> ## Documentation Index
> Fetch the complete documentation index at: https://docs.thebay.cloud/llms.txt
> Use this file to discover all available pages before exploring further.

# Databases

> The one you did not ask for, and the one you already had.

## The dependency is the declaration

An app that imports a driver gets a database. Nothing else is required — no
config, no dashboard step, no connection string.

```js theme={null}
const { Pool } = require("pg");
const pool = new Pool({ connectionString: process.env.DATABASE_URL });
```

Ship that and the build says:

```
Provision postgres (via pg)
Provisioning Postgres…
Provisioned Postgres database xf4u7
Database isolated — this app connects as app_xf4u7 and no other app can reach it
Stored DATABASE_URL, POSTGRES_PASSWORD, PGPASSWORD… in Secret Manager
```

## Isolation

Each app connects as its own role, `app_<slug>`. No app can reach another app's
data, and this is enforced at the database rather than by convention.

## Migrations

Put them in `release`, which runs once per deploy, before any traffic:

```json theme={null}
{ "release": "npx prisma migrate deploy" }
```

<Warning>
  Never fold a migration into `start`. It re-runs on every cold start and every
  scale-out instance, concurrently.
</Warning>

## Looking at the data

```bash theme={null}
bay db <app>                                  # tables, with row counts
bay db <app> users --limit 50
bay db <app> --sql "select count(*) from users"
```

One read-only statement at a time. The CLI is for looking, not for migrating.

## Keeping the database you already have

```json theme={null}
{
  "resources": {
    "database": {
      "provider": "external",
      "engine": "postgres",
      "urlFrom": "DATABASE_URL"
    }
  }
}
```

```bash theme={null}
bay env my-app set DATABASE_URL=postgresql://...
```

`urlFrom` names a **secret**, not a URL. Bay provisions nothing, touches nothing,
and only needs to know that a value exists under that name and reached the
revision.

## Deleting an app

```bash theme={null}
bay delete <app> --yes
```

The database and the bucket are kept. The data outlives the app on purpose.