---
title: "Database"
description: "Choosing the right database configuration"
icon: Database
tags: ["documentation"]
---

In order to use **bknd**, you need to prepare access information to your database and potentially install additional dependencies. Connections to the database are managed using Kysely. Therefore, all [its dialects](https://kysely.dev/docs/dialects) are theoretically supported.

Currently supported and tested databases are:

- SQLite (embedded): Node.js SQLite, Bun SQLite, LibSQL, SQLocal
- SQLite (remote): Turso, Cloudflare D1
- Postgres: Vanilla Postgres, Supabase, Neon, Xata

By default, bknd will try to use a SQLite database in-memory. Depending on your runtime, a different SQLite implementation will be used.

## Defining the connection

There are mainly 3 ways to define the connection to your database, when

1. creating an app using `App.create()` or `createApp()`
2. creating an app using a [Framework or Runtime adapter](/integration/introduction)
3. starting a quick instance using the [CLI](/usage/cli#using-configuration-file-bknd-config)

When creating an app using `App.create()` or `createApp()`, you can pass a connection object in the configuration object.

```typescript title="app.ts"
import { createApp } from "bknd";
import { sqlite } from "bknd/adapter/sqlite";

// a connection is required when creating an app like this
const app = createApp({
  connection: sqlite({ url: ":memory:" }),
});
```

When using an adapter, or using the CLI, bknd will automatically try to use a SQLite implementation depending on the runtime:

```javascript title="app.js"
import { serve } from "bknd/adapter/node";

serve({
  // connection is optional, but recommended
  connection: { url: "file:data.db" },
});
```

You can also pass a connection instance to the `connection` property to explictly use a specific connection.

```javascript title="app.js"
import { serve } from "bknd/adapter/node";
import { sqlite } from "bknd/adapter/sqlite";

serve({
  connection: sqlite({ url: "file:data.db" }),
});
```

If you're using [`bknd.config.*`](/extending/config), you can specify the connection on the exported object.

```typescript title="bknd.config.ts"
import type { BkndConfig } from "bknd";

export default {
  connection: { url: "file:data.db" },
} satisfies BkndConfig;
```

Throughout the documentation, it is assumed you use `bknd.config.ts` to define your connection.

## SQLite

### Using config object

<Callout type="warn">
  When run with Node.js, a version of 22 (LTS) or higher is required. Please
  verify your version by running `node -v`, and
  [upgrade](https://nodejs.org/en/download/) if necessary.
</Callout>

The `sqlite` adapter is automatically resolved based on the runtime.

| Runtime                        | Adapter       | In-Memory | File | Remote |
| ------------------------------ | ------------- | --------- | ---- | ------ |
| Node.js                        | `node:sqlite` | ✅        | ✅   | ❌     |
| Bun                            | `bun:sqlite`  | ✅        | ✅   | ❌     |
| Cloudflare Worker/Browser/Edge | `libsql`      | 🟠        | 🟠   | ✅     |

The bundled version of the `libsql` connection only works with remote databases. However, you can pass in a `Client` from `@libsql/client`, see [LibSQL](#libsql) for more details.

```typescript title="bknd.config.ts"
import type { BkndConfig } from "bknd";

// no connection is required, bknd will use a SQLite database in-memory
// this does not work on edge environments!
export default {} satisfies BkndConfig;

// or explicitly in-memory
export default {
  connection: { url: ":memory:" },
} satisfies BkndConfig;

// or explicitly as a file
export default {
  connection: { url: "file:<path/to/your/database.db>" },
} satisfies BkndConfig;
```

### Node.js SQLite

To use the Node.js SQLite adapter directly, use the `nodeSqlite` function as value for the `connection` property. This lets you customize the database connection, such as enabling WAL mode.

```typescript title="bknd.config.ts"
import { nodeSqlite, type NodeBkndConfig } from "bknd/adapter/node";

export default {
  connection: nodeSqlite({
    url: "file:<path/to/your/database.db>",
    onCreateConnection: (db) => {
      db.exec("PRAGMA journal_mode = WAL;");
    },
  }),
} satisfies NodeBkndConfig;
```

### Bun SQLite

You can explicitly use the Bun SQLite adapter by passing the `bunSqlite` function to the `connection` property. This allows further configuration of the database, e.g. enabling WAL mode.

```typescript title="bknd.config.ts"
import { bunSqlite, type BunBkndConfig } from "bknd/adapter/bun";

export default {
  connection: bunSqlite({ 
    url: "file:<path/to/your/database.db>",
    onCreateConnection: (db) => {
      db.run("PRAGMA journal_mode = WAL;");
    },
  }),
} satisfies BunBkndConfig;
```

### LibSQL

Turso offers a SQLite-fork called LibSQL that runs a server around your SQLite database. The edge-version of the adapter is included in the bundle (remote only):

```typescript title="bknd.config.ts"
import { libsql, type BkndConfig } from "bknd";

export default {
  connection: libsql({
    url: "libsql://<database>.turso.io",
    authToken: "<auth-token>",
  }),
} satisfies BkndConfig;
```

