Reuse a CAP Java Service
- How to reuse a CAP project through NPM packages
- How to load sample data using CSV files
- How to use the localized keyword
Now, that your products service is ready to be reused, you will build a bookstore application upon it.
In this tutorial you will create the model and the services of the bookstore application. After that you will initialize the database of your bookstore application with localized example data coming from CSV files.
You will then run your application – still without any custom coding required – and see the localization features of CAP in action.
- Step 1
From the products service that you created in the previous tutorial, we just want to reuse the domain and service models. For the bookstore, which you will develop in this tutorial, we need to create and initialize a bookstore project first.
From the main menu of SAP Business Application Studio, choose Terminal → New Terminal.
Before adding the
bookstore
project, we need to make sure that you are in the projects folder. Both projects (products-service
andbookstore
) should be placed next to each other. Run the following command in the newly created terminal to go back to the projects folder:Shell/BashCopycd ~/projects
Now that you are in the correct folder, run the following command:
Shell/BashCopymvn -B archetype:generate -DarchetypeArtifactId=cds-services-archetype -DarchetypeGroupId=com.sap.cds \ -DarchetypeVersion=RELEASE \ -DgroupId=com.sap.cap -DartifactId=bookstore
To open the bookstore project in a new workspace go to File → Open Folder.
Choose bookstore from the project list and then OK.
If you see a notification asking if you want to synchronize the
Java classpath/configuration
, choose Always.If you have any problem indication for any of the
pom.xml
files yet, don’t worry and ignore them for now.
- Step 2
As the
product-service
should be reused for the bookstore, you need to add a dependency between those two projects. Reusable models can be published as NPM modules and imported through dependencies in thepackage.json
of a project.Make sure that you have followed all the sub-steps in the previous tutorial Set up for reuse before continuing.
First, we need to simulate a release of the
product-service
module, and consume this release in the bookstore application.-
From the main menu of SAP Business Application Studio, choose Terminal → New Terminal. Change into the bookstore directory by executing the following command in the terminal:
Shell/BashCopycd ~/projects/bookstore
This step is optional if you are already in the right directory.
-
Install the reusable service project as npm dependency:
Shell/BashCopynpm install $(npm pack ../products-service -s)
npm pack
creates a tarball from theproducts-service
, which is then directly used as a dependency in the bookstore application. More aboutnpm pack
: https://docs.npmjs.com/cli-commands/pack.html.You will find a
sap-capire-products-1.0.0.tgz
in the root folder of the bookstore project, which is the tarball file of theproducts-service
project. -
Install all other packages and simplify the overall dependency structure
npm dedupe
:Shell/BashCopynpm install && npm dedupe
If you open the
package.json
of your bookstore project, you will see a dependency to@sap/capire-products
.
What technology is used to reuse services between different applications in CAP?
-
- Step 3
Now that you have created your bookstore project, you need to define the domain model.
-
Within the
~/projects/bookstore/db
folder, create a file calledschema.cds
. -
Add the following code to your newly created
schema.cds
file and make sure you Save the file:CDSCopynamespace sap.capire.bookstore; using { Currency, cuid, managed } from '@sap/cds/common'; using { sap.capire.products.Products } from '@sap/capire-products'; entity Books as projection on Products; extend Products with { // Note: we map Books to Products to allow reusing AdminService as is author : Association to Authors; } entity Authors : cuid { firstname : String(111); lastname : String(111); books : Association to many Books on books.author = $self; } @Capabilities.Updatable: false entity Orders : cuid, managed { items : Composition of many OrderItems on items.parent = $self; total : Decimal(9,2) @readonly; currency : Currency; } @Capabilities.Updatable: false entity OrderItems : cuid { parent : Association to Orders not null; book_ID : UUID; amount : Integer; netAmount : Decimal(9,2) @readonly; }
The domain model defines four entities:
-
Books
-
Authors
-
Orders
-
OrderItems
Again the
Currency
,cuid
andmanaged
types and aspects are imported, as described in the previous tutorial.In addition, it imports the
Products
entity, which is reused for theBooks
entity. To establish the relation between books and authors, theProducts
entity is extended with an additional association toAuthors
.The
total
element of theOrders
entity and thenetAmount
element of theOrderItems
entity are annotated with@readonly
. This means the value of these elements cannot be set by a client. The value is calculated by custom code. You will implement this custom code in a later tutorial. Both of these entities are also annotated with@Capabilities.Updatable: false
, which means that they cannot be updated, only created and deleted. -
