SAP Developer Challenge - SAP Cloud Application Programming Model (Week 3)

[nicoschoenteich]

Please note that this challenge is closed. The deadline for receiving a badge upon successful completion has passed. Check out this new challenge for the month of August.

Welcome to the third week of this month's SAP Developer Challenge. This week we are going to learn how to use event handlers with the SAP Cloud Application Programming Model.

If you haven't read the announcement blog post for this challenge, please head over and do so. This week's challenge builds on top of previous two challenges, which you should have completed before starting with this one.

The Challenge

After moving to the SAP Business Application Studio and adding some sample data to our application last week, it's now time to explore some more features and capabilities of the SAP Cloud Application Programming Model. One of those is event handling, which will be our focus for this week.

Let's say we would like to enhance our application by automatically populating a new data field for the entity Holes. We would like to know what score a player scored on a hole, but not as a number, rather as one of the following strings: "birdie", "par", "bogey" (and a few more, see table below). These terms are frequently used in golf to describe the score a player scored on a hole in relation to the hole's par (par = expected score from a professional player). Let's say it took the player 4 shots to get the ball into the hole on a par 4 - that is a par. If it took the player only 3 shots on that same hole - that would be a birdie. See the table below for all mappings.

The described requirement is a perfect use case for event handling in CAP. As described in the documentation, calculated fields should be pre-calculated whenever a new entry is written into the database (instead of calculating on every read operation). This means we need a custom event handler for the CREATE operation on the Holes entity. 

This is what you have to do to successfully complete this week's challenge:

1. Create a new property result: String; in the schema definition of the Holes entity. This is where we will store "par", "birdie", "bogey" etc..

2. Read about custom logic and event handlers  in the CAP documentation. Also read about implementing services in CAP Node.js.

3. Create a new file cat-service.js in the srv/ directory, or give this new file another name and use the @impl annotation.

4. Register an event handler on the CREATE operation on the Holes entity.

5. In the event handler, read the req.data.score and req.data.par properties. Then add some custom logic that calculates and fills the new req.data.result property so it represents the following mappings:

  

Score in relation to par	String
score - par = -3	albatross
score - par = -2	eagle
score - par = -1	birdie
score - par = 0	par
score - par = +1	bogey
score - par = +2	double bogey
score - par = +3	triple bogey
score = 1	hole in one

6. Don't forget to return next()  at the end of your event handler to resume the standard event processing of CAP.

7.  Test your custom event handler by creating a new test.http file and pasting the following code:

POST http://localhost:4004/browse/Holes
Content-Type: application/json

{
    "score": 3,
    "par": 4
}​

8. Your editor (SAP Business Application Studio or VS Code) should recognize the .http file ending and display a little "Send Request" button (if not, you might have to install this extension).

9. Send the test request and inspect the result - hopefully it contains "birdie" as a result.

10. Feel free to test and play around with other requests and values.

11. Share a screen shot of your editor so that we can see the test request being sent and the results field being populated. It should look something like this:

Resources

We have gathered a few helpful resources for this week's challenge. Feel free to use the comments sections if you have question or need help.

• Custom logic and event handlers
• Implementing services (also contains information about event handlers)
• Calculated fields 

Good luck and happy learning!

[vmecko]

Hello, here is my result:

[nicoschoenteich]

Well done ✅

[alina-balysh]

Hello! This is my submission  for this week:

[nicoschoenteich]

Well done ✅

[JohnPaulLiberal]

Hi all!

My submission for this week's challenge:

Thanks for this challenge, @nicoschoenteich.

[nicoschoenteich]

Well done ✅

[MadhavKumar]

Hi @nicoschoenteich,

Sharing Week3 Submission snapshot-

Thank You,

Madhav Kumar

[nicoschoenteich]

Well done ✅

[jdm]

Week 3 submission:

[nicoschoenteich]

Well done ✅

[Geeth]

Hi Nicolai, 

I hope this is fine.

[nicoschoenteich]

Well done ✅

[Cmdd]

Third week submission

[nicoschoenteich]

Well done ✅

[Ruthiel]

Hello!
Here my submission for week 3:

[nicoschoenteich]

Well done ✅

[former_member14975]

Here is my week 3 submission.

[nicoschoenteich]

Well done ✅

[johna69]

 Here are my results:

[nicoschoenteich]

Well done ✅

[MeriemSouissi]

My submission week 3

[nicoschoenteich]

Well done ✅

[andrew_chiam]

Week 3 submission for your verification 😃

[nicoschoenteich]

Well done ✅

[wawowrt]

This is my submission for Week 3. 😊

[nicoschoenteich]

Well done ✅

[cd_winc]

Hi Nico, 

Here is my submission:

but why the request doesn't work for 

POST http://localhost:4004/browse/Holes

it only works for 

POST http://localhost:4004/catalog/Holes

[nicoschoenteich]

Well done ✅

The path depends on what you specified for your service in the service definition file. The template had /browse as a path, but in case you removed that line the service CatalogService gets resolved to /catalog automatically (removing "service" from the name).

[harsh_itaverma]

Got "Birdie" 🕊

[nicoschoenteich]

Well done ✅

[andrew_mak]

Hi, my week 3 submission.

browse Holes

Thanks.

[nicoschoenteich]

Well done ✅

[satya-dev]

My submission.