If you wish to use LibSQL as file, in-memory or make use of [Embedded Replicas](https://docs.turso.tech/features/embedded-replicas/introduction), you have to pass in the `Client` from `@libsql/client`:

```typescript title="bknd.config.ts"
import { libsql, type BkndConfig } from "bknd";
import { createClient } from "@libsql/client";

const client = createClient({
  url: "libsql://<database>.turso.io",
  authToken: "<auth-token>",
});

export default {
  connection: libsql(client),
} satisfies BkndConfig;
```

### Cloudflare D1

Using the [Cloudflare Adapter](/integration/cloudflare), you can choose to use a D1 database binding. To do so, you only need to add a D1 database to your `wrangler.toml` and it'll pick up automatically.

To manually specify which D1 database to take, you can specify it explicitly:

```ts
import { serve, d1 } from "bknd/adapter/cloudflare";

export default serve<Env>({
  app: (env) => d1({ binding: env.D1_BINDING }),
});
```

### SQLocal

To use bknd with `sqlocal` for a offline expierence, you need to install the `@bknd/sqlocal` package. You can do so by running the following command:

```bash
npm install @bknd/sqlocal
```

This package uses `sqlocal` under the hood. Consult the [sqlocal documentation](https://sqlocal.dallashoffman.com/guide/setup) for connection options:

```js
import { createApp } from "bknd";
import { SQLocalConnection } from "@bknd/sqlocal";

const app = createApp({
  connection: new SQLocalConnection({
    databasePath: ":localStorage:",
    verbose: true,
  }),
});
```

## PostgreSQL

To use bknd with Postgres, you need to install the `@bknd/postgres` package. You can do so by running the following command:

```bash
npm install @bknd/postgres
```

You can connect to your Postgres database using `pg` or `postgres` dialects. Additionally, you may also define your custom connection.

### Using `pg`

To establish a connection to your database, you can use any connection options available on the [`pg`](https://node-postgres.com/apis/client) package.

```js
import { serve } from "bknd/adapter/node";
import { pg } from "@bknd/postgres";

/** @type {import("bknd/adapter/node").NodeBkndConfig} */
const config = {
  connection: pg({
    connectionString: "postgresql://user:password@localhost:5432/database",
  }),
};

serve(config);
```

### Using `postgres`

To establish a connection to your database, you can use any connection options available on the [`postgres`](https://github.com/porsager/postgres) package.

```js
import { serve } from "bknd/adapter/node";
import { postgresJs } from "@bknd/postgres";

serve({
  connection: postgresJs("postgresql://user:password@localhost:5432/database"),
});
```

### Using custom connection

Several Postgres hosting providers offer their own clients to connect to their database, e.g. suitable for serverless environments.

Example using `@neondatabase/serverless`:

```js
import { createCustomPostgresConnection } from "@bknd/postgres";
import { NeonDialect } from "kysely-neon";

const neon = createCustomPostgresConnection("neon", NeonDialect);

serve({
  connection: neon({
    connectionString: process.env.NEON,
  }),
});
```

Example using `@xata.io/client`:

```js
import { createCustomPostgresConnection } from "@bknd/postgres";
import { XataDialect } from "@xata.io/kysely";
import { buildClient } from "@xata.io/client";

const client = buildClient();
const xata = new client({
  databaseURL: process.env.XATA_URL,
  apiKey: process.env.XATA_API_KEY,
  branch: process.env.XATA_BRANCH,
});

const xataConnection = createCustomPostgresConnection("xata", XataDialect, {
  supports: {
    batching: false,
  },
});

serve({
  connection: xataConnection({ xata }),
});
```

## Custom Connection

Creating a custom connection is as easy as extending the `Connection` class and passing constructing a Kysely instance.

```ts
import { createApp, Connection } from "bknd";
import { Kysely } from "kysely";

class CustomConnection extends Connection {
  constructor() {
    const kysely = new Kysely(/* ... */);
    super(kysely);
  }
}

const connection = new CustomConnection();

// e.g. and then, create an instance
const app = createApp({ connection });
```

## Data Structure

To provide a database structure, you can pass `config` to the creation of an app. In [`db` mode](/usage/introduction#ui-only-mode), the data structure is only respected if the database is empty. If you made updates, ensure to delete the database first, or perform updates through the Admin UI.
  
Here is a quick example:

```typescript
import { createApp, em, entity, text, number } from "bknd";

const schema = em(
  {
    posts: entity("posts", {
      // "id" is automatically added
      title: text().required(),
      slug: text().required(),
      content: text(),
      views: number(),
    }),
    comments: entity("comments", {
      content: text(),
    }),

    // relations and indices are defined separately.
    // the first argument are the helper functions, the second the entities.
  },
  ({ relation, index }, { posts, comments }) => {
    relation(comments).manyToOne(posts);
    // relation as well as index can be chained!
    index(posts).on(["title"]).on(["slug"], true);
  },
);

// to get a type from your schema, use:
type Database = (typeof schema)["DB"];
// type Database = {
//    posts: {
//       id: number;
//       title: string;
//       content: string;
//       views: number;
//    },
//    comments: {
//       id: number;
//       content: string;
//    }
// }

// pass the schema to the app
const app = createApp({
  config: {
    data: schema.toJSON(),
  },
});
```

Note that we didn't add relational fields directly to the entity, but instead defined them afterwards. That is because the relations are managed outside the entity scope to have an unified expierence for all kinds of relations (e.g. many-to-many).

