Is it possible to download multiple files using 'downloadFile'

I am trying to download more than one file and create a zip file.

Inside 'public void downloadfile(DSRequest request, RPCManager rpc)'
when ' request.execute();' statement executes getting error
' ERROR [SQLDataSource] [builtinApplication.myDS_downloadFile] Found more than one record when looking up a binary value on DataSource 'myDS' with criteria . Does the DataSource have a primaryKey declared?'

It works fine, when it returns only one file.

Is it because I am trying to download more than one file?
How can I download more than one file?

Thanks.