Migrations

Now that we have defined our schema in TypeScript, we need to tell our actual database about these tables. We do this using Migrations.

Think of migrations as “version control” for your database. They track changes over time (e.g., creating a table, adding a column).

Configuration

First, we need to configure Drizzle Kit. This tool looks at your schema file and generates the necessary SQL commands.

Create a drizzle.config.ts file in your project root:

drizzle.config.ts

import { defineConfig } from "drizzle-kit";

export default defineConfig({
  out: "./drizzle", // Where to save migration files
  schema: "./src/worker/db/schema.ts", // Path to your schema
  dialect: "sqlite",
  driver: "d1-http",
});

You also need to make sure your wrangler.json is set up with a D1 database binding.

wrangler.json

{
  "d1_databases": [
    {
      "binding": "DB", // How we access it in code (env.DB)
      "database_name": "my-app-db",
      "database_id": "xxxx-xxxx-xxxx-xxxx", // Your D1 ID
      "migrations_dir": "drizzle" // Must match 'out' in drizzle.config.ts
    }
  ]
}

The Workflow

1. Generate Migrations

   Run the generate command. Drizzle Kit will compare your TypeScript schema to the existing migration files and generate a new SQL file for any changes.

   bunx drizzle-kit generate

   You will see a new file in your drizzle/ folder, something like 0000_init.sql.

2. Apply Migrations (Local)

   To apply these changes to your local development database:

   bunx wrangler d1 migrations apply my-app-db --local

3. Apply Migrations (Production)

   To apply these changes to your live production database:

   bunx wrangler d1 migrations apply my-app-db --remote

Why this is powerful

• Safety: You review the SQL before it runs.
• History: You have a record of every change made to your DB.
• Reproducibility: Anyone on your team can run the migrations and get the exact same database structure.

In the next section, we will write code to interact with this database!