<Callout type="info">
  Defined relations are currently not part of the produced types for the
  structure. We're working on that, but in the meantime, you can define them
  manually.
</Callout>

### System entities

There are multiple system entities which are added depending on if the module is enabled:
- `users`: if authentication is enabled
- `media`: if media is enabled and an adapter is configured

You can add additional fields to these entities. System-defined fields don't have to be repeated, those are automatically added to the entity, so don't worry about that. It's important though to match the system entities name, otherwise a new unrelated entity will be created.

If you'd like to connect your entities to system entities, you need them in the schema to access their reference when making relations. From the example above, if you'd like to connect the `posts` entity to the `users` entity, you can do so like this:

```typescript
import { em, entity, text, number, systemEntity } from "bknd";

const schema = em(
  {
    posts: entity("posts", {
      title: text().required(),
      slug: text().required(),
      content: text(),
      views: number(),
      // don't add the foreign key field, it's automatically added
    }),
    comments: entity("comments", {
      content: text(),
    }),
    // [!code highlight]
    // add a `users` entity 
    users: systemEntity("users", { // [!code highlight]
      // [!code highlight]
      // optionally add additional fields
    }) // [!code highlight]
  },
  // now you have access to the system entity "users"
  ({ relation, index }, { posts, comments, users }) => {
    // ... other relations
    relation(posts).manyToOne(users); // [!code highlight]
  },
);
```

### Add media to an entity

If media is enabled, you can upload media directly or associate it with an entity. E.g. you may want to upload a cover image for a post, but also a gallery of images. Since a relation to the media entity is polymorphic, you have to:
1. add a virtual field to your entity (single `medium` or multiple `media`)
2. add the relation from the owning entity to the media entity
3. specify the mapped field name by using the `mappedBy` option

```typescript
import { em, entity, text, number, systemEntity, medium, media } from "bknd";

const schema = em(
  {
    posts: entity("posts", {
      title: text().required(),
      slug: text().required(),
      content: text(),
      views: number(),
      // [!code highlight]
      // `medium` represents a single media item
      cover: medium(), // [!code highlight]
      // [!code highlight]
      // `media` represents a list of media items
      gallery: media(), // [!code highlight]
    }),
    comments: entity("comments", {
      content: text(),
    }),
    // [!code highlight]
    // add the `media` entity 
    media: systemEntity("media", { // [!code highlight]
      // [!code highlight]
      // optionally add additional fields
    }) // [!code highlight]
  },
  // now you have access to the system entity "media"
  ({ relation, index }, { posts, comments, media }) => {
    // add the `cover` relation
    relation(posts).polyToOne(media, { mappedBy: "cover" }); // [!code highlight]
    // add the `gallery` relation
    relation(posts).polyToMany(media, { mappedBy: "gallery" }); // [!code highlight]
  },
);
```


### Type completion

To get type completion, there are two options:

1. Use the CLI to [generate the types](/usage/cli#generating-types-types) (recommended)
2. If you have an initial structure created with the prototype functions, you can extend the `DB` interface with your own schema.

All entity related functions use the types defined in `DB` from `bknd`. To get type completion, you can extend that interface with your own schema:

```typescript
import { em } from "bknd";
import { Api } from "bknd/client";

const schema = em({ /* ... */ });

type Database = (typeof schema)["DB"];
declare module "bknd" {
  interface DB extends Database {}
}

const api = new Api({ /* ... */ });
const { data: posts } = await api.data.readMany("posts", {});
// `posts` is now typed as Database["posts"]
```

The type completion is available for the API as well as all provided [React hooks](/usage/react).

### Seeding the database

To seed your database with initial data, you can pass a `seed` function to the configuration. It
provides the `ModuleBuildContext` as the first argument.


```typescript
import { createApp, type ModuleBuildContext } from "bknd";

const app = createApp({
  connection: { /* ... */ },
  config: { /* ... */ },
  options: {
    seed: async (ctx: ModuleBuildContext) => {
      await ctx.em.mutator("posts").insertMany([
        { title: "First post", slug: "first-post", content: "..." },
        { title: "Second post", slug: "second-post" },
      ]);
    },
  },
});
```

Note that in [`db` mode](/usage/introduction#ui-only-mode), the seed function will only be executed on app's first boot. If a configuration already exists in the database, it will not be executed.

In [`code` mode](/usage/introduction#code-only-mode), the seed function will not be automatically executed. You can manually execute it by running the following command:

```bash
npx bknd sync --seed --force
```

See the [sync command](/usage/cli#syncing-the-database-sync) documentation for more details.
