jarv.is/lib/migrations/hits-db.js

// Initialize a new pageview database. For use with Fauna Schema Migrate:
// https://github.com/fauna-labs/fauna-schema-migrate#readme

import faunadb from "faunadb";
const {
  CreateCollection,
  CreateIndex,
  CreateFunction,
  Query,
  Collection,
  Role,
  Var,
  Index,
  Let,
  Match,
  Lambda,
  Get,
  Create,
  Update,
  Add,
  Select,
  If,
  Exists,
  ToInteger,
} = faunadb.query;

export default function run() {
  // initializes the empty database
  CreateCollection({ name: "hits" });

  // this allows us to quickly pull a post's corresponding row
  CreateIndex({
    name: "hits_by_slug",
    source: Collection("hits"),
    terms: [
      {
        field: ["data", "slug"],
      },
    ],
    unique: false,
    serialized: true,
  });

  // a wrapper to get a post's row, add one to it, and return the new tally
  CreateFunction({
    name: "increment_hit",
    body: Query(
      Lambda(
        "slug",
        Let(
          { match: Match(Index("hits_by_slug"), Var("slug")) },
          If(
            Exists(Var("match")),
            Let(
              {
                ref: Select("ref", Get(Var("match"))),
                hits: ToInteger(Select("hits", Select("data", Get(Var("match"))))),
              },
              Update(Var("ref"), { data: { hits: Add(Var("hits"), 1) } })
            ),
            Create(Collection("hits"), { data: { slug: Var("slug"), hits: 1 } })
          )
        )
      )
    ),
    role: Role("server"),
  });
}