SAP Cloud Application Programming Model Getting Started (CAP)

This article describes how to get started with building Cloud Application Programming Model (CAP) projects and according artefacts with Core Data Services (CDS).

For local native development see SAP HANA Local Native Development

Sources and Further Reading

Description	URL	Comment
All-in-one Quick Start	https://github.com/SAP-samples/cloud-cap-walkthroughs/blob/master/exercises-node/intro/README.md
Back to basics SAP Cloud Application Programming Model (CAP)	https://www.youtube.com/playlist?list=PL6RpkC85SLQBHPdfHQ0Ry2TMdsT-muECxhttps://github.com/qmacro/capb2b	SAP Developers YouTube Playlist and GitHub Repository
Qmacro / DJ Adams	https://qmacro.org/tags/cap/
Qmacro @ SAP Community	https://community.sap.com/t5/user/viewprofilepage/user-id/53
SAP CAP Documentation	https://cap.cloud.sap/
SAP CAP Sample Repositories	https://github.com/SAP-samples/cloud-cap-samples	Use opensap*-Branches
GitHub Repositories of CAP and Fiori Showcases	https://github.com/SAP-samples/cap-sflighthttps://github.com/SAP-samples/fiori-elements-feature-showcase
ABAP Freak Show Ep. 1 - HANA Cloud and the Business Application Studio	https://www.youtube.com/watch?v=a3WPQwmpbvI&list=PLoc6uc3ML1JR38-V46qhmGIKG07nXwO6X&index=71

Installation of Prerequisites

Relevant Tools from SAP

npm i -g @sap/cds
npm i -g @sap/cds-dk

Additional 3rd Party Tools

npm i -g hana-cli

Setup of CAP Projects

Create CDS Project

cds init bookshop

or

cds init MyCDSProject --add hana, mta

Download and install dependencies:

npm install

Start Service

cds watch
cds w

This also monitors changes to the underlying files and restarts when a file has changed.

Prevent Reloading

To prevent reloading the service, for example when saving temporary files in the project directory, save the files in one of the directoryies which are excluded from monitoring for file changes, which are:

• _out
• node_modules
• @types
• @cds-models

For more details see: https://qmacro.org/blog/posts/2024/04/10/avoid-design-time-cap-server-restarts-when-maintaining-local-data-files/

Add Persistency to CDS

In case of SQLite first install SQLite3 packages by executing in the root of the project folder:

npm i sqlite3 -D

Deploy data model to different database types:

cds deploy

This deploys the cds entity models and csv files to the database specified in package.json in section cds.requires.db. This should look like this:

{ "cds": 
    { "requires": {
       "db": {
          "kind": "sqlite",
        "credentials": { "url": "db.sqlite" } 
            }
        }
    }
}

For more explainations see for SQLite see https://cap.cloud.sap/docs/guides/databases-sqlite

cds deploy --to sqlite          # Deploys to sqlite.db
cds deploy --to sqlite:my.db    # Deploys to my.db
cds deploy --to hana            # Deploys to HDI container on HANA
                                # (Requires Cloud Foundry login)    

This does not update the package.json secion cds.requires.db any more as opposed to older cds versions.

In order to see the actual created SQL statements:

cds compile srv/cat-service.cds --to sql     # Creates SQL statements
cds compile srv/cat-service.cds --to hana    # Creates hdbcds or hdbtable/hdbview artefacts

When deployed to SQLite database use this statement to view the database:

sqlite3 my.db -cmd .dump

Create CSV header files in db location (by default db/data) for modeled entities:

cds add data

Deployment to SAP Business Technology Platform (BTP)

Login to CF space:

cf login

Build Deployment Package

cds add hana

package.json needs to contain "kind": "hana". (really? - for which CF / HANA Cloud Version?)

