N+1 in union types

Setup

prerequisites

install router binary in current directory, or symlink or copy existing

ruby >= 3.0 is required for this to work, but samples can be replicated in other language

# install gems
bundle install
# install foreman
gem install foremal
# start all processes
foreman start

Commands used to run and generate files

file	command	description
schemaa_federation_sdl.graphql	bundle exec ruby ./schema_a.rb -f	Schema of the subgraph A
schemab_federation_sdl.graphql	bundle exec ruby ./schema_b.rb -f	Schema of the subgraph B
supergraph.graphql	rover supergraph compose --config ./supergraph-config.yml > supergraph.graphql	supergraph schema

List of processes in Procfile

name	command	desc
router	./router --dev --supergraph supergraph.graphql --log info -c config.yml	router binary
schemaA	bundle exec ruby ./schema_a.rb	subgraph A
schemaA	bundle exec ruby ./schema_b.rb	subgraph B

query used

query ExampleQuery {
  actions {
    config {
      ... on ConfigOne {
        id
        otherTemplate {
          name
          body
          id
        }
        someTemplate {
          name
          body
          id
        }
      }
      ... on ConfigThree {
        id
        wrongTemplate {
          name
          body
          id
        }
      }
      ... on ConfigTwo {
        id
        leftTemplate {
          name
          body
          id
        }
        rightTemplate {
          name
          body
          id
        }
      }
    }
  }
}

QueryPlan {
  Sequence {
    Fetch(service: "schemaA") {
      {
        actions {
          config {
            __typename
            ... on ConfigOne {
              id
              otherTemplate {
                __typename
                id
              }
              someTemplate {
                __typename
                id
              }
            }
            ... on ConfigThree {
              id
              wrongTemplate {
                __typename
                id
              }
            }
            ... on ConfigTwo {
              id
              leftTemplate {
                __typename
                id
              }
              rightTemplate {
                __typename
                id
              }
            }
          }
        }
      }
    },
    Parallel {
      Flatten(path: "[email protected]") {
        Fetch(service: "schemaB") {
          {
            ... on Template {
              __typename
              id
            }
          } =>
          {
            ... on Template {
              name
              body
            }
          }
        },
      },
      Flatten(path: "[email protected]") {
        Fetch(service: "schemaB") {
          {
            ... on Template {
              __typename
              id
            }
          } =>
          {
            ... on Template {
              name
              body
            }
          }
        },
      },
      Flatten(path: "[email protected]") {
        Fetch(service: "schemaB") {
          {
            ... on Template {
              __typename
              id
            }
          } =>
          {
            ... on Template {
              name
              body
            }
          }
        },
      },
      Flatten(path: "[email protected]") {
        Fetch(service: "schemaB") {
          {
            ... on Template {
              __typename
              id
            }
          } =>
          {
            ... on Template {
              name
              body
            }
          }
        },
      },
      Flatten(path: "[email protected]") {
        Fetch(service: "schemaB") {
          {
            ... on Template {
              __typename
              id
            }
          } =>
          {
            ... on Template {
              name
              body
            }
          }
        },
      },
    },
  },
}