GraphQL workshop

This project contains 2 microservices: employee and fleet, which are parts of an imaginary Ordina ERP system.

Employee microservice exposes REST endpoints for CRUD operations on the Employee resource. This is a Spring boot application. It has its own embedded H2 database. Employee resource contains carLicencePlate field that can be used as a unique identifier of a company car driven by the employee

Fleet microservice manages Ordina fleet and it exposes the Car resource. As the Employee microservice, Fleet microservice is also a Spring boot application and it also has its own embedded H2 database.

Disclamer. For the sake of simplicity, both microservices were written using Spring Data Rest library and no service discovery is used. The links are hardcoded. Please, do not use this approach in production.

Aim of this hands-on

The aim of this hands-on session is to wrap the REST API into GraphQL by building a the graphql-bff microservice. Most of the code, which is irrelevant to GraphQL is already written for you. Your task is to write the GraphQL functionality.

For this, we are going to use GraphQL Java Kickstart libraries.

Task 1

Add necessary dependencies to pom.xml of the graphql-bff microservice:

• GraphQL Spring boot starter

<dependency>
    <groupId>com.graphql-java-kickstart</groupId>
    <artifactId>graphql-spring-boot-starter</artifactId>
    <version>5.2</version>
</dependency>

This starter will take care of the GraphQL configuration. It will also starts the GraphQl servlet with the default endpoint POST /graphql. All queries should be sent to this endpoint

• GraphiQL Spring boot starter

<dependency>
   <groupId>com.graphql-java-kickstart</groupId>
   <artifactId>graphiql-spring-boot-starter</artifactId>
   <version>5.2</version>
</dependency>

This starter will autoconfigure GraphiQL tool (a la Postman for GraphQL) for the interactive testing. It is accessible at the path /graphiql

• Voyager Spring boot starter

<dependency>
   <groupId>com.graphql-java-kickstart</groupId>
   <artifactId>voyager-spring-boot-starter</artifactId>
   <version>5.2</version>
</dependency>

This starter will autoconfigure Voyager tool for the schema visualization. It is accessible at /voyager and works with Firefox browser

Run mvn clean install from the root pom.xml. The project should compile but the integration tests will fail. Now it is time to start implementing GraphQL.

Task 2

Create schema in the file src/resources/schema.graphqls. This is a default file location. The schema will automatically be picked up and parsed by the GraphQL engine. The schema should contain root queries for getting:

• a list of employees
• a single employee by id
• a list of cars
• a single car by id

and

• a mutation to create a new employee.

When defining fields of the types, use Employee and Car entities from the packages employeeclient and carclient, respectively.

Embed Car type as a field in the Employee type. Do not add Car field in the Employee entity. Do this in the schema only.

When creating the schema you can use examples from the presentation or from the GraphQL website https://graphql.github.io/learn/schema/

Task 3

Implement resolver methods to resolve the root queries in your schema. The method stubs you can find in the class QueryResolver. For this you can used the provided Feign clients with the respective methods. Use normal Spring autowiring, for the client instantiation.

Names of the resolver functions should be the same as the name of the field to be resolved or in may have a prefix "get".

Task 4

Implement the Car resolver method in the class EmployeeResolver. Use car license plate to search for the Car object. Run the respective integration tests

Task 5

Implement the mutation resolver method to add a new employee in the class MutationResolver.

Task 6

Start up all applications one by one from your IDE. The graphql-bff should in this case be run with spring profile local.

Alternatively, start up the whole setup by running:

docker-compose up --build -d

Test the API with the GraphiQL tool that should be accessible at http://localhost:8082/graphiql

Visualize the schema with the Voyager tool by accessing http://localhost:8082/voyager with Firefox

Task 7 (homework, advanced features)

• implement DataLoader instead of the async method to resolve Car in the Employer type
• convert REST endpoints in the employee and fleet microservices into GraphQL endpoints
• implement GraphQL clients in the graphql-bff microservice instead of Feign clients