Running

cd into each subgraph directory and npm install npm start.

Once each subgraph is running cd into the gateway directory and npm install npm start.

Testing

Make the following request to http://localhost:5000/graphql

query TestOldQuery {
    oldQuery {
        id
        oldField
        author { 
            id
            name
         }
    }
}

Expected behavior

Since all required fields in the query can be resolved by the old-book-subgraph and the author-subgraph we should see the query plan only include those two subgraphs.

Actual behavior

The query plan includes the new-book-subgraph which is not required to resolve the query. It fetches the authorId from the new-book-subgraph even though it could be resolved by the old-book-subgraph.

QueryPlan {
  Sequence {
    Fetch(service: "old-book-subgraph") {
      {
        oldQuery {
          __typename
          id
          oldField
        }
      }
    },
    Flatten(path: "oldQuery") {
      Fetch(service: "new-book-subgraph") {
        {
          ... on Book {
            __typename
            id
          }
        } =>
        {
          ... on Book {
            authorId
          }
        }
      },
    },
    Flatten(path: "oldQuery") {
      Fetch(service: "author-subgraph") {
        {
          ... on Book {
            __typename
            authorId
            id
          }
        } =>
        {
          ... on Book {
            author {
              id
              name
            }
          }
        }
      },
    },
  },
}

Note: If newQuery is used as the entrypoint instead then the query plan only includes the new-book-subgraph and author-subgraph as expected.

query TestNewQuery {
    newQuery {
        id
        newField
        author { 
            id
            name
         }
    }
}

@provides

This same issue exists even if we explicitly define @provides on the oldQuery.

To test this run old-book-subgraph-provides and update gateway/index.js according to the TODO.

Run the same TestOldQuery as above and see the same query plan that includes new-book-subgraph even though the old-book-subgraph-provides explicitly @provides authorId on the query path.