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Local GraphQL resolution

Next, explore local GraphQL resolution with the Bookinfo sample application.

In Gloo Gateway, you can create GraphQL resolvers to fetch the data from your backend when using local execution. Today Gloo Gateway supports local execution with REST and gRPC resolvers, and remote execution for GraphQL servers. In the following steps, you create resolvers that point to Bookinfo services and use the resolvers in a GraphQL schema.

Note that this example uses local execution, which means the Envoy server executes GraphQL queries locally before it proxies them to the Bookinfo upstreams that provide the data requested in the queries.

Deploy the Bookinfo sample application to the default namespace, which you will expose behind a GraphQL server embedded in Envoy.
```
kubectl apply -f https://raw.githubusercontent.com/istio/istio/master/samples/bookinfo/platform/kube/bookinfo.yaml
```
Verify that Gloo Gateway automatically discovered the Bookinfo services and created corresponding default-productpage-9080 upstream, which you will use in the REST resolver.
```
kubectl get upstream -n gloo-system
```

Check out the contents of the following Gloo Gateway GraphQL API CRD. Specifically, take a look at the restResolver and schemaDefinition sections.

curl https://raw.githubusercontent.com/solo-io/graphql-bookinfo/main/kubernetes/bookinfo-gql.yaml

restResolver: A resolver is defined by a name (ex: Query|productsForHome) and whether it is a REST or a gRPC resolver. This example is a REST resolver, so the path and the method that are needed to request the data are specified. The path can reference a parent attribute, such as /details/{$parent.id}.

resolutions:
  Query|productsForHome:
    restResolver:
      request:
        headers:
          :method: GET
          :path: /api/v1/products
      upstreamRef:
        name: default-productpage-9080
        namespace: gloo-system

schemaDefinition: A schema definition determines what kind of data can be returned to a client that makes a GraphQL query to your endpoint. The schema specifies the data that a particular type, or service, returns in response to a GraphQL query. In this example, fields are defined for the three Bookinfo services, Product, Review, and Rating. Additionally, the schema definition indicates which services reference the resolvers. In this example, the Product service references the Query|productForHome resolver.

schemaDefinition: |
  type Query {
    productsForHome: [Product] @resolve(name: "Query|productsForHome")
  }

  type Product {
    id: String
    title: String
    descriptionHtml: String
    author: String @resolve(name: "author")
    pages: Int @resolve(name: "pages")
    year: Int @resolve(name: "year")
    reviews : [Review] @resolve(name: "reviews")
    ratings : [Rating] @resolve(name: "ratings")
  }

  type Review {
    reviewer: String
    text: String
  }

  type Rating {
    reviewer : String
    numStars : Int
  }

Create the GraphQL API CRD in your cluster to expose the GraphQL API that fetches data from the three Bookinfo services.

kubectl apply -f https://raw.githubusercontent.com/solo-io/graphql-bookinfo/main/kubernetes/bookinfo-gql.yaml -n gloo-system

Update the default virtual service that you previously created to route traffic to /graphql to the new bookinfo-graphql GraphQL API.

cat << EOF | kubectl apply -f -
apiVersion: gateway.solo.io/v1
kind: VirtualService
metadata:
  name: 'default'
  namespace: 'gloo-system'
spec:
  virtualHost:
    domains:
    - '*'
    routes:
    - graphqlApiRef:
        name: bookinfo-graphql
        namespace: gloo-system
      matchers:
      - prefix: /graphql
EOF

Send a request to the GraphQL endpoint to verify that the request is successfully resolved by Envoy.

curl "$(glooctl proxy url)/graphql" -H 'Content-Type: application/json' -d '{"query": "query {productsForHome {id, title, author, pages, year}}"}'

In the JSON response, note that only the information you queried is returned:

{"data":{"productsForHome":[{"id":"0","title":"The Comedy of Errors","author":"William Shakespeare","pages":200,"year":1595}]}}

Up next: Explore remote GraphQL resolution with an example GraphQL server upstream.