Grails 2.0.0 is a major step forward for this popular and productive, JVM-based web framework. It has many great new features that make you want to migrate existing projects to this new version.
So I branched our project and started the migration process. Everything went smoothly and I had only to fix some minor compilation problems to get our application running again. Soon the first runtime errors occured and approximately 30 out of over 70 acceptance tests failed. Some analysis showed three major issue categories causing the failures:
- Saving domain objects with belongsTo() associations may fail with a
NULL not allowed for column "AUTHOR_ID"; SQL statement: insert into book (id, version, author_id, name) values (null, ?, ?, ?) [90006-147]message due to grails issue GRAILS-8337. Setting the other direction of the association manually can act as a workaround:book.author.book = book
- When using the MarkupBuilder with the img tag in your TabLibs, your images may disappear. This is due to a new img closure defined in ApplicationTagLib. The correct fix is using
delegate.img
in your MarkupBuilder closures. See GRAILS-8660 for more information.
- Handling of null and the Groovy NullObject seems to be broken in some places. So we got
org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object 'null' with class 'org.codehaus.groovy.runtime.NullObject' to class 'Note'using groovy collections’ find() and casting the result withas:Note myNote = notes?.find {it.title == aTitle} as NoteRemoving type information and the cast may act as a workaround. Unfortunately, we are not able to reproduce this issue in plain groovy and did not have time to extract a small grails example exhibiting the problem.
These bugs and some other changes may make you reconsider the migration of some bigger project at this point in time. Some of them are resolved already so 2.0.1 may be the release to wait for if you are planning a migration. We will keep an open eye on the next releases and try to switch to 2.0.x when our biggest show stoppers are resolved.
Even though I would advise against migrating bigger existing applications to Grails 2.0.0 I would start new projects on this – otherwise great – new platform release.
Schneide Blog 
Thanks for the issue reports. We’re working hard to make sure that 2.0.1 resolves the issues people are encountering on upgrades. We’d be interested in your experiences if you have the time to try 2.0.1 when it’s released.
I can’t reproduce the casting problem in a basic Grails application, so there may be some environmental issue there. A full stack trace may help the Groovy developers pinpoint the underlying cause which may help us to reproduce the problem. Does it only happen in specific artifact types?
After issuing a grails clean we were not able to reproduce the casting problem anymore. So I believe it was just some stale class files hanging around. Sorry for the false positive here.
We will continue to evaluate the upgrade and report any further issues we might face.
Many thanks for your great work and support!