Some time ago ABAP surprised me with a nice feature. I saw an interesting SELECT statement during a code review. Here is the SELECT statement. For demonstration purpose I changed the statement a little bit.
SELECT SINGLE 'X'
FROM seoclass
WHERE clsname = 'CL_GUI_FRONTEND_SERVICES'
INTO @data(x).
CHECK sy-subrc = 0.
Right away I noticed the "X" behind the term "SINGLE". I hadn't seen such a combination before. Or I couldn't remember it. In any case, I didn't use this syntax yet.
Out of interest, I asked a colleague. He had the right answer: You can check if there is a row in the database table that meets the WHERE condition. With this hint I remembered that I had read about it someday. There was a
blog by Horst Keller (and also the
link to the SAP online help). From 7.40 SP05 this feature exists. Here is the example from the SAP Online Help.
SELECT SINGLE @abap_true
FROM scarr
WHERE carrid = @carrier
INTO @DATA(exists).
IF exists = abap_true.
cl_demo_output=>display( |Carrier { carrier } exists in SCARR| ).
ELSE.
cl_demo_output=>display( |Carrier { carrier } does not exist in SCARR| ).
ENDIF.
By using the variable "exists" it's much more clear what the statement meant. Because of the challenge to write "easy to understand" source code, I then tried the following example.
CONSTANTS entry_exists TYPE abap_bool VALUE abap_true.
SELECT SINGLE @entry_exists
FROM seoclass
WHERE clsname = 'CL_GUI_FRONTEND_SERVICES'
INTO @DATA(answer_from_db).
IF answer_from_db = entry_exists.
WRITE 'Entry exists.' COLOR COL_POSITIVE.
ELSE.
WRITE 'Entry does not exist.' COLOR COL_NEGATIVE.
ENDIF.
This is valid and works. And a little bit more understandable. However, an additional comment could be useful. According to
"Clean ABAP" styleguide, there is another solution so we can omit the comment: Put the source code in a separate method with a suitable name, something like "IS_CLASS_AVAILABLE" in my demo. This could look like this (I omitted some source code parts).
[..]
CLASS-METHODS is_class_available
IMPORTING
class_name TYPE seoclsname
RETURNING
VALUE(result) TYPE abap_bool.
[..]
METHOD is_class_available.
CONSTANTS entry_exists TYPE abap_bool VALUE abap_true.
SELECT SINGLE @entry_exists
FROM seoclass
WHERE clsname = @class_name
INTO @result.
IF sy-subrc <> 0.
ENDIF.
ENDMETHOD.
[..]
IF lcl_test=>is_class_available( 'CL_GUI_FRONTEND_SERVICES' ) = abap_true.
WRITE 'Class exists.' COLOR COL_POSITIVE.
ELSE.
WRITE 'Class does not exist.' COLOR COL_NEGATIVE.
ENDIF.
Ok, with this solution I was happy. For now
😉 Perhaps how to handle sy-subrc is worth a discussion.
As a hint: If you are interested in performance discussions about checking if a row exists, you should read the comments on Horst Keller's
blog.
Best regards and thanks for reading
Michael
