SAP recommends that you eliminate the following types of legacy code when you review modifications as part of an SAP S/4HANA system conversion:

Code that now is identical to a standard SAP object. This type of code is redundant and unnecessary, as it does not provide any additional functionality or customization. It can also cause conflicts or errors during the system conversion, as the standard SAP object may have changed or been replaced in SAP S/4HANA. Therefore, you should delete this type of code and use the standard SAP object instead.

Code that can be redesigned as a key user extension. This type of code is usually related to UI or business logic adaptations that can be achieved using the in-app tools provided by SAP S/4HANA. By redesigning this type of code as a key user extension, you can simplify and standardize your code base, reduce maintenance efforts, and avoid compatibility issues during the system conversion. Therefore, you should migrate this type of code to the key user extensibility framework and delete the original code.

The other types of legacy code are not recommended to be eliminated, as they may still be relevant or necessary for your business processes. However, you should still review and adjust them according to the SAP S/4HANA simplification items and best practices. These types of code are:

Code that supports a critical business process. This type of code is essential for your business operations and cannot be easily replaced or removed. However, you should check if this type of code is compatible with SAP S/4HANA, and if not, you should adapt it accordingly. You should also consider if this type of code can be optimized or enhanced using the new features and capabilities of SAP S/4HANA.

Code that has less than 10% usage according to usage statistics. This type of code is rarely used and may not be worth maintaining or converting. However, you should not delete this type of code without verifying its relevance and impact on your business processes. You should also consider if this type of code can be replaced or consolidated with other code that has higher usage or better performance.

A metadata extension is a RESTful Application Programming object that can be used to organize the display of fields in an app. A metadata extension is a CDS view that annotates another CDS view with UI annotations, such as labels, icons, or facets. These annotations define how the data should be presented in the app, such as which fields should be shown on the object page, which fields should be editable, or which fields should be used for filtering or sorting.A metadata extension can also be used to add custom actions or validations to the app12.Reference:1:Refine the Object Page with Annotations | SAP Tutorials2:ABAP RAP : Enabling custom actions with a dialog for additional input fields | SAP Blogs

When processing a loop with the statement DO... ENDDO, the system variable that contains the implicit loop counter is sy-index. The loop counter is a numeric value that indicates how many times the loop has been executed. The loop counter is initialized to 1 before the first execution of the loop and is incremented by 1 after each execution. The loop counter can be used to control the number of loop iterations or to access the loop elements by index.The loop counter can also be accessed or modified within the loop body, but this is not recommended as it may cause unexpected results or errors1.

For example, the following code snippet uses the loop counter sy-index to display the numbers from 1 to 10:

DO 10 TIMES. WRITE: / sy-index. ENDDO.

The output of this code is:

1 2 3 4 5 6 7 8 9 10

You would use Access Controls with CDS Views for the following reasons:

A . Only the data corresponding to the user's authorization is transferred from the database to the application layer. This is true because Access Controls allow you to define CDS roles that specify the authorization conditions for accessing a CDS view. The CDS roles are evaluated for every user at runtime and the system automatically adds the restrictions to the selection conditions of the CDS view. This ensures that only the data that the user is authorized to see is read from the database and transferred to the application layer.This improves the security and the performance of the data access1.

C . You do not have to remember to implement AUTHORITY CHECK statements. This is true because Access Controls provide a declarative and centralized way of defining the authorization logic for a CDS view. You do not have to write any procedural code or use the AUTHORITY CHECK statement to check the user's authorization for each data source or field.The system handles the authorization check automatically and transparently for you2.

The following reasons are not valid for using Access Controls with CDS Views:

B . The system field sy-subrc is set, giving you the result of the authorization check. This is false because the system field sy-subrc is not used by Access Controls. The sy-subrc field is used by the AUTHORITY CHECK statement to indicate the result of the authorization check, but Access Controls do not use this statement.Instead, Access Controls use CDS roles to filter the data according to the user's authorization2.

D . All of the data from the data sources is loaded into your application automatically and filtered there according to the user's authorization. This is false because Access Controls do not load all the data from the data sources into the application layer. Access Controls filter the data at the database layer, where the data resides, and only transfer the data that the user is authorized to see to the application layer.This reduces the data transfer and the memory consumption of the application layer1.