Lesson 2 Practice — Airport CDS Model

In Lesson 1 practice, the airport architecture was:

Runner
  ↓
Airport Reader
  ↓
ABAP SQL
  ↓
/DMO/AIRPORT

This assignment changes it to:

Runner
  ↓
Airport Reader
  ↓
ABAP SQL
  ↓
ZI_AIRPORT_###
  ↓
/DMO/AIRPORT

You will create the CDS model and refactor the Reader while keeping the Reader's public responsibility clear.

This assignment does not include the complete solution.

---

Objects

You will work with:

ZI_AIRPORT_###
ZCL_AIRPORT_READER_###
ZCL_SQL_L01_PRACTICE_###

If you completed the Lesson 1 Airport practice, reuse the existing Reader and Runner.

If those objects do not exist, create them using the Reader/Runner structure from Lesson 1 before completing the refactor sections.

Replace ###

Use your own student/group suffix in every object name.

---

Part 1 — Review the persistence source

Open:

/DMO/AIRPORT

Confirm these fields:

airport_id
name
city
country

Open Data Preview.

Record one airport ID and one country that exist in your system.

Airport ID:
Country:

---

Part 2 — Design the CDS model

Your CDS entity must expose:

Persistence field	CDS element
airport_id	AirportId
name	Name
city	City
country	Country

Requirements:

• entity name: ZI_AIRPORT_###;
• source: /DMO/AIRPORT;
• source alias: Airport;
• AirportId is the CDS key;
• include a readable end-user label;
• set the tutorial entity's CDS authorization-check annotation to #NOT_REQUIRED.

Before writing code, sketch the model:

/DMO/AIRPORT
      ↓
ZI_AIRPORT_###
      ├─ AirportId
      ├─ Name
      ├─ City
      └─ Country

---

Part 3 — Create the Data Definition

In ADT:

1. select your package;
2. right-click;
3. choose:

New
  → Other ABAP Repository Object
  → Core Data Services
  → Data Definition

4. enter:

Name:        ZI_AIRPORT_###
Description: Lesson 2 - Airport CDS

5. if Referenced Object is available, enter:

/DMO/AIRPORT

6. select the course transport request if required;
7. choose a CDS View Entity template;
8. confirm the generated source uses:

define view entity

9. finish the wizard.

---

Part 4 — Implement the CDS View Entity

Write the CDS entity.

Required concepts:

@AccessControl.authorizationCheck
@EndUserText.label
define view entity
as select from
source alias
key
element aliases

Hint — Header and source

@AccessControl.authorizationCheck: #NOT_REQUIRED
@EndUserText.label: 'Airport'

define view entity ZI_Airport_###
  as select from /dmo/airport as Airport
{
  ...
}

Hint — Key

The first element begins:

key Airport.airport_id as AirportId,

Do not open the lesson companion until you have made a serious attempt.

---

Part 5 — Use ADT code completion

Inside the element list:

1. type:

Airport.

2. press:

Ctrl + Space

3. use the completion list to add at least one source field.

This task is part of the assignment: use the tooling rather than typing every technical name from memory.

---

Part 6 — Check and activate

Run a syntax check:

Ctrl + F2

Fix all syntax errors.

Activate:

Ctrl + F3

The Data Definition must be active before the next tasks.

---

Part 7 — CDS Data Preview

With the cursor in the CDS source, press:

F8

Confirm the visible columns are:

AirportId
Name
City
Country

Answer:

1. Which names are visible: persistence names or CDS element names?

2. Did creating the CDS entity create a second copy of the airport records?

---

Part 8 — SQL Console

Open SQL Console.

Write a query against:

ZI_AIRPORT_###

Requirements:

• select AirportId, Name, City, and Country;
• sort by AirportId;
• do not query /DMO/AIRPORT for this task.

Then add a filter using the country value recorded in Part 1.

The SQL Console result should use the CDS element names.

---

Part 9 — Inspect the existing Airport Reader

Open:

ZCL_AIRPORT_READER_###

Find the SQL in:

GET_ALL
GET_BY_COUNTRY
GET_BY_ID

Before modifying it, answer:

Which data source does the Reader currently use?

