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How to setup one-to-many unidirectional mapping for grails application on GAE ?

Answer 1

A:

Looks like the problem is that you don't have a User on the Role since you'll need to specify the mappedBy on the collection I think.

@OneToMany(mappedBy="user",fetch=FetchType.EAGER)
Set<Role> roles

Also you don't really need the join table stuff since you aren't really working with tables in app-engine. In essence the role will exist under the user entity.

Hope that helps :)

Philip Dodds 2009-09-04 04:37:28

oh and remember to add a user field to the Role class

Philip Dodds 2009-09-04 04:38:20

Thanks for fast response and helpful advice. I try with your advice by refer to http://www.java2s.com/Code/Java/JPA/OneToManyMappingWithMappedByToremoveMappingTable.htmBut I face error below while access to role/list page.Error Cause:org.datanucleus.exceptions.NucleusUserException: Field com.vobject.grailsfuse.Role.user should be able to provide a reference to its parent but the entity does not have a parent. Did you perhaps try to establish an instance of com.vobject.grailsfuse.Role as the child of an instance of com.vobject.grailsfuse.User after the child had already been persisted?

limcheekin 2009-09-05 09:19:37

The latest source code located at:http://rapidshare.com/files/275893205/one2many.zip.html

limcheekin 2009-09-05 09:41:07

Answer 2

A:

FYI, I had managed to implement one-to-many relationship using "Unowned One-to-Many Relationships", please refer to http://code.google.com/appengine/docs/java/datastore/relationships.html#Unowned%5FRelationships for more information.

Thanks for kindly help so far.

limcheekin 2009-09-12 09:29:31

Answer 3

A:

Dear Philip,

I had implemented the outcome above and stark security into a project called grailsfuse that intended to run on google appengine with custom authentication.

You can access the application at URL below:
grailsfuse.appspot.com

The code is developed using App Engine SDK 1.2.5. You can access the URL below for complete source code:
https://vobject.svn.sourceforge.net/svnroot/vobject/grails/grailsfuse/trunk

Plugins used:
app-engine 0.8.3, gorm-jpa 0.5, stark-security 0.4.2

Please take note that after you install gorm-jpa plugin to the project, you need to apply the fix of URL below to ensure the login screen is working properly:
jira.codehaus.org/browse/GRAILSPLUGINS-1366

Working features:
Unowned One-to-Many Relationships between User and Role

Outstanding Issue:
While execute in app-engine, unable to access to appropriate URL (included /index.gsp, **/create, **/update, **/delete, etc) even after login successfully, suspect something wrong with URL redirection.

Any idea for the outstanding issues above?

Thanks.

limcheekin 2009-09-12 10:27:50

Answer 4

A:

Hi,

For the update, I released appengine-gorm plugin to grails plugin repository, the motivation I wrote this plugin to support batch insert operation. As I am unable to make the one-to-many relationship by using annotation (@OneToMany) working in Google App Engine after so many attempts, I decided to manage the relationship manually instead of using the mapping. However, while I attempt to save the objects in the many side of the one-to-many relationship, I am facing request timeout of google app engine. Then, I find out that the low level API of datastore support persist many objects in one API call, so there is the born of this plugin. Hopefully, it is benefit you and others.

Lastly, I managed make the one-to-many relationship working manually and without the mapping. Please look at live demo app called GrailsFuse at http://grailsfuse.vobject.com/.

I welcome your feedback and comments. Please feel free to drop me an email at limcheekin at vobject dot com.

Thanks.

limcheekin 2009-11-30 03:26:21

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How to setup one-to-many unidirectional mapping for grails application on GAE ?

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