class Validators {
	
    static final confirmPasswordValidator = { value, command ->
        if (command.password != command.confirmPassword) {
            return 'command.confirmPassword.error.mismatch'
        }
    }

    static def requiresAtleastOne =  {val, obj->
        if(!val?.size()){
            return "default.requires.atleast.one"
        }
    }
}


class MyDomain {
	...
	static constraints = {
	      items(validator: requiresAtleastOne)
	}
}