I've got several apps that use the same Hibernate domain classes and mappings so they're in a jar file.

I've used them in a Grails app by copying my existing hibernate.cfg.xml into grails-app/conf/hibernate. Hibernate seems to find the mapping files in the jar with no trouble.

How can we use named queries declared in mapping files? I have couple of them and i'm finding difficulty in executing them the same way as specified in GRAIL documentation.

http://grails.org/doc/latest/ref/Domain Classes/namedQueries.html

Thanks

Thanks Peter.

I did find that out. I should have posted earlier. I went the same route as you have mentioned.

Also do you need package name in your constraints script?

I had hibernate mapping files and wrote the domain classes in groovy. I had to place them in src/groovy and not in the domain directory because otherwise I got "Duplicate entity.." exception.
With scaffolding enabled in the controller, when I access the web pages, the List works fine but the Create page does not show my Id field – even if the generator is 'assigned'.
The Edit page cannot be displayed – shows error "No such property: version".
So, can scaffolding be used in such cases?

What about Java domain objects mapped using hibernate? I tried that too. These objects are accessible and fine if I use them using the session (from injected sessionFactory)but the scaffolding does not work on these.
I get the following error/exception if I set scaffolding to my Java class.

2011-03-04 15:57:26,077 [http-8080-1] ERROR view.ScaffoldingViewResolver – Erro
r generating scaffolded view [/sample/list]: null
java.lang.NullPointerException
at java.lang.Class.isAssignableFrom(Native Method)
at java_lang_Class$isAssignableFrom.call(Unknown Source)
at SimpleTemplateScript2$_run_closure1.doCall(SimpleTemplateScript2.groo
vy:29)
at SimpleTemplateScript2.run(SimpleTemplateScript2.groovy:29)
at java.lang.Thread.run(Thread.java:619)

Hello, Peter,

Amazing article, and great response to all the feedback.

I have an Eclipse project with our existing Hibernate domain models. I created a new Grails Project in Eclipse, and then added my domain project under Preferences/Java Build Path/Projects.

I generated the hibernate.cfg.xml file, and added both and
entries.

Unfortunately, when I try to 'grails run-app', I get a (deeply nested) exception:
nested exception is org.hibernate.MappingException: Unable to load class declared as in the configuration:

Apparently, my grails project hibernate configuration cannot find the class. Any thoughts on what else I could do?

Also, the error was:

Unable to load class declared as <mapping class="com.MyPackage.MyClass"/> in the configuration:
… 23 more

Hi, Peter,

I have tried connecting the project via Eclipse Java Build Path, and I have tried explicitly copying the JAR file into the grails project's lib directory, but always get the "Unable to load class" error. (I am trying to avoid recopying the .java files over from the original project.)

Thanks for the quick response. I am on IRC at freenode#grails channel if you'd like to chat, otherwise I'll take whatever help I can get.

Figured out my problem. I am migrating a struts app to Grails and reusing the JPA entities. The entities were implementing Acegi interfaces, which caused the exception.
But it is really strange that this results in ClassNotFoundException. It is very misleading.

I have some JPA annotated classes from a Jar file that I use to create my domain classes,
everything works fine, connection to the DB is perfect, but the only caviat are the constraints which are ignored, I've red thru this article and added the package.DomainClassConstraints.groovy to src/java as mentioned in this article,

From here everything looks good, but when I run the app the console gets into an infinite cycle…
and keeps re-compiling without end… any pointings about this?

Running Grails application..
Configuring Spring Security …
Server running. Browse to http://localhost:8080/my-app

Running Grails application..
Configuring Spring Security …
Server running. Browse to http://localhost:8080/my-app

Thanks for the earlier response Peter.
I am still struggling with the configuration. I have quite a lot of modular code already written in Spring and JPA and i want to reuse the back end code and migrate only the struts 2 app to grails. I am using maven as the build tool and have added dependencies to other maven modules. I followed the maven plugin documentation for grails and the project seems setup properly. I am trying to run the mvn grails:exec -Dcommand=generate-controller and passing an existing JPA class as the -Dargs.
I end up error that says 'beanName' must not be empty. I am pretty sure i have all the correct dependencies set up, but the command refuses to run successfully.
Any hints on what might be happening? Thanks for your help.

