Increment a counter using Fauna and GraphQL

README.md

Increment a counter using Fauna and GraphQL

Step by step instructions to implement this solution by Luigi Servini in the Fauna forums.

1. Save schema.graphql from this gist on your machine.
2. Create a new database in the Fauna dashboard.
3. On the GraphQL tab, choose Import Schema then upload schema.graphql.
4. On the Collections tab, select the Counter collection and choose New Document to create a new document. Copy and paste the contents of counter.json then choose Save.
5. Copy the ID of the new document, e.g., 294683317926625795.
6. On the Functions tab, select the user-defined function (UDF) increment_counter. Copy the code from increment_counter.fql and paste it into Function Body. Replace <document_id> with the document ID you copied in the previous step and choose Save.
7. Return to the GraphQL tab, copy the GraphQL query from query.graphql, and paste the query in the GraphQL playground. When you run your query you should receive:

{
  "data": {
    "nextCounter": {
      "counter": 1
    }
  }
}

Counter.json

{
  "counter": 0
}

increment_counter.fql

Query(
  Lambda(
    [],
    Let(
      {
        counter: Get(Ref(Collection("Counter"), "<document_id>")),
        counterRef: Select(["ref"], Var("counter")),
        counterValue: Select(["data", "counter"], Var("counter"))
      },
      Update(Var("counterRef"), {
        data: { counter: Add(Var("counterValue"), 1) }
      })
    )
  )
)

query.graphql

{
  nextCounter {
    counter
  }
}

schema.graphql

type Counter {
  counter: Int!
} 

type Query {
  nextCounter: Counter! @resolver(name: "increment_counter")
}