Grails controllers are not very DRY. It’s easy to find duplicated code fragments in default generated controller. Take a look at code sample below. It is duplicated four times in show, edit, update and delete actions:
class BookController {
def show() {
def bookInstance = Book.get(params.id)
if (!bookInstance) {
flash.message = message(code: 'default.not.found.message', args: [message(code: 'book.label', default: 'Book'), params.id])
redirect(action: "list")
return
}
[bookInstance: bookInstance]
}
}
Why is it duplicated?
There is a reason for that duplication, though. If you move this snippet to a method, it can redirect to "list" action, but it can’t prevent controller from further execution. After you call redirect, response status changes to 302, but after method exits, controller still runs subsequent code.
Solution
At TouK we’ve implemented a simple trick to resolve that situation:
- wrap everything with a simple
withStoppingOnRendermethod, - whenever you want to render or redirect AND stop controller execution – throw
EndRenderingException.
We call it Big Return – return from a method and return from a controller at once. Here is how it works:
class BookController {
def show(Long id) {
withStoppingOnRender {
Book bookInstance = Book.get(id)
validateInstanceExists(bookInstance)[bookInstance: bookInstance]
}
}
private void validateInstanceExists(Book instance) {
if (!instance) {
flash.message = message(code: 'default.not.found.message', args: [message(code: 'book.label',
default: 'Book'), params.id])
redirect(action: "list")
throw new EndRenderingException()
}
}
}
class EndRenderingException extends RuntimeException {}
Example usage
For simple CRUD controllers, you can use this solution and create some BaseController class for your controllers. We use withStoppingOnRender in every controller so code doesn’t look like a spaghetti, we follow DRY principle and code is self-documented. Win-win-win! Here is a more complex example:
class DealerController {
@Transactional
def update() {
withStoppingOnRender {
Dealer dealerInstance = Dealer.get(params.id)
validateInstanceExists(dealerInstance)
validateAccountInExternalService(dealerInstance)
checkIfInstanceWasConcurrentlyModified(dealerInstance, params.version)
dealerInstance.properties = params
saveUpdatedInstance(dealerInstance)
redirectToAfterUpdate(dealerInstance)
}
}
}
