Question

preface note: I’m just starting to learn Grails, so I’m sure there are many other problems and room for optimization.

I’ve got two domains, a parent (Collection) and child (Event), in a one-to-many mapping. I’m trying to code an integration test for the deletion of children. Prior to the code in question, I’ve successfully created a parent and three children. The point where I’m having problems is getting a single child in preparation to delete it. The first line of my sample code is only there because of my rudimentary attempt to troubleshoot.

// lines 95-100 of my EventIntegrationTests.groovy file
// delete a single event
assertEquals("2nd Event", event2.title)     // passes
def foundEvent = Event.get(event2.id)       // no apparent problems
assertEquals("2nd Event", foundEvent.title) // FAILS (line #98)
foundEvent.delete()
assertFalse Event.exists(foundEvent.id)

The error message I’m getting is:

 Cannot get property 'title' on null object 

 java.lang.NullPointerException: Cannot get property 'title' on null object
         at edu.learninggrails.EventIntegrationTests.testEventsDelete(EventIntegrationTests.groovy:98)

What should my next troubleshooting steps be? (Since the first assertEquals passes, event2 is clearly not null, so at this point I have no idea how to troubleshoot the failure of the second assertEquals.)

Answer 1

This is not evident from the code: did you persist event2 by calling save()? Get will try to retrieve it from the persistent storage (the in-memory database for example) and if the event wasn’t saved, the retrieved instance will be null.

If you did save it, did the save go through OK? Calling event.save() will return false if there was something wrong while saving the item (like a validation error). Lastly, you might try calling event.save(flush:true) in case the Hibernate session doesn’t handle this case as you might expect (I’m not entirely sure about this one, but it can’t hurt to try).