Validating a selection screen filed

Question

Hi Experts,
I need to to validate a selection screen field .The field is mentioned as selection parameter and it is obligatory.
To validate this i have written the logic as follows:
AT SELECTON SCREEN ON <FIELD-NAME>.
SELECT STATEMENT.
IF SY-SUBRC NE 0.
ERROR MESSAGE.
endif.
But here my question is select-options acts like an intenal table,Inthis case do we need to loop to the select-options fields or else do we have any other alternative solution.
Edited by: vinay raj on Aug 31, 2010 10:51 AM

Answer 1

Hi,
Looping is not required for this validation.  And as you have said select statement using IN oerator does not throw any error message if the value is not present in select-options.
AT SELECTON SCREEN ON <FIELD-NAME>.
SELECT STATEMENT .... where field in s_field.
IF SY-SUBRC NE 0.
ERROR MESSAGE.
endif.
But if you want to check whether the value entered in select-options is invalid then you can refer the below sample code
which can be used to check for the validity of the value  of valuation class entered in the selection screen where valuation class is used as select-options. In the below code table T025 has all the values of valuation class. If the entered value does not exist in this then it indicates that the value entered in selection screen is invalid. 
AT SELECTON SCREEN ON <FIELD-NAME>.
PERFORM check_valuation_class.
FORM check_valuation_class.
  DATA : lv_bklas TYPE bklas.
  IF NOT p_bklas-low IS INITIAL.
    SELECT SINGLE COUNT(*) FROM t025
    INTO (lv_bklas) WHERE bklas EQ p_bklas-low.
    IF sy-subrc NE 0.
      MESSAGE e021(zfm001).
    ENDIF.
  ENDIF.
  IF NOT p_bklas-high IS INITIAL.
    SELECT SINGLE COUNT(*) FROM t025
    INTO (lv_bklas) WHERE bklas EQ p_bklas-high.
    IF sy-subrc NE 0.
      MESSAGE e021(zfm001).
    ENDIF.
  ENDIF.
ENDFORM.                    " check_valuation_class