Transfer BOM (bill of material) data from SAP to external database via SAP BC

I deal with problem on SAP BC 4.7 how to transfer BOM lines from SAP to the table located on external system. All the steps which it is required to transfer IDOC structure (BOMMAT03) to SAP BC works well – I get the IDOC values into pipeline. From that point further, I need to transfer just a few variables of one/more* BOM line/record of the IDOC. *(the number of lines depend on chosen transferred BOM item) Therefore I created mentioned procedure on next way: after “transformFlatToHierarchy” service I add MAP step where I mapped particular variables (strings) from IDOC structure with related (Pipeline Out) variables (strings) of newly created record list. The names of that the newly created variables (strings) are the same as names of columns in “destination” table. (When I run SAP BC in trace mode I get values of one record into pipeline.) With the series of MAP steps using transformer “pub.string:concat” and all variables of the record list it is created »SQL string«. Than I mapped the »SQL string« to “$dbSQL” inside “execSQL” service. Such “construction” does not cause any error or message but doesn’t work. According to the trace procedure it stops after first MAP step – the values are assigned to record variables in pipeline. If I run standalone “execSQL” service and insert record variables manually the transfer of data to table of the external database is executed well.
Can anyone help me and write the “working” sequence of services with which it could be transferred data from “transformFlatToHierrachy” step to destination table/database.

Thanks in advance.