In this tutorial, you learn how to store and retrieve data in your Cloudflare Workers applications by building a REST API that manages an inventory catalog using [Fauna](https://fauna.com/) as its data layer.

## Learning goals

* How to store and retrieve data from Fauna in Workers.
* How to use Wrangler to store secrets securely.
* How to use [Hono](https://hono.dev) as a web framework for your Workers.

Building with Fauna, Workers, and Hono enables you to create a globally distributed, strongly consistent, fully serverless REST API in a single repository.

Fauna is a document-based database with a flexible schema. This allows you to define the structure of your data – whatever it may be – and store documents that adhere to that structure. In this tutorial, you will build a product inventory, where each `product` document must contain the following properties:

* **title** - A human-friendly string that represents the title or name of a product.
* **serialNumber** - A machine-friendly string that uniquely identifies the product.
* **weightLbs** - A floating point number that represents the weight in pounds of the product.
* **quantity** - A non-negative integer that represents how many items of a particular product there are in the inventory.

Documents are stored in a [collection](https://docs.fauna.com/fauna/current/reference/schema_entities/collection/). Collections in document databases are groups of related documents.

For this tutorial, all API endpoints are public. However, Fauna also offers multiple avenues for securing endpoints and collections. Refer to [Choosing an authentication strategy with Fauna](https://fauna.com/blog/choosing-an-authentication-strategy-with-fauna) for more information on authenticating users to your applications with Fauna.

## Before you start

All of the tutorials assume you have already completed the [Get started guide](https://developers.cloudflare.com/workers/get-started/guide/), which gets you set up with a Cloudflare Workers account, [C3](https://github.com/cloudflare/workers-sdk/tree/main/packages/create-cloudflare), and [Wrangler](https://developers.cloudflare.com/workers/wrangler/install-and-update/).

## Set up Fauna

### Create your database

To create a database, log in to the [Fauna Dashboard](https://dashboard.fauna.com/) and click **Create Database**. When prompted, select your preferred [Fauna region group](https://docs.fauna.com/fauna/current/manage/region-groups/) and other database settings.

Fauna Account

If you do not have a Fauna account, [sign up](https://dashboard.fauna.com/register) and deploy this template using the free tier.

### Create a collection

Create a `Products` collection for the database with the following query. To run the query in the Fauna Dashboard, select your database and click the **Shell** tab:

```js
Collection.create({ name: "Products" });
```

The query outputs a result similar to the following:

```js
{
  name: "Products",
  coll: Collection,
  ts: Time("2099-08-28T15:03:53.773Z"),
  history_days: 0,
  indexes: {},
  constraints: []
}
```

### Create a secret key

In production, the Worker will use the Cloudflare Fauna integration to automatically connect to Fauna. The integration creates any credentials needed for authentication with Fauna.

For local development, you must manually create a [Fauna authentication key](https://docs.fauna.com/fauna/current/learn/security/keys/) and pass the key's secret to your Worker as a [development secret](#add-your-fauna-database-key-for-local-development).

To create a Fauna authentication key:

1. In the upper left pane of Fauna Dashboard’s Explorer page, select your database, and click the **Keys** tab.

2. Click **Create Key**.

3. Choose a **Role** of **Server**.

4. Click **Save**.

5. Copy the **Key Secret**. The secret is scoped to the database.

Protect your keys

Server keys can read and write all documents in all collections and can call all [user-defined functions](https://docs.fauna.com/fauna/current/cookbook/data_model/user_defined_functions) (UDFs). Protect server keys and do not commit them to source control repositories.

## Manage your inventory with Workers

### Create a new Worker project

Create a new project by using [C3](https://github.com/cloudflare/workers-sdk/tree/main/packages/create-cloudflare).

* npm

  ```sh
  npm create cloudflare@latest -- fauna-workers
  ```

* pnpm

  ```sh
  pnpm create cloudflare@latest fauna-workers
  ```

* yarn

  ```sh
  yarn create cloudflare fauna-workers
  ```

To continue with this guide:

* For *What would you like to start with*?, select `Framework Starter`.
* For *Which development framework do you want to use?*, select `Hono`.
* For, *Do you want to deploy your application?*, select `No`.

Then, move into your newly created directory:

```sh
cd fauna-workers
```

Update the Wrangler file to set the name for the Worker.