Brief stack trace is as follows

Caused by: java.lang.IllegalArgumentException: 'beanName' must not be empty
at org.springframework.util.Assert.hasText(Assert.java:162)
at org.springframework.beans.factory.config.RuntimeBeanReference.(RuntimeBeanReference.java:58)
at org.springframework.beans.factory.config.RuntimeBeanReference.(RuntimeBeanReference.java:46)
at org.springframework.transaction.config.AnnotationDrivenBeanDefinitionParser.parseInternal(AnnotationDrivenBeanDefinitionParser.java:76)
at org.springframework.beans.factory.xml.AbstractBeanDefinitionParser.parse(AbstractBeanDefinitionParser.java:59)
at org.springframework.beans.factory.xml.NamespaceHandlerSupport.parse(NamespaceHandlerSupport.java:73)

Thanks a lot for the post Peter. I notice you haven't mentioned installing any of the JPA plugins. Is there any benefit to installing one of the JPA plugins if we follow the approach outlined in this post?

@Peter: Thanks for your response, but I'm not sure I understand the difference. If I have my domain model classes annotated with the javax.persistence annotations such as @Entity and I'm using Hibernate as my JPA provider (implmementation), does that mean I'm using JPA directly or Hibernate?

There's a line missing from the previous comment. After:

"…Spring picks them up from the classpath due to the following definition in appContext.xml:"

The following should appear:

<context:component-scan base-package="com.service.impl"/>

Thanks again Peter. Do you know if there are any sample Grails-JPA 2.0 applications that demonstrate how to integrate a JPA 2.0 domain model (and Spring config) into a new Grails app?

Apart from this blog post, the only substantial information I've been able to find is this article: http://bit.ly/qJLYVO
which is 2-years-old and only covers JPA 1.0. BTW, the GORM-JPA plugin docs state:

"Dynamic finders are supported by the plugin, but since JPA 1.0 doesn't support Criteria, criteria queries are not."

Does this mean that this plugin only supports JPA 1.0? If so, then is the GORM Hibernate plugin (the approach detailed in this article), the only option for JPA 2.0?

Maybe I'll step up to the plate and write a JPA 2.0-Grails tutorial using my current project as an exemplar. Thanks again for your feedback, would you mind letting me know if the following is an accurate summary of our discussion?

Hibernate Plugin
—————
- JPA classes configured in hibernate.cfg.xml
- Constraints configured in src/java
- Provides full GORM functionality
- Supports JPA 2.0

GORM-JPA Plugin
—————
- Provides limited GORM functionality, e.g. no countBy, listOrderBy dynamic finders or criteria queries
- Suppprts JPA 1.0 only (not sure about this??)

Spring
======
Existing Spring config can either be imported from classpath into resources.groovy using the BeanBuilder's importBeans method, or copied to grails-app/conf/spring

Packages that should be scanned for annotated beans must be configured in Config.groovy

Grails
======
Support for JPA 2.0 with Hibernate 3.6 is not available in versions of Grails prior to 2.0

@Peter I eventually realised that I need to do my persistence using the JPA EntityManager rather than Hibernate. Based on some of your previous remarks, I should use the GORM-JPA plugin. However, judging by the example persistence.xml shown on that plugin's page, it looks like it only supports JPA 1.0, is that right?

@Peter – thanks I'll see if I can get it working with JPA 2.0 and post the results here. Do you know if you can use GORM constraints (in the manner described above) when using JPA directly, i.e. with the GORM-JPA plugin installed and configured?

How do you unit test constraints in this scenario? I tried "mockForConstraintsTests", but Grails seems not to add the constraints to the domain class such that validation always returns 'true'. Any idea?

@Peter Is there a tool or easy way to convert Hibernate mapped models to GORM models? I would like to take advantage of my existing Hibernate models (without re-writing them to GORM models by hand) but also be able to write unit tests with them.

Hi,

cool article, Im also reusing a java hibernate model in a grails app. I've solved most issues but have problem with grails not figuring out that a column is called 'userId'. The generated sql shows 'user_id'

heres the mapping in the java entity

@OneToOne
@JoinTable(
name = "ql_user2hotel",
joinColumns = {@JoinColumn(name = "hotelId")},
inverseJoinColumns = {@JoinColumn(name = "userId")}
)
private User user;

I dont really want to touch the java entities (as im copying them from one module to another in my during my buiid lifecycle), so my question is this: Is it possible to define a new file to override the mapping via groovy meta magic a bit like you do above for the constraints?

or is there another way around this ?

hope you can help

thanks