Also when deploying to BTP which is internally HANA 4.0 "deploy-format": "hdbtable" has to be set and hdi-deploy should be at least version 4. Example:

{
    ...
    "devDependencies": {
        "@sap/hdi-deploy": "^4"
    },
    ...
    "cds": {
        "hana": {
            "deploy-format": "hdbtable"
        },
        "requires": {
            "db": {
                "model": [
                    "db",
                    "srv"
                ],
                "kind": "hana"
            }
        }
    }
}

Deploy via Cloud Foundry CLI

Build the deployment artifacts:

cds build/all
cds build --production         # Only production profile?

Create a hana service for the hdi-container. The stated hdi-container name must correlate to the services-name in /gen/db/src/manifest.yaml.

cf create-service hana hdi-shared <app-db-hdi-container>

Now push the DB deployer application and also the actual service application:

cf push -f gen/db
cf push -f gen/srv --random-route

Deploy via MTA

Install MTA Build Tool

npm install -g mbt

Generate MTA project descriptor file mta.yaml and build MTA archive:

cds add mta
mbt build

Deploy MTA archive to CF space:

cf deploy mta_archives/<buildmta>.mtar

Troubleshooting

Real-time output of CF services can be displayed in BAS terminal with

cf logs <appname>

CDS Commands Cheatsheet

Noteworthy Commands

Command	Description
cds env	Displays the effective configuration...
cds env ls	... in .properties format
cds compile services.cds	Compile JSON-like database structure
cds compile services.cds | jq	dto, but in actual JSON
cds compile services.cds --to sql	Compile SQL statements from CDS
cds compile services.cds --to edmx	Compile EDMX file (metadata) from CDS
cds compile services.cds --to csn	Output CSN = Internal CDS Schema Notation...
cds compile services.cds --to csn | jq '.definitions | keys'	... and process output with JSON processor by extracting keys of definition nodes
cds compile schema.cds --to yaml	Output Yaml of database schema
cds compile services.cds --to yaml	Output Yaml of all services including their db schema
cds add data	Create CSV header files in db location (by default db/data) for modeled entities

Using CDS REPL & JavaScript APIs

cds r
cds repl

This launches an read-eval-print-loop which can be used as an interactive playground to experiment with CDS' JavaScript APIs.

API	Description
cds.utils.uuid()	Returns an UUID

Accessing Services from Command Line

Reading from Services

Read output of services via curl and pipe it through jq for nicer formatting:

curl -s 'localhost:4004/odata/v4/bookshop/Orders' | jq

Output (example for Bookshop repo):

{
  "@odata.context": "$metadata#Orders",
  "value": [
    {
      "ID": "6091d4ab-650e-4afa-90bb-163305e473a2",
      "comment": "second order"
    },
    {
      "ID": "ac5aeb9f-c7cd-4f52-ab4a-9c0313ded402",
      "comment": "first order"
    }
  ]
}

Deep Insert into Service with POST

For performing a deep insert we first need a at least two level deep structure.

The following neworder.json file with a two-level deep structure is given:

{
    "comment": "New Order",
    "Items": [
            {
                "pos": 1,
                "quantity": 10
            },
            {
                "pos": 2,
                "quantity": 20
            }
        ]
}

To perform the deep insert put the json file into the service by utilizing curl. The filename needs to be prefixed with a @. As we are connecting to a web service we also need to add a header and specify the content type, in this case application/json:

curl --verbose --data @neworder.json --header 'content-type: application/json' --url 'localhost:4004/odata/v4/bookshop/Orders'

By default curl with parameter --data uses the POST method. For more details on the HTTP methods see Notable RFCs Section HTTP Methods GET, POST, PUT, DELETE

We should receive an answer that is similar to the following one in that we are connected to localhost, and we posted to odata service and that the HTTP code was 201 Created:

