Follow-along: Add the listings subgraph

1. Create a new file called listings.graphql and paste the following schema:

   listings.graphql

   extend schema
     @link(url: "https://specs.apollo.dev/federation/v2.11", import: ["@key"])
   
   type Query {
     "A curated array of listings to feature on the homepage"
     featuredListings: [Listing!]!
   
     # # EXERCISE: LISTING DETAILS
     # "A specific listing"
     # listing(id: ID!): Listing
   }
   
   "A particular intergalactic location available for booking"
   type Listing {
     id: ID!
     "The listing's title"
     title: String!
     "The number of beds available"
     numOfBeds: Int
     "The cost per night"
     costPerNight: Float
     "Indicates whether listing is closed for bookings (on hiatus)"
     closed: Boolean
     # # EXERCISE: LISTING ACTIVITIES
     # "The activities available for this listing"
     # activities: [Activity!]!
   }
   
   # # EXERCISE: LISTING ACTIVITIES
   # type Activity {
   #   id: ID!
   #   name: String!
   #   description: String
   #   terrain: String
   #   groupSize: Int
   # }

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2. Open up the supergraph.yaml file.

3. Update the configuration to include the listings subgraph under the subgraphs property. (It should be at the same level as products).

   supergraph.yaml

   subgraphs:
     products:
       routing_url: http://ignored
       schema:
         file: products.graphql
     listings:
       routing_url: http://ignored # this value is ignored
       schema:
         file: listings.graphql
   federation_version: =2.11.0

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4. Save your changes and rover dev will restart, composing the listings subgraph schema.

5. Go to http://localhost:4000. We'll add the new entry point to our operation for featuredListings.

   GraphQL operation

   query GetProductsAndListings {
     products {
       id
       name
       description
       category
     }
     featuredListings {
       id
       title
     }
   }

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6. We'll get an error because our listings subgraph is not set up to return anything yet!

   Response errors

   {
     "data": null,
     "errors": [
       {
         "message": "HTTP fetch failed from 'listings': HTTP fetch failed from 'listings': error trying to connect: dns error: no record found for Query { name: Name(\"ignored.\"), query_type: AAAA, query_class: IN }",
         "path": [],
         "extensions": {
           "code": "SUBREQUEST_HTTP_ERROR",
           "service": "listings",
           "reason": "HTTP fetch failed from 'listings': error trying to connect: dns error: no record found for Query { name: Name(\"ignored.\"), query_type: AAAA, query_class: IN }"
         }
       }
     ],
     "extensions": {
       "valueCompletion": [
         {
           "message": "Cannot return null for non-nullable field Query.featuredListings",
           "path": []
         }
       ]
     }
   }

In the next exercise, you'll fix those errors!