Summary on Transaction Rollback in Grails

This post is a summary on how to rollback transactions in grails application, and highlights a stain in grails reference document.

Rollback Programmatic Transactions

In Grails, we can use withTransaction method on domain classes to deal with programmatic transactions. This method takes a closure, which receives a TransactionStatus instance as its first argument. In order to rollback transactions, we can invoke the setRollbackOnly() method on TransactionStatus. Here is an example from grails reference document:

Account.withTransaction { status ->
 def source = Account.get(params.from)
 def dest = Account.get(params.to)
 def amount = params.amount.toInteger()

 if(source.active) {
     source.balance -= amount
     if(dest.active) {
         dest.amount += amount
     }else {
         status.setRollbackOnly()
     }
 }
}

Rollback Declarative Transactions

With service, it's not a big deal to implement declarative transactions in grails. If you want to rollback, all that you need to do is to throw a RuntimeException or its subclass in service method. The following code shows how to do this job:

class DomainbService {
 boolean transactional = true

 def service2() {
     new B().save()
     throw new RuntimeException("save b failed!")
 }
}

There is one thing you should notice: grails refernce document doesn't spot the exception you throw in method must be an RuntimeException object. Actually, if you throw an Exception object, the transaction doesn't rollback. You can have a test to verify this. And in spring reference document, you can find that you should throw an "unchecked" exception to trigger a rollback when you are using declarative transaction.