GENERAL DEFINITION

A CDS view is an infrastructure that defines a data model (similar to a simple view). This data model is created in the database and not on the server. This advantage stems from the fact that a normal view resides in the dictionary and must create a DB connection via the server for data extraction. A CDS view is a simple 'object' that resides directly in the DB and therefore does not require a connection to be managed with it. There are CDS VIEWS with and without parameters, ABAP CDS, and HANA CDS. When selecting fields to extract, keys can be defined by prefixing the field with the keyword key (keys must be contiguous and start from the first field).

ODATA SERVICE

CDS Views can also be used to expose an OData service (otherwise creatable via transaction SEGW) through the annotation @OData.publish: true. Once the view is created, use transaction /IWFND/MAINT_SERVICE to register the service. Test the service using transaction /IWFND/GW_CLIENT.
There might be errors: https://sapyard.com/odata-service-from-cds-annotation-not-working-in-browser-mode/

S4 CLOUD

CDS Views are necessary for extracting data from tables in S4 CLOUD. Standard CDS views are provided, and custom CDS views can be created from these (if you possess the BR_ADMINISTRATOR role).

AUTHORIZATIONS

When a CDS view is created, it has the annotation @AccessControl.authorizationCheck: #NOT_REQUIRED to indicate that no particular privileges are needed to use it. An Access Control must therefore be created. This access control can be used in 3 different ways:

• Full access: No restrictions are applied. Only the view name is entered in the Access Control.
• Literal Conditions: Extraction conditions are imposed to limit the data that is returned.
• PFCG (further details in external links): A role is created that allows users to use only certain functions.

Other methods exist, such as the combination of literal and PFCG, inherited authorizations, and current user authorization.

TRANSLATIONS AND TEXTS

In CDS views, texts can be created: label (with a maximum of 60 characters) and quickinfo (strings).
They are declared with the "@" symbol:

@EndUserText.label: 'Test'
@EndUserText.quickInfo: 'Second test'

These texts can then be translated with transaction SE63, and these translations can be included in a transport with transaction SLXT.
It is possible to access texts and translations dynamically using the class CL_DD_DDL_ANNOTATION_SERVICE method GET_LABEL_4_ELEMENT. With this method, you can specify the language in which you want the texts or allow it to pick the access language (without specifying it).




BASIC SYNTAX

CDS views are parameterized, meaning they also accept input variables (CDS views are case-sensitive). It is important to remember that they also work through aliases, especially when performing join associations. System variables also exist here:

• Case distinction

  • CASE a IS NULL THEN 'err'

• Condition

  • a = b
  • a <> b
  • a > b
  • a < b
  • a >= b
  • a <= b
  • a <= n AND b > n2 (per intervalli)
  • a LIKE b
  • a IS [NOT] NULL

• Arithmetic expressions

• Aggregate expressions

  • MAX
  • MIN
  • AVG
  • SUM
  • COUNT
  • GROUP BY (mandatory)
  • HAVING

• Casting expressions

Note
- System access: (privilege) for using certain functions
- Authorization Objects: These are certain transactions that we can access or not.
- DCL: Data Control Language. Used to control privileges for database operations.
- GRANT: Used to indicate every privilege for a user.
- REVOKE: Used to remove privileges.
- ROLE: Special permissions for specific functions. Maintained by transaction PFCG.