Reuse a CAP Java Service

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.

Make sure you stopped your application from the previous tutorial.

1. From the main menu of SAP Business Application Studio, choose Terminal → New Terminal.

2. Before adding the bookstore project, we need to make sure that you are in the projects folder. Both projects (products-service and bookstore) should be placed next to each other. Run the following command in the newly created terminal to go back to the projects folder:

   Shell/Bash Copy

   cd ~/projects

3. Now that you are in the correct folder, run the following command:

   Shell/Bash Copy

   cds init bookstore --add java

4. To open the bookstore project in a new workspace go to File → Open Folder.

5. 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.

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 the package.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.

1. 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:

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   cd ~/projects/bookstore

   This step is optional if you are already in the right directory.

2. Install the reusable service project as npm dependency:

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   npm install $(npm pack ../products-service -s)

   npm pack creates a tarball from the products-service, which is then directly used as a dependency in the bookstore application. Learn more about npm pack.

   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 the products-service project.

3. Install all other packages and simplify the overall dependency structure using npm dedupe:

   Shell/Bash Copy

   npm install && npm dedupe

   If you open the package.json of your bookstore project, you will see a dependency to @sap/capire-products.

   

Now that you have created your bookstore project, you need to define the domain model.

1. Within the ~/projects/bookstore/db folder, create a file called schema.cds.

2. Add the following code to your newly created schema.cds file and make sure you Save the file:

   CDS Copy

   namespace 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;
   }

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The domain model defines four entities:

• Books

• Authors

• Orders

• OrderItems

Again the Currency, cuid and managed types and aspects are imported, as described in the previous tutorial.

In addition, it imports the Products entity, which is reused for the Books entity. To establish the relation between books and authors, the Products entity is extended with an additional association to Authors.

The total element of the Orders entity and the netAmount element of the OrderItems 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.

You will now define the services, that should expose the entities you have defined in your domain model:

1. Within the ~/projects/bookstore/srv folder, create a file called services.cds.

2. Add the following code to the services.cds file and make sure you Save the file:

   CDS Copy

   using { 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;
   }