* wrangler.jsonc

  ```jsonc
  {
    "name": "fauna-workers"
  }
  ```

* wrangler.toml

  ```toml
  name = "fauna-workers"
  ```

### Add your Fauna database key for local development

For local development, add a `.dev.vars` file on the project root and add your Fauna key's secret as a [development secret](https://developers.cloudflare.com/workers/configuration/secrets/#local-development-with-secrets):

```plain
DATABASE_KEY=<FAUNA_SECRET>
```

### Add the Fauna integration

Deploy your Worker to Cloudflare to ensure that everything is set up correctly:

```sh
npm run deploy
```

1. Login to your [Cloudflare dashboard](https://dash.cloudflare.com/).

2. Select the **Integrations** tab and click on the **Fauna** integration.

   ![Selecting the fauna integration](https://developers.cloudflare.com/_astro/integrate_fauna.BXZ8FjPS_Z20005z.webp)

3. Login to your Fauna account.

4. Select the Fauna database you created earlier.

5. Select `server` role as your database role.

6. Enter `DATABASE_KEY` as the **Secret Name**.

7. Select **Finish**.

8. Navigate to **Settings** tab and select **Variables**. Notice that a new variable `DATABASE_KEY` is added to your Worker.

The integration creates a new Fauna authentication key and stores the key's secret in the Worker's `DATABASE_KEY` secret. The deployed Worker uses this key.

Note

You can manage the generated Fauna key in the Fauna Dashboard. See the [Clouflare Fauna integration docs](https://developers.cloudflare.com/workers/databases/native-integrations/fauna).

### Install dependencies

Install [the Fauna JavaScript driver](https://github.com/fauna/fauna-js) in your newly created Worker project.

* npm

  ```sh
  npm install fauna
  ```

* yarn

  ```sh
  yarn add fauna
  ```

### Base inventory logic

Replace the contents of your `src/index.ts` file with the skeleton of your API:

```ts
import { Hono } from "hono";
import { Client, fql, ServiceError } from "fauna";


type Bindings = {
  DATABASE_KEY: string;
};


type Variables = {
  faunaClient: Client;
};


type Product = {
  id: string;
  serialNumber: number;
  title: string;
  weightLbs: number;
  quantity: number;
};


const app = new Hono<{ Bindings: Bindings; Variables: Variables }>();


app.use("*", async (c, next) => {
  const faunaClient = new Client({
    secret: c.env.DATABASE_KEY,
  });
  c.set("faunaClient", faunaClient);
  await next();
});


app.get("/", (c) => {
  return c.text("Hello World");
});


export default app;
```

This is custom middleware to initialize the Fauna client and set the instance with `c.set()` for later use in another handler:

```js
app.use("*", async (c, next) => {
  const faunaClient = new Client({
    secret: c.env.DATABASE_KEY,
  });
  c.set("faunaClient", faunaClient);
  await next();
});
```

You can access the `DATABASE_KEY` environment variable from `c.env.DATABASE_KEY`. Workers run on a [custom JavaScript runtime](https://developers.cloudflare.com/workers/runtime-apis/) instead of Node.js, so you cannot use `process.env` to access your environment variables.

### Create product documents

Add your first Hono handler to the `src/index.ts` file. This route accepts `POST` requests to the `/products` endpoint:

```ts
app.post("/products", async (c) => {
  const { serialNumber, title, weightLbs } =
    await c.req.json<Omit<Product, "id">>();
  const query = fql`Products.create({
    serialNumber: ${serialNumber},
    title: ${title},
    weightLbs: ${weightLbs},
    quantity: 0
  })`;
  const result = await c.var.faunaClient.query<Product>(query);
  return c.json(result.data);
});
```

Handler order

In Hono, you should place your handler below the custom middleware. This is because middleware and handlers are executed in sequence from top to bottom. If you place the handler first, you cannot retrieve the instance of the Fauna client using `c.var.faunaClient`.

This route applied an FQL query in the `fql` function that creates a new document in the **Products** collection:

```js
fql`Products.create({
  serialNumber: ${serialNumber},
  title: ${title},
  weightLbs: ${weightLbs},
  quantity: 0
})`;
```

To review what a document looks like, run the following query. In the Fauna dashboard, go to **Explorer** > Region name > Database name like a `cloudflare_rest_api` > the **SHELL** window:

```js
Products.create({
  serialNumber: "A48432348",
  title: "Gaming Console",
  weightLbs: 5,
  quantity: 0,
});
```

Fauna returns the created document:

```js
{
  id: "<document_id>",
  coll: Products,
  ts: "<timestamp>",
  serialNumber: "A48432348",
  title: "Gaming Console",
  weightLbs: 5,
  quantity: 0
}
```

Examining the route you create, when the query is successful, the data newly created document is returned in the response body:

```js
return c.json({
  productId: result.data,
});
```

### Error handling

If Fauna returns any error, an exception is raised by the client. You can catch this exception in `app.onError()`, then retrieve and respond with the result from the instance of `ServiceError`.

```ts
app.onError((e, c) => {
  if (e instanceof ServiceError) {
    return c.json(
      {
        status: e.httpStatus,
        code: e.code,
        message: e.message,
      },
      e.httpStatus,
    );
  }
  console.trace(e);
  return c.text("Internal Server Error", 500);
});
```

### Retrieve product documents

Next, create a route that reads a single document from the **Products** collection.

