How access Fauna's "after" cursors in Next.js API routes

[ryansumma]

I am building an application using Next.Js and Fauna where when a user visits the /accounts route, it fetches Next.js API route /api/fauna/accounts which makes a query to Fauna to get all the accounts the user owns then returns that response to the page and renders the data in a table.

Fetch inside /accounts looks like so:

function Accounts() {
  const [data, setData] = useState(null)

  useEffect(() => {
    fetch('api/accounts')
      .then((res) => res.json())
      .then((data) => {
        setData(data)
      })
  }, [])


  return (
    <Table>
      {...data}
    </Table>
  )
}

The response inside /api/fauna/accounts returns an “after” cursor used for pagination. This is what the response looks like on the server inside /api/fauna/accounts

{
  after: [
    Time("2022-03-08T15:59:43.284410Z"),
    Ref(Collection("accounts"), "325579003214692417"),
    Ref(Collection("accounts"), "325579003214692417")
  ],
  data: [...]
}

However, when that response is sent back to the /accounts route, the “after” cursor is formatted completely differently than on the server which makes it difficult to paginate with. The response for the “after” cursor looks like this:

{
  after: [
    { "@ts": "2022-03-08T15:49:23.686204Z" },
    {
      "@ref": {
        id: "325578353522245700",
        collection: { "@ref": { id: "accounts", collection: { "@ref": { id: "collections" } } } }
      }
    },
    {
      "@ref": {
        id: "325578353522245700",
        collection: { "@ref": { id: "accounts", collection: { "@ref": { id: "collections" } } } }
      }
    }
  ],
  data: [...]
}

How do I paginate to the next page when the “after” cursor is formated like so?

[ewan]

The format that you’re seeing is Fauna’s wire protocol. JSON doesn’t handle embedded objects like References (among other complex response values), so those get serialized in a way that can be round-tripped.

The JavaScript driver includes a utility library called _json.js, which can take care of reconstituting the original cursor value:

const faunadb = require('faunadb')
const json = require('faunadb/src/_json')
const q = faunadb.query

// assuming response contains the wire protocol data from a pagination query
const deserialized = json.parseJSON(response)

// then you can include the `after` field in a subsequent query
const response2 = client.query(
  q.Paginate(
    q.Match(q.Index("your_index"), [<terms>]),
    {
      after: deserialized.after
    }
  )
)
.then(res => console.log(res))
.catch(err => console.err("Error:", err))