Implementing interfaces on Grails Domains

domainsAndInterfaces.groovy

interface Buyable {
    def buy()
}

class UpperClass {}
class ChildClass extends UpperClass {}

class SomeBuyableObject extends UpperClass implements Buyable {
    String foo
    def buy() { //do stuff }
}

class AnotherBuyableObject extends ChildClass implements Buyable {
    String bar
    def buy() { //do stuff }
}



class MyService {
    def abbreviate(String name) {
        return name.collect { Character.isUpperCase(it as Character)?it.toLowerCase():'' }.join()
    }

    def listBuyables() {
        new SomeBuyableObject(foo: 'foo').save()
        new AnotherBuyableObject(bar : 'bar').save()
        
        //doest work
        //  def buyables = Buyable.findAll() // GORM find all
        def classes = grailsApplication.domainClasses.findAll {
            Buyable.isAssignableFrom(it.clazz)
        }.name
	
        def tables = classes.each{ it += abbreviate(it) }.join(', ')
	
        def query = "from "+tables
        def buyables = UpperClass.executeQuery(query)[0]
        assert buyables.size() == 2
    }
}

Vai ficar uma query do tipo:
"from SomeBuyableObject sbo, AnotherBuyableObject abo"