Updating custom field in table EKKO within user exit when PO is saved

Question

I am trying to update a custom field in table EKKO when a PO is saved.  I am using FM EXIT_SAPMM06E_013, within enhancement MM06E005.  Since EKKO is not a table that can be updated with this user exit, I am using a technic that I read about on SDN where I assign a field symbol to the calling program variable and then am able to access data within EKKO table.  But when I pass this data back into the field symbol, for some reason this field is not getting saved when the PO is saved.  In debug mode, it looks like this field is getting updated, but when I look in the table after the PO is saved, it is not there.  My code sample is below.  What I am doing wrong?
data:
  CHAR(50) VALUE '(SAPLMEPO)EKKO-ZHDRCSTCENTER',
  g_zhdrcstcenter like ekko-zhdrcstcenter,
  FIELD-SYMBOLS <F1> type any.
if i_ekko-ekorg = '5401'.
  ASSIGN (char) to <F1>.
  g_zhdrcstcenter = <F1>.
  move '0000113322' to g_zhdrcstcenter.
  <F1> = g_zhdrcstcenter.
endif.
Thanks!
Sarah Smyth.

Answer 1

Firstly, have you investigated using EXIT_SAPMM06E_008 to set any custom fields you have added in the EKKO_CI / CI_EKKODB structure?.. that might work more easily.
In terms of doing an assign back into a calling program's memory, it can work but it's probably worth setting a break point in your code then stepping through watching the values in EKKO - sometimes you can find subsequent code that re-writes an earlier copy of values back into the structure, thereby preventing you doing your change...  SAP does warn this method is for "internal use".  Also check in your debugger that it's SAPLMEPO and not SAPMM06E you need.