patrick91 / federation-merge

How to run this example

Install dependencies

in each frame folder run

pdm install

And also run

curl -sSL https://rover.apollo.dev/nix/latest | sh

To install rover

Run the services

in each frame folder run

pdm dev

Run Apollo Router in dev mode

in the root folder run

rover dev --supergraph-config supergraph.yaml

Then you should be able to access the Apollo Studio Explorer at http://localhost:4000

Queries:

standard federation query, field with the same name will only be fetched once usually from the first service

query Basic($id: ID!) {
  frame(id: $id) {
    id

    # unique fields will come from the correct service
    # (because they only live in that specific service)
    # for example:
    frameFord {
      id
      dataOnlyInFrameB
    }

    frameGpl {
      id
      dataOnlyInFrameA
    }
  }
}

similar to the one we had previously, but also with a common field, the common field will be resolved by only one subgraph

query CommonField($id: ID!) {
  frameWithAdditionalData(id: $id) {
    id
    commonField
    # try commenting one of these two fields
    # and see the value of common field update
    # Apollo Router tries to do the most efficient
    # query plan, in order to reduce the number of
    # data fetches
    dataOnlyInFrameA
    dataOnlyInFrameB
  }
}

in this approach we abuse some feature of federation in order to fetch the data from the correct subgraph in the frame field for the FrameWithRequires type we require the available_X field (using the @require directive) for every subgraph, so that we have a way of knowing if this frame is available in any of the frames subgraphs the annoying part of this is that we need to implement this field in all the subgraphs, and we also need some logic in our main Frame service to return the right type we also use an interface to make common fields easier to fetch

query FrameWithRequires($id: ID!) {
  frameWithRequires(id: $id) {
    id
    frame {
      id
      name

      ... on FrameA {
        dataOnlyInFrameA
      }

      ... on FrameB {
        dataOnlyInFrameB
      }
    }
  }
}

similar to the one before, but we assume the main Frame service has a way to know where the data comes from, in this case we only do a simple check on the id if the id is one then we return data from Frame A otherwise Frame B we can also add interfaces like above to make it easier to fetch

query FrameWithUnion($id: ID!) {
  frameWithUnion(id: $id) {
    ... on FrameA {
      dataOnlyInFrameA
      id
      name
    }
    ... on FrameB {
      dataOnlyInFrameB
      id
      name
    }
  }
}

this uses service to service communication to fetch the data from other subgraphs I've done a JSON field for time sake, but you can return any object too

query Http($id: ID!) {
  frameViaHttp(id: $id)
}