====== Service ======
Grails service mainly handle the business logic passed from the controller, and database access. By adding a ''@Transcational'' annotation, it will be wrap all methods within that service in a transaction. In case of any exception, it will roll-back automatically so that the database will not be modified.  The controller class must located at /grails-app/services/ directory. 

===== Creating a Service=====
There are two ways to do so, and they are listed as follow: 
==== In Grails Console ====
Assume we want to create a service called CatService. we do the following in the console:
<code>
grails create-service cat
</code>
You will find the new files in 
<code>
Created grails-app/services/YOUR_PROJECT/CatService.groovy
Created src/test/groovy/YOUR_PROJECT/CatServiceSpec.groovy
</code>
CatService.groovy is the real deal, and CatServiceSpec.groovy if for unit test. Here is the code generated for the service:
<code>
import grails.transaction.Transactional

@Transactional
class CatService {

    def serviceMethod() {

    }
}
</code>
You can remove the def serviceMethod(){...} and add your own.
==== In Intellij IDEA Ultimate ====
In the Project tree, right click on the \grails-app\services directory, and than select New->Grails Service, and than type the name of service your want.

===== Work with Domain Object =====
Assume we have a Cat domain. We can do the following to obtains all cat objects.
<code>
    @Transactional(readOnly = true)
    List<Cat> getAllCats{
        return Cat.findAll([sort:"name", order:"asc"])
    }
</code>