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Chapter 4: VAT Report Orchestration

In our journey so far, we've explored the individual components of our VAT report. We learned how users specify what they want in Chapter 1: User Selection Criteria. We saw the finished product in Chapter 2: ALV Grid Presentation, and we defined the data's structure in Chapter 3: Report Data Model.

But how do all these pieces work together? If our program were an orchestra, we've met the individual musicians, but we haven't met the conductor. This chapter is about the conductor—the VAT Report Orchestration—which is the main driver of the program that ensures every part plays its tune at the right time.

The Conductor: START-OF-SELECTION​

Imagine a symphony orchestra. The conductor doesn't play the violin or the trumpet. Instead, they raise their baton, and with a series of gestures, they signal the strings to begin, then the woodwinds to join, and finally the brass section to swell for the grand finale. The conductor orchestrates the performance.

In an ABAP report, the main conductor is an event block called START-OF-SELECTION. This is the part of the code that runs right after the user fills out the selection screen and clicks the "Execute" button. It contains the master plan, the sequence of commands that will take the user's request and turn it into a complete report.

Our program's master plan is beautifully simple. It delegates every major task to a specialized helper subroutine.

* This is the main "conductor" block of our program.
START-OF-SELECTION.

  " Step 1: Get and process the data.
  PERFORM get_amdp_data.

  " Step 2: Prepare the report's column layout.
  PERFORM get_fcat.

  " Step 3: Display the final grid to the user.
  PERFORM disp_data.

This code is the heart of the orchestration. It's easy to read and tells a clear story:

  1. First, call the helper named get_amdp_data to fetch and prepare all the information.
  2. Next, call the helper get_fcat to build the blueprint for our display grid.
  3. Finally, call the helper disp_data to show the finished grid on the screen.

The main program doesn't get bogged down in details. It acts like a good project manager, delegating tasks to the experts and ensuring they are done in the correct order.

Under the Hood: The Sequence of Events​

Let's visualize the flow of control from the user's click to the final report, with our main program acting as the orchestrator.

This diagram shows how the START-OF-SELECTION block acts as a central hub, calling out to different specialized parts of the program to get the job done.

A Closer Look at the Main Helper: get_amdp_data​

The most complex task, fetching and processing the data, is delegated to a single helper: the get_amdp_data subroutine. This helper is a powerhouse that performs several crucial steps:

  1. Packages the Request: It takes the user's input from the selection screen and packages it into a format the database can understand, as we saw in the User Selection Criteria chapter.
  2. Calls the Database: It sends the request to the database to fetch the raw data. This is the core of the HANA Database Data Retrieval (AMDP) process.
  3. Enriches the Data: It takes the raw data and adds more user-friendly information (like names and descriptions), transforming it from the gt_final structure to the final gt_sfinal structure. This is the focus of the Data Transformation and Enrichment chapter.

Here's a simplified look inside the get_amdp_data subroutine to see how it manages these sub-tasks.

FORM get_amdp_data.

  " 1. Package the user's request for the database.
  DATA(ex_bset) = cl_shdb_seltab=>combine_seltabs(...).
  DATA(ex_acdoca) = cl_shdb_seltab=>combine_seltabs(...).

  " 2. Call the data retrieval expert (AMDP class) to fetch raw data.
  NEW zcl_amdb_fico_tax( )->get_data(
    EXPORTING
      im_qacdoca = ex_acdoca
      im_qbset   = ex_bset
    IMPORTING
      ex_final   = gt_final " <-- Receives raw data
  ).

  " 3. Transform the raw data into the final display format.
  LOOP AT gt_final INTO DATA(gs_final).
    " Move raw data to final structure...
    " Add extra details (names, descriptions)...
    APPEND gs_sfinal TO gt_sfinal.
  ENDLOOP.

ENDFORM.

By bundling all these data-related steps into one subroutine, our main orchestration logic in START-OF-SELECTION remains incredibly clean and simple.

Conclusion​

In this chapter, we met the conductor of our report. We learned that the VAT Report Orchestration is the master process that controls the program's flow.

Key takeaways:

  • The START-OF-SELECTION event block is the main entry point after the user clicks "Execute".
  • Good orchestration involves delegating tasks to specialized helper subroutines (PERFORM).
  • This keeps the main logic clean and makes the program's overall sequence easy to understand: get data, prepare display, show display.

We've seen that the orchestrator calls a powerful data retriever, but we haven't seen how that retriever works its magic. How does it communicate with the super-fast HANA database to get data with incredible speed? That is the subject of our next, exciting chapter.

Next: Chapter 5: HANA Database Data Retrieval (AMDP)

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