How to traverse back in Mapping?

Question

If the source delivers the data always in the same order, there's an easier way to achieve this.Within an Expression transformation, you can define variable ports which automatically are initialised to certain values. For example, a numeric variable port will always be initialised to 0 (zero), and strings will always be initialised to an empty string.Now with a small trick one can store the value of the trade ID from the first record and then simply use it from that time onward. This trick uses the fact that variable ports are always processed from top to bottom.Set up one variable port named "v_is_read" of type Integer with this expression:  TRUENow set up another variable port "v_trade_id" of the same data type as the TRADE_ID port immediately before v_is_read with this expression:  IIF( v_is_read, v_trade_id, TRADE_ID)Finally forward the value of v_trade_id as an output port ORIGINAL_ID. How does that work?When the very first record is processed, all variable ports are initialised, meaning "v_is_read" is set to 0 and "v_trade_id" is set to an empty string.Now all input ports are read from top to bottom.Next come all the variable ports. Because "v_trade_id" comes before "v_is_read", the variable port "v_is_read" still has its initialisation value of 0, so the IIF() function above will be evaluated by setting v_trade_id to the current value of the TRADE_ID port (which is the value of the very first input record).After that "v_is_read" will be set to TRUE (and will keep this value throughout the whole session run).Now for all following records the IIF() invokation will simply keep the value that's currently stored in "v_trade_id", and that is the value of the port TRADE_ID from the very first input record. This trick works perfectly with flat file sources and with relational sources which are sorted. Regards,Nico

Answer 1

Hi, I have a scenario like below: Source: Has three columns as below: Trade_ID,Trade_value,Route_ID101,10,NULL102,10,101103,10,102104,10,103105,10,104...So On. My Target Has 4 columns as below: The Original ID should be the Trade ID of very first record of source. Trade_ID,Trade_value, Route_ID, Original_ID101,10,NULL,101102,10,101,101103,10,102,101104,10,103,101105,10,104,101...So On. How to implement above scenario using mapping. Is it possible to traverse back until the first record in mapping.