Add the following handler to your `src/index.ts` file. This route accepts `GET` requests at the `/products/:productId` endpoint:

```ts
app.get("/products/:productId", async (c) => {
  const productId = c.req.param("productId");
  const query = fql`Products.byId(${productId})`;
  const result = await c.var.faunaClient.query<Product>(query);
  return c.json(result.data);
});
```

The FQL query uses the [`byId()`](https://docs.fauna.com/fauna/current/reference/schema_entities/collection/instance-byid) method to retrieve a full document from the **Productions** collection:

```js
fql`Products.byId(productId)`;
```

If the document exists, return it in the response body:

```ts
return c.json(result.data);
```

If not, an error is returned.

### Delete product documents

The logic to delete product documents is similar to the logic for retrieving products. Add the following route to your `src/index.ts` file:

```ts
app.delete("/products/:productId", async (c) => {
  const productId = c.req.param("productId");
  const query = fql`Products.byId(${productId})!.delete()`;
  const result = await c.var.faunaClient.query<Product>(query);
  return c.json(result.data);
});
```

The only difference from the previous route is that you use the [`delete()`](https://docs.fauna.com/fauna/current/reference/auth/key/delete) method, combined with the `byId()` method, to delete a document.

When the delete operation is successful, Fauna returns the deleted document and the route forwards the deleted document in the response's body. If not, an error is returned.

## Test and deploy your Worker

Before deploying your Worker, test it locally by using Wrangler's [`dev`](https://developers.cloudflare.com/workers/wrangler/commands/#dev) command:

* npm

  ```sh
  npm run dev
  ```

* yarn

  ```sh
  yarn dev
  ```

Once the development server is up and running, start making HTTP requests to your Worker.

First, create a new product:

```sh
curl \
    --data '{"serialNumber": "H56N33834", "title": "Bluetooth Headphones", "weightLbs": 0.5}' \
    --header 'Content-Type: application/json' \
    --request POST \
    http://127.0.0.1:8787/products
```

You should receive a `200` response similar to the following:

```json
{
  "productId": "<document_id>"
}
```

Note

Copy the `productId` value for use in the remaining test queries.

Next, read the document you created:

```sh
curl \
    --header 'Content-Type: application/json' \
    --request GET \
    http://127.0.0.1:8787/products/<document_id>
```

The response should be the new document serialized to JSON:

```json
{
  "coll": {
    "name": "Products"
  },
  "id": "<document_id>",
  "ts": {
    "isoString": "<timestamp>"
  },
  "serialNumber": "H56N33834",
  "title": "Bluetooth Headphones",
  "weightLbs": 0.5,
  "quantity": 0
}
```

Finally, deploy your Worker using the [`wrangler deploy`](https://developers.cloudflare.com/workers/wrangler/commands/#deploy) command:

* npm

  ```sh
  npm run deploy
  ```

* yarn

  ```sh
  yarn deploy
  ```

This publishes the Worker to your `*.workers.dev` subdomain.

## Update inventory quantity

As the last step, implement a route to update the quantity of a product in your inventory, which is `0` by default.

This will present a problem. To calculate the total quantity of a product, you first need to determine how many items there currently are in your inventory. If you solve this in two queries, first reading the quantity and then updating it, the original data might change.

Add the following route to your `src/index.ts` file. This route responds to HTTP `PATCH` requests on the `/products/:productId/add-quantity` URL endpoint:

```ts
app.patch("/products/:productId/add-quantity", async (c) => {
  const productId = c.req.param("productId");
  const { quantity } = await c.req.json<Pick<Product, "quantity">>();
  const query = fql`Products.byId(${productId}){ quantity : .quantity + ${quantity}}`;
  const result =
    await c.var.faunaClient.query<Pick<Product, "quantity">>(query);
  return c.json(result.data);
});
```

Examine the FQL query in more detail:

```js
fql`Products.byId(${productId}){ quantity : .quantity + ${quantity}}`;
```

Consistency guarantees in Fauna

Even if multiple Workers update this quantity from different parts of the world, Fauna guarantees the consistency of the data across all Fauna regions. This article on [consistency](https://fauna.com/blog/consistency-without-clocks-faunadb-transaction-protocol?utm_source=Cloudflare\&utm_medium=referral\&utm_campaign=Q4_CF_2021) explains how Fauna's distributed protocol works without the need for atomic clocks.

Test your update route:

```sh
curl \
    --data '{"quantity": 5}' \
    --header 'Content-Type: application/json' \
    --request PATCH \
    http://127.0.0.1:8787/products/<document_id>/add-quantity
```

The response should be the entire updated document with five additional items in the quantity:

```json
{
  "quantity": 5
}
```

Update your Worker by deploying it to Cloudflare.

* npm

  ```sh
  npm run deploy
  ```

* yarn

  ```sh
  yarn deploy
  ```
