GORM Composite mapping not working - grails

Question

On grails 2.4.3 and postgresql as the database I have:
class ClassA {
Set classB = []
static belongsTo = [classC: ClassC]
static hasMany = [classB: ClassB]
}
and:
#EqualsAndHashCode
class ClassB implements Serializable {
ClassA classA
Integer number
static belongsTo = [classA: ClassA]
static mapping = {
id composite: ['number', 'classA']
}
And I'm getting this weird error:
[localhost-startStop-1] ERROR context.GrailsContextLoaderListener - Error initializin
the application: Error creating bean with name 'transactionManagerPostProcessor':
Initialization of bean failed; nested exception is
org.springframework.beans.factory.BeanCreationException: Error creating bean with name
'transactionManager': Cannot resolve reference to bean 'sessionFactory' while setting
bean property 'sessionFactory'; nested exception is
org.springframework.beans.factory.BeanCreationException: Error creating bean with name
'sessionFactory': Invocation of init method failed; nested exception is
java.lang.NullPointerException Message: Error creating bean with name
'transactionManagerPostProcessor': Initialization of bean failed; nested exception is
org.springframework.beans.factory.BeanCreationException: Error creating bean with name
'transactionManager': Cannot resolve reference to bean 'sessionFactory' while setting
bean property 'sessionFactory'; nested exception is
org.springframework.beans.factory.BeanCreationException: Error creating bean with name
'sessionFactory': Invocation of init method failed; nested exception is
java.lang.NullPointerException Line | Method ->> 266 | run in
java.util.concurrent.FutureTask - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - | 1142 | runWorker in java.util.concurrent.ThreadPoolExecutor | 617 |
run . . . in java.util.concurrent.ThreadPoolExecutor$Worker ^ 745 | run in
java.lang.Thread
What is going on? What I am doing wrong?

Answer 1

not sure, what the message means, but this is wrong:
Set ClassB = []
it should be
Set<ClassB> classB = new HashSet<>()
UPDATE:
see the refdoc. the fields should be of primitive types I'd say.
try converting extracting a property out of the ClassB instance:
#EqualsAndHashCode
class ClassB implements Serializable {
ClassA classA
String someAProp
Integer number
void setClassA( ClassA a ){
classA = a
someAProp = a.someProp
}
static belongsTo = [classA: ClassA]
static mapping = {
id composite: ['number', 'someAProp']
}
}