- Step 4
You will now define the services, that should expose the entities you have defined in your domain model:
Within the
~/projects/bookstore/srv
folder, create a file calledservices.cds
.Add the following code to the
services.cds
file and make sure you Save the file:CDSCopyusing { sap.capire.bookstore as db } from '../db/schema'; // Define Books Service service BooksService { @readonly entity Books as projection on db.Books { *, category as genre } excluding { category, createdBy, createdAt, modifiedBy, modifiedAt }; @readonly entity Authors as projection on db.Authors; } // Define Orders Service service OrdersService { entity Orders as projection on db.Orders; entity OrderItems as projection on db.OrderItems; } // Reuse Admin Service using { AdminService } from '@sap/capire-products'; extend service AdminService with { entity Authors as projection on db.Authors; }
The
services.cds
file defines three services:BooksService
OrdersService
AdminService
The
BooksService
is used to provide a read-only view on theBooks
andAuthors
data. Modifications of these entities isn’t possible via this service.The
OrdersService
allows to view, create, and delete orders.The
AdminService
is reused from the products service. But we’ve added theAuthors
entity to it. It can be used to create, update, and delete products and authors.It’s considered best practice to define services with a single use-case in mind. For example, the
AdminService
is meant for administrating Products, Authors and Categories, while theBooksService
is meant for exposing a catalog of books and authors, hiding administrative data such as creation and modification times from the end user. - Step 5
After defining the domain model and the services that you want to expose, you could already start your application. But first, we’d like to add some sample data to your database. To do so, we’ll need to use some CSV files:
From your
bookstore
project, right-click thedb
folder and choose New Folder. Call the folderdata
.Go to the data folder by running the following command in the terminal:
Shell/BashCopycd ~/projects/bookstore/db/data
Download CSV data for the Authors entity by running the following command in the terminal:
Shell/BashCopycurl https://raw.githubusercontent.com/SAP-samples/cloud-cap-samples/CAA160-final/bookstore/db/data/sap.capire.bookstore-Authors.csv -O
Download CSV data for the Books entity by running the following command in the terminal:
Shell/BashCopycurl https://raw.githubusercontent.com/SAP-samples/cloud-cap-samples/CAA160-final/bookstore/db/data/sap.capire.bookstore-Books.csv -O
Rename it with the following command:
Shell/BashCopymv sap.capire.bookstore-Books.csv sap.capire.products-Products.csv
Download translated CSV data for the Books entity by running the following command in the terminal:
Shell/BashCopycurl https://raw.githubusercontent.com/SAP-samples/cloud-cap-samples/CAA160-final/bookstore/db/data/sap.capire.bookstore-Books_texts.csv -O
Rename it with the following command:
Shell/BashCopymv sap.capire.bookstore-Books_texts.csv sap.capire.products-Products_texts.csv
Download CSV data for the Categories entity by running the following command in the terminal:
Shell/BashCopycurl https://raw.githubusercontent.com/SAP-samples/cloud-cap-samples/CAA160-final/bookstore/db/data/sap.capire.products-Categories.csv -O
You should now have 4 CSV files with sample data. The files deliver initial data for the service that we reuse and for one entity that we created in the
bookstore
service:sap.capire.products-Categories.csv
sap.capire.products-Products.csv
sap.capire.products-Products_texts.csv
sap.capire.bookstore-Authors.csv
The name of the CSV has to match the pattern [namespace]-[entity name] exactly otherwise the the application will fail to start.
- Step 6
In the terminal, go to the root of the bookstore project:
Shell/BashCopycd ~/projects/bookstore
Ensure that you have stopped all previously running applications (including the
products-service
application) by usingCTRL+C
.In case you forgot to stop the
products-service
application and the tab in which it was started is no longer opened you can runkillall mvn
in the terminal to ensure it’s terminated.Start the application by running:
Shell/BashCopymvn spring-boot:run
You will see a pop-up in the SAP Business Application Studio. Choose Open in a New Tab.
When you open the URL in a new tab, you will see a welcome page. To see the books data click on Books directly from the welcome page.
Instead of clicking on the Books entry on the welcome page, you could simple add
odata/v4/BooksService/Books
to the URL.To read the localized German example data, append the query parameter
?sap-language=de
to the URL. For example,<APP_URL>/odata/v4/BooksService/Books?sap-language=de
. Try to switch the language between German (de
) and English (en
).
Great Job! You have successfully developed the bookstore application and reused your products service from the previous tutorial.
In the next tutorial you will extend this application with custom code, to calculate the
total
andnetAmount
elements of theOrders
andOrderItems
entity. In addition, you will add custom code that will decrease the stock in the Books entity whenever an order is created.