Grails : How to persist Master Detail Relationship - grails

Question

I have built a UI that allows you to enter a Master Record ( VocabularyTest ) and a set of Detail Records ( VocabQuestion ) on the same form. I'm pretty happy that the data that is being submitted is correct, but when I try to save the Master record, I get the following error
null id in vocabularytest.VocabQuestion entry
EDIT - The Complete stacktrace is
null id in vocabularytest.VocabQuestion entry (don't flush the Session after an exception occurs). Stacktrace follows:
Message: null id in vocabularytest.VocabQuestion entry (don't flush the Session after an exception occurs)
Line | Method
->> 24 | save in vocabularytest.VocabularyController
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
| 195 | doFilter in grails.plugin.cache.web.filter.PageFragmentCachingFilter
| 63 | doFilter in grails.plugin.cache.web.filter.AbstractFilter
| 1110 | runWorker in java.util.concurrent.ThreadPoolExecutor
| 603 | run . . . in java.util.concurrent.ThreadPoolExecutor$Worker
^ 722 | run in java.lang.Thread
END EDIT
I'm assuming that this is happening as the Foreign Key reference on my Detail record is null, which wouldn't surprise me unduly, as I'm doing nothing to set it.
The Params that are being received by my controller are as follows
title: Dave New Test
testItems[0].question: Q1
testItems[0].answer: A1
testItems[1].question: Q2
testItems[1].answer: A2
testItems[2].question: Q3
testItems[2].answer: A3
create: Create
My domain Objects are
class VocabularyTest {
static hasMany = [testItems: VocabQuestion]
static constraints = {
}
String title;
List <VocabQuestion>testItems = LazyList.decorate(
new ArrayList(),
FactoryUtils.instantiateFactory(VocabQuestion.class));
}
class VocabQuestion {
static constraints = {
}
String question
String answer
VocabularyTest vocabularyTest
}
The relevant method of my controller is
def save() {
log.debug(params)
def vocabularyTestInstance = new VocabularyTest(params)
if (!vocabularyTestInstance.save(flush: true)) {
render(view: "create", model: [vocabularyTestInstance: vocabularyTestInstance])
return
}
flash.message = message(code: 'default.created.message', args: [message(code: 'vocabularyTest.label', default: 'VocabularyTest'), vocabularyTestInstance.id])
redirect(action: "index", id: vocabularyTestInstance.id)
}
Am I trying to do something that GORM and Grails will allways struggle to do, or am I just missing something vital?

Answer 1

Try this:
class VocabularyTest {
static hasMany = [testItems: VocabQuestion]
static constraints = {
}
String title
List testItems
}
class VocabQuestion {
static constraints = {
}
static belongsTo = [vocabularyTest: VocabularyTest]
String question
String answer
}