How to get Liferay Dynamic Data Lists RecordId (ddlRecordId) in workflow script

How to get Liferay Dynamic Data Lists RecordId (ddlRecordId) in workflow
script

I'm trying to integrate Liferay Dynamic Data Lists into Kaleo Workflow
(Liferay 6.1 CE GA2), but how to get the ddlRecordId in workflow? I did
some homework, I checked all Attributes in serviceContext, but there is no
"ddlRecordId" in the serviceContext Attribute, only a key named "recordId"
and its value always is 0. Also I can get some field value in the
serviceContext Attributes, such as select and textarea. But what I want is
the upload file field. Thanks.
long ddlRecordId =
GetterUtil.getLong(serviceContext.getAttribute("ddlRecordId"));
DDLRecord ddlRecord = DDLRecordLocalServiceUtil.getRecord(ddlRecordId);