Grails GORM has solid support for using multiple datasources in both 1.3.x with the Datasources plugin, and 2.x with built-in multi-datasource support. This feature allows you to partition your Domain classes and Services to attach to two or more databases. One pitfall you’ll encounter though, is that Integration Tests of the secondary datasources DO NOT rollback their transactions on versions of Grails < 2.3 (GRAILS-9771). However, we can borrow the approach from the 2.3 patch to fix our pre 2.3 test classes!
The approach is simply to add rollback steps for the autowired transactionManager in the JUnit test setUp() and tearDown() methods (or Spock setup() and cleanup()). In this example I have a datasource named “db2” so the injected name of the bean is transactionManager_db2. The test then gets a reference to the transactionStatus in setUp() and rolls it back in tearDown(). (Note: this code was written for a Grails 1.3 app but should also work in 2.x)
Of course the downfall of this approach is that you must remember to setup each test class for a non-default datasource (or use a base test class hierarchy). But this code is essential for integration testing your secondary databases until the app has been migrated to Grails 2.3!
As a reference, here is the configuration I was using for the Datasources plugin in Grails 1.3: