary relationship there are three (or more) objects >>>'related' to >>>each other. An example would be 'developer', 'language', >>>'project'. You >>>want to represent the combinations of these that exist. It's >>>realised by a >>>bridge table with 3 columns representing the foreign keys in >>>the other 3 >>>tables (just like an m:n association is represented by a table with 2 >>>columns). >>> >>>The following explains how hibernate supports ternary associations. >>>http://www.xylax.net/hibernate/ternary.html >>> >>>Regards, >>>John >>> >>>-----Original Message----- >>>From: Charles Anthony [mailto:[EMAIL PROTECTED] >>>Sent: 04 March 2003 16:08 >>>To: 'OJB Users List' >>>Subject: RE: Ternary associations >>> >>> >>>I didn't know exactly what a Ternary association is. >>>A quick google suggests that it is what OJB calls an M:N >association (a >>>resolution for a many-many relationship). >>> >>>If it is one of them, then yes, OJB does support it. >>> >>>See >>>http://db.apache.org/ojb/tutorial3.html#mapping%20m:n%20associations >>> >>>Cheers, >>> >>>Charles. >>> >>> >>>>-----Original Message----- >>>>From: O'Reilly John [mailto:[EMAIL PROTECTED] >>>>Sent: 04 March 2003 15:58 >>>>To: 'OJB Users List' >>>>Subject: RE: Ternary associations >>>> >>>> >>>>Hi, >>>> >>>>Sorry to repost the following question but can someone give >>> >>>me a yes/no >>> >>>>answer on this. If no, then we need to look for another way >>>>of doing this. >>>> >>>>Thanks, >>>>John >>>> >>>> >>>>-----Original Message----- >>>>From: O'Reilly John [mailto:[EMAIL PROTECTED] >>>>Sent: 26 February 2003 16:59 >>>>To: 'OJB Users List' >>>>Subject: Ternary associations >>>> >>>> >>>>Hi, >>>> >>>>According to the following, OJB is supposed to support ternary >>>>associations: >>>>http://c2.com/cgi-bin/wiki?ObjectRelationalToolComparison >>>> >>>>I can't find any info on this. Is it actually supported? >>>> >>>>Thanks, >>>>John >>>>*************************************************************** >>>>********* >>>>This e-mail and any files transmitted with it are confidential >>>>and may be >>>>privileged and are intended solely for the individual named/ >>>>for the use of >>>>the individual or entity to whom they are addressed.If you >are not the >>>>intended addressee, you should not disseminate, distribute or >>> >>>copy this >>> >>>>e-mail.Please notify the sender immediately if you have >>>>received this e-mail >>>>by mistake and delete this e-mail from your system.If you >are not the >>>>intended recipient, you are notified that reviewing, >>>>disclosing, copying, >>>>distributing or taking any action in reliance on the contents >>>>of this e-mail >>>>is strictly prohibited.Please note that any views or opinions >>>>expressed in >>>>this e-mail are solely those of the author and do not >>>>necessarily represent >>>>those of Traventec Limited.E-mail transmission cannot be >>>>guaranteed to be >>>>secure or error-free as information could be intercepted, >>>>corrupted, lost, >>>>destroyed, or arrive late or incomplete.Traventec Limited >>>>therefore does not >>>>accept liability for any errors or omissions in the contents of this >>>>message, which arise as a result of e-mail transmission.The >>>>recipient should >>>>check this e-mail and any attachments for the presence of >viruses.This >>>>e-mail has been swept for computer viruses however Traventec >>>>Limited accepts >>>>no liability for any damage caused by any virus transmitted by >>>>this e-mail. >>>> >>>>------------------------------------------------------------ >--------- >>>>To unsubscribe, e-mail: [EMAIL PROTECTED] >>>>For additional commands, e-mail: [EMAIL PROTECTED] >>>>*************************************************************** >>>>********* >>>>This e-mail and any files transmitted with it are confidential >>>>and may be >>>>privileged and are intended solely for the individual named/ >>>>for the use of >>>>the individual or entity to whom they are addressed.If you >are not the >>>>intended addressee, you should not disseminate, distribute or >>> >>>copy this >>> >>>>e-mail.Please notify the sender immediately if you have >>>>received this e-mail >>>>by mistake and delete this e-mail from your system.If you >are not the >>>>intended recipient, you are notified that reviewing, >>>>disclosing, copying, >>>>distributing or taking any action in reliance on the contents >>>>of this e-mail >>>>is strictly prohibited.Please note that any views or opinions >>>>expressed in >>>>this e-mail are solely those of the author and do not >>>>necessarily represent >>>>those of Traventec Limited.E-mail transmission cannot be >>>>guaranteed to be >>>>secure or error-free as information could be intercepted, >>>>corrupted, lost, >>>>destroyed, or arrive late or incomplete.Traventec Limited >>>>therefore does not >>>>accept liability for any errors or omissions in the contents of this >>>>message, which arise as a result of e-mail transmission.The >>>>recipient should >>>>check this e-mail and any attachments for the presence of >viruses.This >>>>e-mail has been swept for computer viruses however Traventec >>>>Limited accepts >>>>no liability for any damage caused by any virus transmitted by >>>>this e-mail. >>>> >>>>------------------------------------------------------------ >--------- >>>>To unsubscribe, e-mail: [EMAIL PROTECTED] >>>>For additional commands, e-mail: [EMAIL PROTECTED] >>>> >>> >>> >>>This email and any attachments are strictly confidential and >>>are intended >>>solely for the addressee. 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