Trying out a federation with two external endpoint services

[shamin2021]

I have two sub graphs as separate services running on two endpoints

1. http://localhost:8080/graphql - show subgraph
2. http://localhost:8081/graphql - reviews subgraph
   For these services I have cloned and upped the two services in the popular Federation Example DGS [https://github.com/Netflix/dgs-federation-example]

In my simple federated gateway creation using orchestrator I have created two service provider classes for the two services
1.Show

class ShowsService implements ServiceProvider {

    private String endpoint;
    private QueryExecutor queryExecutor;
    private String schema;

    public ShowsService(String endpoint, WebClient webClient) {
        this.endpoint = endpoint;
        this.queryExecutor = (QueryExecutor) new WebClientQueryExecutor(webClient, endpoint);

        System.out.println(queryExecutor.toString());
        try {
            this.schema = readFileAsString("src/main/resources/Shows.graphqls");
        } catch (Exception e) {
            throw new RuntimeException("Error reading schema file", e);
        }
    }

    @Override
    public String getNameSpace() { return "Showsss"; }

    @Override
    public ServiceType getSeviceType() {
        return ServiceType.FEDERATION_SUBGRAPH;
    }

    @Override
    public Map<String, String> sdlFiles() { return ImmutableMap.of("schema.graphqls", schema); }

    @Override
    public CompletableFuture<Map<String, Object>> query(final ExecutionInput executionInput,
                                                        final GraphQLContext context) {
        return queryExecutor.query(executionInput, context);
    }

    public static String readFileAsString(String filePath) throws Exception {
        Path path = Paths.get(filePath);
        byte[] bytes = Files.readAllBytes(path);
        String content = new String(bytes, StandardCharsets.UTF_8);
        return content;
    }
}

2.Review

class ReviewsService implements ServiceProvider {

    private String endpoint;
    private QueryExecutor queryExecutor;
    private String schema;

    public ReviewsService(String endpoint, WebClient webClient) {
        this.endpoint = endpoint;
        this.queryExecutor = (QueryExecutor) new WebClientQueryExecutor(webClient, endpoint);

        try {
            this.schema = readFileAsString("src/main/resources/Reviews.graphqls");
        } catch (Exception e) {
            throw new RuntimeException("Error reading schema file", e);
        }
    }

    @Override
    public String getNameSpace() { return "reviews"; }

    @Override
    public ServiceType getSeviceType() {
        return ServiceType.FEDERATION_SUBGRAPH;
    }

    @Override
    public Map<String, String> sdlFiles() { return ImmutableMap.of("schema.graphqls", schema); }

    @Override
    public CompletableFuture<Map<String, Object>> query(final ExecutionInput executionInput,
                                                        final GraphQLContext context) {
        return queryExecutor.query(executionInput, context);
    }

    public static String readFileAsString(String filePath) throws Exception {
        Path path = Paths.get(filePath);
        byte[] bytes = Files.readAllBytes(path);
        String content = new String(bytes, StandardCharsets.UTF_8);
        return content;
    }

I have implemented a simple webclientqueryexecutor as well as follows

package org.example;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.intuit.graphql.orchestrator.batch.QueryExecutor;
import graphql.ExecutionInput;
import graphql.GraphQLContext;
import org.springframework.core.ParameterizedTypeReference;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.web.reactive.function.BodyInserters;
import org.springframework.web.reactive.function.client.WebClient;
import reactor.core.publisher.Mono;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.CompletableFuture;

public class WebClientQueryExecutor implements QueryExecutor {
    private final WebClient webClient;
    private final String endpoint;
    public WebClientQueryExecutor(WebClient webClient, String endpoint) {
        this.webClient = webClient;
        this.endpoint = endpoint;
    }
    @Override
    public CompletableFuture<Map<String, Object>> query(ExecutionInput executionInput, GraphQLContext context) {
        System.out.println("/////////////////////////////////////////////////////////////");
        System.out.println(executionInput.getQuery());
        System.out.println(executionInput.getVariables());
        return executeQuery(executionInput)
                .toFuture();
    }
    private Mono<Map<String, Object>> executeQuery(final ExecutionInput executionInput) {
        System.out.println("-----------------------------------------------");
        System.out.println(executionInput.getQuery());
        System.out.println(endpoint);
        System.out.println(HttpHeaders.CONTENT_TYPE);
        System.out.println(MediaType.APPLICATION_JSON_VALUE);

        return webClient.post()
                .uri(endpoint)
                .body(BodyInserters.fromValue("{\"query\": \"" + executionInput.getQuery() + "\"}"))
                .header(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE)
                .retrieve()
                .bodyToMono(new ParameterizedTypeReference<Map<String, Object>>() {})
                .doOnSuccess(response -> {
                    // Print the response when it's successful
                    System.out.println("Response: " + response);
                })
                .doOnError(error -> {
                    // Print the error if there's an error
                    System.err.println("Error occurred: " + error.getMessage());
                });
    }
}

In my implementation then i stitched the two services and called a query as follows

public class Test4 {


    private static final WebClient webClient = create();
    private ExecutionInput executionInput;
    private static Map<String, Object> executionResult;

    public static void main(String[] args) throws Exception {

        ExecutionStrategy queryExecutionStrategy = new AsyncExecutionStrategy();
        Map<String, Object> executionResult;

        ShowsService showsService = new ShowsService("http://localhost:8080/graphql", webClient);
        ReviewsService reviewsService = new ReviewsService("http://localhost:8081/graphql", webClient);

        // create a runtimeGraph by stitching service providers
        RuntimeGraph runtimeGraph = SchemaStitcher.newBuilder()
                .service(showsService)
                .service(reviewsService)
                .build()
                .stitchGraph();

        GraphQLOrchestrator.Builder builder = GraphQLOrchestrator.newOrchestrator();
        builder.runtimeGraph(runtimeGraph);
        GraphQLOrchestrator graphQLOrchestrator = builder.build();

        String printSchema = new SchemaPrinter().print(runtimeGraph.getExecutableSchema());
        System.out.println(printSchema);

        ExecutionInput.Builder eiBuilder = ExecutionInput.newExecutionInput();
        eiBuilder.query(" query { shows{title reviews {starRating}}}");
        ExecutionInput executionInput = eiBuilder.build();

        executionResult = graphQLOrchestrator.execute(executionInput).get().toSpecification();

        System.out.println(executionResult);
    }
}

the query gets executed in the first level properly fetching the required typename and key from the parentType

Response: {data={getPersons=[{lastName=Stark, firstName=Tony}, {lastName=Wayne, firstName=Bruce}, {lastName=Parker, firstName=Peter}]}}

but when requesting the second graphs data by using the typeName and entities it throws the following error

query ($REPRESENTATIONS:[_Any!]!) {_entities(representations:$REPRESENTATIONS) {... on Person {address {state __typename}}}}
{REPRESENTATIONS=[{firstName=Tony, __typename=Person}, {firstName=Bruce, __typename=Person}, {firstName=Peter, __typename=Person}]}

Response: {errors=[{message=Variable 'REPRESENTATIONS' has an invalid value: Variable 'REPRESENTATIONS' has coerced Null value for NonNull type '[_Any!]!', locations=[{line=1, column=8}], extensions={classification=ValidationError}}]}

Can you please let me know if there is a workaround to this , a will attach a link that i found regarding this issue in dgs as well for your reference Netflix/dgs-framework#1058

thankyou