*   Trying 127.0.0.1:4004...
* Connected to localhost (127.0.0.1) port 4004 (#0)
> POST /odata/v4/bookshop/Orders HTTP/1.1
> Host: localhost:4004
> User-Agent: curl/7.74.0
> Accept: */*
> content-type: application/json
> Content-Length: 193
> 
* upload completely sent off: 193 out of 193 bytes
* Mark bundle as not supporting multiuse
< HTTP/1.1 201 Created
< X-Powered-By: Express
< X-Correlation-ID: 4eee1d5a-5b43-4577-8257-a99b026a0c43
< OData-Version: 4.0
< content-type: application/json;odata.metadata=minimal
< Location: Orders(9416b371-2355-402a-b06d-34f5b2c61704)
< Date: Sat, 20 Apr 2024 12:23:52 GMT
< Connection: keep-alive
< Keep-Alive: timeout=5
< Content-Length: 280
< 
* Connection #0 to host localhost left intact
{"@odata.context":"$metadata#Orders(Items())/$entity","ID":"9416b371-2355-402a-b06d-34f5b2c61704","comment":"New Order","Items":[{"parent_ID":"9416b371-2355-402a-b06d-34f5b2c61704","pos":1,"quantity":10},{"parent_ID":"9416b371-2355-402a-b06d-34f5b2c61704","pos":2,"quantity":20}]}

Update Records via Service with PATCH

Following up the deep insert example above let's assume we want to update the Order with comment New Order. For this we create a neworder-update.json with a different content, i.e.:

{
  "comment": "New Order",
  "Items": [
          {
              "pos": 1,
              "quantity": 1000
          }
      ]
}

To perform the update we need to refer to the ID of the previously created Order to have this one updated. This happens by using the ID 9416b371-2355-402a-b06d-34f5b2c61704 from the server response above and adding it to the url after Order in parentheses:

curl -X PATCH --verbose --data @neworder-update.json --header 'content-type: application/json' --url 'localhost:4004/odata/v4/bookshop/Orders(9416b371-2355-402a-b06d-34f5b2c61704)' | jq .

The expected result is HTTP code 200 OK:

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0*   Trying 127.0.0.1:4004...
* Connected to localhost (127.0.0.1) port 4004 (#0)
> PATCH /odata/v4/bookshop/Orders(9416b371-2355-402a-b06d-34f5b2c61704) HTTP/1.1
> Host: localhost:4004
> User-Agent: curl/7.74.0
> Accept: */*
> content-type: application/json
> Content-Length: 121
> 
} [121 bytes data]
* upload completely sent off: 121 out of 121 bytes
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< X-Powered-By: Express
< X-Correlation-ID: 9a21bb8f-cfcc-4641-bc68-2f1bcbb7d5a8
< OData-Version: 4.0
< content-type: application/json;odata.metadata=minimal
< Date: Sat, 20 Apr 2024 12:34:13 GMT
< Connection: keep-alive
< Keep-Alive: timeout=5
< Content-Length: 198
< 
{ [198 bytes data]
100   319  100   198  100   121  19800  12100 --:--:-- --:--:-- --:--:-- 31900
* Connection #0 to host localhost left intact
{
  "@odata.context": "$metadata#Orders/$entity",
  "ID": "9416b371-2355-402a-b06d-34f5b2c61704",
  "comment": "New Order",
  "Items": [
    {
      "parent_ID": "9416b371-2355-402a-b06d-34f5b2c61704",
      "pos": 1,
      "quantity": 1000
    }
  ]
}

Check the results with queueing the service again:

curl -s 'localhost:4004/odata/v4/bookshop/Orders?$expand=Items' | jq

{
  "@odata.context": "$metadata#Orders(Items())",
  "value": [
    {
      ...
    },
    {
      "ID": "9416b371-2355-402a-b06d-34f5b2c61704",
      "comment": "New Order",
      "Items": [
        {
          "parent_ID": "9416b371-2355-402a-b06d-34f5b2c61704",
          "pos": 1,
          "quantity": 1000
        }
      ]
    },
    {
      ...
    }
  ]
}