________________________

Which data source should it use after this assignment?

________________________

---

Part 10 — Refactor GET_ALL

Change the Reader so GET_ALL selects from:

ZI_AIRPORT_###

The Reader's existing public result structure uses names such as:

airport_id
name
city
country

The CDS entity exposes:

AirportId
Name
City
Country

Use ABAP SQL aliases so the Reader can keep its existing result contract.

Requirements:

• source is ZI_AIRPORT_###;
• fields come from the CDS entity;
• result aliases match the Reader's existing structure;
• order by AirportId;
• no direct /DMO/AIRPORT SELECT remains in GET_ALL.

Hint

One field mapping has this form:

AirportId AS airport_id

---

Part 11 — Refactor GET_BY_COUNTRY

Change GET_BY_COUNTRY.

Requirements:

• source is ZI_AIRPORT_###;
• the WHERE condition uses the CDS element Country;
• the ABAP host variable still uses @;
• output aliases preserve the Reader's existing result structure;
• order by AirportId.

---

Part 12 — Refactor GET_BY_ID

Change GET_BY_ID.

Requirements:

• use SELECT SINGLE;
• source is ZI_AIRPORT_###;
• use CDS element AirportId in the WHERE;
• map CDS result elements to the Reader's existing result structure;
• preserve the existing found handling.

---

Part 13 — Run the existing Runner

Open:

ZCL_SQL_L01_PRACTICE_###

Run it.

The Runner should continue calling the Airport Reader.

Confirm that:

• all-airports output still works;
• country filtering still works;
• lookup by airport ID still works;
• not-found handling still works.

Do not move the SQL into the Runner.

---

Part 14 — Prove the architecture

Draw or write the final dependency chain:

____________________
        ↓
____________________
        ↓
____________________
        ↓
____________________

The four layers should identify:

Runner
Reader
CDS View Entity
Database table

---

Part 15 — Reasoning questions

Answer in your own words.

1. What problem does the CDS layer solve that a direct table SELECT does not?

2. What is the difference between the Data Definition and the CDS View Entity?

3. What is the purpose of the source alias Airport?

4. Why does the CDS model expose AirportId instead of forcing every consumer to use airport_id?

5. What does the CDS key mean?

6. Why does the Reader use:

AirportId AS airport_id

when reading the CDS entity?

7. Why can the Runner remain unchanged when the Reader changes from /DMO/AIRPORT to ZI_AIRPORT_###?

8. What is the difference between Data Preview, SQL Console, and the Reader?

9. Why is the Reader still useful after CDS has been introduced?

10. Why should new course CDS examples use define view entity instead of the older define view?

---

Optional challenge — Restrict the CDS model

Create a second CDS View Entity:

ZI_AIRPORT_BASIC_###

Expose only:

AirportId
Name
Country

Do not expose City.

Activate it and compare:

/DMO/AIRPORT Data Preview
ZI_AIRPORT_### Data Preview
ZI_AIRPORT_BASIC_### Data Preview

Answer:

Which layer decides what a CDS consumer can see?

---

Submission checklist

• ZI_AIRPORT_### exists in your package.
• It uses define view entity.
• Its source is /DMO/AIRPORT.
• It uses the Airport source alias.
• AirportId is marked as the CDS key.
• Name, City, and Country are exposed.
• The Data Definition activates.
• CDS Data Preview works.
• SQL Console successfully queries the CDS entity.
• GET_ALL now reads ZI_AIRPORT_###.
• GET_BY_COUNTRY now reads ZI_AIRPORT_###.
• GET_BY_ID now reads ZI_AIRPORT_###.
• The Reader's public result contract still works.
• The Runner contains no direct airport SQL.
• The existing Runner still executes successfully.
• The reasoning questions are answered.

---

Useful ADT shortcuts

Action	Shortcut
Open ABAP Development Object	Ctrl + Shift + A
Code completion	Ctrl + Space
Syntax check	Ctrl + F2
Activate current object	Ctrl + F3
Activate all inactive objects	Ctrl + Shift + F3
CDS Data Preview	F8
Run console class	F9
Format source	Shift + F1