How to modify filters in GATEWAY DPC EXT class before GET ENTITY_SET

In some cases we need to modify the filter options in DPC EXT class before it execute GET ENTITY_SET method,

so how to modify the filter options and make them work? follow the following steps:

( you could find sample code in class method /US4G/CL_METERREAD_DAT_DPC_EXT => XUS4GXC_METERR02_GET_ENTITYSET and /US4G/CL_METERREAD_DAT_DPC_EXT => XUS4GXC_MALO_MEL_GET_ENTITYSET )

1)   cast the object io_tech_request_context to type of /iwbep/cl_mgw_request:

DATA(lo_tech_request_context) = CAST /iwbep/cl_mgw_request( io_tech_request_context ).

2)  get the structure of request details by calling  lo_tech_request_context->get_request_details( ) into a local structure ls_request_details:

DATA(ls_request_details) = lo_tech_request_context->get_request_details( ).

3)   writhe your own logic to construct filter options, and fill them into structure ls_request_details–technical_request–filter_select_options,

important: clear the structure ls_request_details–technical_request–filter_expressions ls_request_details–technical_request–filter_functions if your are query root entity;

clear the structure ls_request_details–technical_request–navigation_path if your are query a navigation entity set to avoid query root entity again.

them must be cleared otherwise the modified filters won’t work.

*** modify the structure ls_request_details-technical_request-filter_select_options *** 
CLEAR cs_request_details-technical_request-navigation_path. 
CLEAR: cs_request_details-technical_request-filter_expressions, cs_request_details-technical_request-filter_functions.

4)  create an new lo_model object by calling method /iwbep/cl_mgw_med_provider=>get_med_provider( )->get_service_metadata, passing the service name and version:

DATA(lo_med_provider) = /iwbep/cl_mgw_med_provider=>get_med_provider( ). 
DATA(lo_model) = lo_med_provider->get_service_metadata( 
  EXPORTING iv_internal_service_name = '****SRV' 
            iv_internal_service_version = '0001' ).

5)  create an new lo_new_tech_request_context by using constructor of class /iwbep/cl_mgw_request, and passing the ls_request_details and lo_model:

ro_tech_request = NEW /iwbep/cl_mgw_request( 
  ir_request_details = REF #( is_request_details ) 
  it_headers = VALUE #( ) 
  io_model = CAST #( lo_model ) ).

6) finally pass the new object lo_new_tech_request_context to super class’s GET ENTITY_SET method:

TRY.
        CALL METHOD super->xus4gxc_malo_mel_get_entityset
          EXPORTING
            iv_entity_name           = iv_entity_name
            iv_entity_set_name       = iv_entity_set_name
            iv_source_name           = iv_source_name
            it_filter_select_options = it_filter_select_options
            is_paging                = is_paging
            it_key_tab               = it_key_tab
            it_navigation_path       = it_navigation_path
            it_order                 = it_order
            iv_filter_string         = iv_filter_string
            iv_search_string         = iv_search_string
            io_tech_request_context  = lo_new_tech_request_context
          IMPORTING
            et_entityset             = et_entityset
            es_response_context      = es_response_context.
      CATCH /iwbep/cx_mgw_busi_exception.
      CATCH /iwbep/cx_mgw_tech_exception.
    ENDTRY.