Fetch fields from table or structure in ABAP SAP

If you need to identify the fields and number of fields in a structure, then you should use runtime type services. Using runtime type services makes more sense in this case as if we have some data in our environment, then it's not ideal to call database for fetching the same.

Using Runtime Type Services

Runtime type services provide a way to analyze the structure of data objects at runtime. Here's how to get field information from a structure ?

DATA(structure) = VALUE <your_structure>( ).
DATA(Descriptor) = CAST cl_abap_structdescr( cl_abap_datadescr=>describe_by_data( structure ) ).
DATA(Fields) = LINES( Descriptor->components ).

This will give you the count of the components of the table or structure. The cl_abap_structdescr class provides detailed information about structure components.

Alternative Database Query Method

You can also try another option if you do not want to use runtime type services. The following query can get you the field count from the data dictionary ?

SELECT COUNT(*) INTO @DATA(count)
FROM dd03l
WHERE tabname = '<STRUCTURE_NAME>'
  AND as4local = 'A'.

The DD03L table stores the field information of SAP tables and structures. The condition as4local = 'A' ensures you get only active fields.

Complete Example

DATA: ls_structure TYPE sflight.

" Method 1: Runtime Type Services
DATA(lo_descriptor) = CAST cl_abap_structdescr( 
  cl_abap_datadescr=>describe_by_data( ls_structure ) ).
DATA(lv_field_count) = LINES( lo_descriptor->components ).

WRITE: / 'Number of fields using RTS:', lv_field_count.

" Method 2: Database Query
SELECT COUNT(*) INTO @DATA(lv_db_count)
FROM dd03l
WHERE tabname = 'SFLIGHT'
  AND as4local = 'A'.

WRITE: / 'Number of fields from DD03L:', lv_db_count.

Conclusion

Runtime type services are the preferred method for analyzing structure fields when data is already available in memory, while database queries against DD03L are useful for getting field information directly from the data dictionary.