Create table type by name then add an arbitrary column?

I am attempting to write a class that can accept a table name, add a couple of extra columns for data ingestion purposes, then generate a CSV. I have it working for a table by sending in a table name as a parameter:

" Get the data dictionary object for the table
table_type ?= cl_abap_typedescr=>describe_by_name( table ).
" Create a table description object with the line type
table_descr = cl_abap_tabledescr=>create( p_line_type = table_type ).
" Declare the internal table using the generic type
create data gt_data type handle table_descr.

This generic code gets me home to then create a SQL call via cl_sql_statement and fill the gt_data object. My question is:

Can I add a column to the generic type? I wanted to add a timestamp column to the front of the object as to when I have extracted the data from the system.

I also may want to run queries with a JOIN where I may need a single field from another table that the generic type doesn't handle, so I may need to add a single extra column. How can this be done?

Solution

Youre pretty close to the solution already. Using the RTTS classes.
There is an example in your ABAP system that does what you are looking for.

See ABAP demo_create_data_via_handle The Docu covers this process as well.

Here is a snippet from the Program.

METHOD main.
    DATA: struct_type TYPE REF TO cl_abap_structdescr,
          dref        TYPE REF TO data,
          oref        TYPE REF TO cx_sy_struct_creation.

    DATA column1 TYPE c LENGTH 30.
    DATA column2 TYPE c LENGTH 30.

    FIELD-SYMBOLS: <struc>  TYPE any,
                   <comp1>  TYPE any,
                   <comp2>  TYPE any.

    cl_demo_input=>add_field( CHANGING field = column1 ).
    cl_demo_input=>add_field( CHANGING field = column2 ).
    cl_demo_input=>request( ).

    column1 = to_upper( column1 ).
    column2 = to_upper( column2 ).

    TRY.
        struct_type = cl_abap_structdescr=>get(
          VALUE #(
            ( name = column1 type = cl_abap_elemdescr=>get_c( 40 ) )
            ( name = column2 type = cl_abap_elemdescr=>get_i( )    )
                 )
                                               ).
        CREATE DATA dref TYPE HANDLE struct_type.
      CATCH cx_sy_struct_creation INTO oref.
        cl_demo_output=>display( oref->get_text( ) ).
        RETURN.
    ENDTRY.

    ASSIGN dref->* TO <struc>.
    ASSIGN COMPONENT column1 OF STRUCTURE <struc> TO <comp1>.
    <comp1> = 'Amount'.

    ASSIGN dref->* TO <struc>.
    ASSIGN COMPONENT column2 OF STRUCTURE <struc> TO <comp2>.
    <comp2> = 11.

    cl_demo_output=>display( |{ column1 WIDTH = 32 } { <comp1> }\n| &
                             |{ column2 WIDTH = 32 } { <comp2> }| ).
  ENDMETHOD.