View source for Virtual fields in CDS Views

[[category: Core_data_services]]
It is often necessary to supply data in a CDS view, as simple connections/relationships through CDS views are not possible and more complex coding is required. The calculation logic, in particular, is used to fill a field with a specific value. For performance reasons, you should use it as sparingly as possible.

In my case, I developed an app with RAP and was able to map it completely using CDS views except for a few columns. 

== Introduction ==

Virtual fields are implemented with ABAP classes and have been available since SAP NetWeaver Release 7.51.

A distinction is made between three categories:
* virtual fields with their own calculation logic
* virtual fields with their own sort logic
* virtual fields with their own filter logic

A few facts:
* Virtual fields are only addressed within the OData framework. Queries of the CDS view via Open SQL Selects return no results, i.e. the underlying class is not run through
* Virtual fields do not know each other
* Filter logic cannot be applied to virtual fields and is explicitly intercepted in the further SADL code
* Key fields cannot be defined as virtual elements

== Declaration in CDS view using the example of calculation logic ==
Virtual fields can be used where they are supported, e.g. in EXTEND VIEW ENTITY:
<syntaxhighlight lang="abap" line start="1">
define view <CdsConsumptionView>
		as select from <data_source>
{
		...
		@ObjectModel.readOnly: true
		@ObjectModel.virtualElement
		@ObjectModel.virtualElementCalculatedBy: 'ABAP:<code_exit_class>'
		cast( '' as <dtype> preserving type) as <view.element>
		...
}
</syntaxhighlight>

The notation is slightly different in projection views:
<syntaxhighlight lang="abap" line start="1">
define root view entity <CdsProjectionView>
  provider contract transactional_query
  as projection on <data_source>
{
       ...
       @ObjectModel. virtualElementCalculatedBy: 'ABAP:<code_exit_class>'
       virtual <view.element> : abap.<type>
       ...
}
</syntaxhighlight>

Similarly for filtering and sorting, see useful pages.

== Exit classes ==
For the three possible cases of virtual elements, a class must be created that is marked with a marker, i.e. INTERFACE, so that the method header is used as specified in the INTERFACE. How the method body is programmed can be seen as follows for all logics.

=== Calculation logic ===
For a bonus and analysis app, it was necessary to calculate the current turnover. This could not simply be determined using CDS views and had to be calculated.

I got into the habit of designating the exit class as a suffix with _CALC.

<syntaxhighlight lang="abap" line start="1">
CDS-View
		...
		@ObjectModel. virtualElementCalculatedBy: 'ABAP:YCL_CCM_AMOUNT_CALC'
		virtual amount              : abap.dec( 13,2 ), //abap.dec( 15,2 ), //wcb_scale
		...
</syntaxhighlight>

<syntaxhighlight lang="abap" line start="1">
CLASS ycl_ccm_amount_calc DEFINITION
  PUBLIC
  FINAL
  CREATE PUBLIC .

  PUBLIC SECTION.
    INTERFACES if_sadl_exit_calc_element_read.
  PROTECTED SECTION.
  PRIVATE SECTION.
ENDCLASS.

CLASS ycl_ccm_amount_calc IMPLEMENTATION.

  METHOD if_sadl_exit_calc_element_read~calculate.

    DATA orig_data TYPE STANDARD TABLE OF <cds_view_with_exit_class>.
    FIELD-SYMBOLS <orig_data> TYPE <cds_view_with_exit_class>.

    MOVE-CORRESPONDING it_original_data TO orig_data.

    LOOP AT orig_data ASSIGNING <orig_data>.

      try.
       <orig_data>-amount = <method_of_a_class_to_calc_amount>
     catch cx_root into DATA(cx).
       <orig_data>-amount = 0.
      endtry.

    ENDLOOP.
    MOVE-CORRESPONDING orig_data TO ct_calculated_data.

  ENDMETHOD.
</syntaxhighlight>

It is possible to use the get_calculation_info method to add only the required elements or to check whether the correct CDS view triggers this class.

<syntaxhighlight lang="abap" line start="1">
 METHOD if_sadl_exit_calc_element_read~get_calculation_info.

  IF iv_entity <> '<your_cds_view'.
   RAISE EXCEPTION TYPE ...
  ENDIF.
 
  IF line_exists( it_requested_calc_elements[table_line = 'XYZ' ] ) .
   INSERT: conv sadl_entity_element( 'field' ) INTO TABLE et_requested_orig_elements.
  ENDIF.

 ENDMETHOD.
</syntaxhighlight>

=== Sort logic ===

<syntaxhighlight lang="abap" line start="1">
CLASS <classname> DEFINITION
  PUBLIC
  FINAL
  CREATE PUBLIC .
 
  PUBLIC SECTION.
    INTERFACES if_sadl_exit_sort_transform.
 
  PROTECTED SECTION.
 
  PRIVATE SECTION.
 
ENDCLASS.

CLASS <classname> IMPLEMENTATION.
 
  METHOD if_sadl_exit_sort_transform~map_element.
 
    IF iv_entity <> '<cds_view_name>'.
      RAISE EXCEPTION TYPE ...
    ENDIF.
 
    IF iv_element = 'AMOUNT'.
      et_sort_elements = VALUE #(
        ( name = 'AMOUNT' ) ( name = 'CONDITIONCONTRACT' )
      ).
    ENDIF.
 
  ENDMETHOD.
 
ENDCLASS.
</syntaxhighlight>

=== Filter logic ===

<syntaxhighlight lang="abap" line start="1">
CLASS <classname> DEFINITION
  PUBLIC
  FINAL
  CREATE PUBLIC .
 
  PUBLIC SECTION.
    INTERFACES if_sadl_exit_filter_transform.
 
  PROTECTED SECTION.
 
  PRIVATE SECTION.
 
ENDCLASS.

CLASS <classname> IMPLEMENTATION.
 METHOD if_sadl_exit_filter_transform~map_atom.
  DATA: condition_manager TYPE REF TO if_sadl_simple_cond_factory,
        filter            TYPE REF TO if_sadl_simple_cond_element,

  IF iv_element <> '<cds_view_name>'.
      RAISE EXCEPTION TYPE ...
  ENDIF.

 condition_manager = cl_sadl_cond_prov_factory_pub=>create_simple_cond_factory( ).
 filter->element('FIELD' ).

 CASE iv_operator.
  WHEN if_sadl_exit_filter_transform~co_operator-equals( ... ).
   ...
  WHEN if_sadl_exit_filter_transform~co_operator-less_than( ... ).
   ...
  WHEN if_sadl_exit_filter_transform~co_operator-greater_than( ... ).
   ro_condition = filter->greater_than( <parameter> ).
  WHEN OTHERS.
   RAISE EXCEPTION TYPE cx_sadl_exit_filter_not_supp.
  ENDCASE.
 ENDMETHOD.
ENDCLASS.
</syntaxhighlight>

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