Tutorial

In this tutorial, we'll guide you through the basics of using Bolt by running through how you can create a migration, apply it, revert it, and see the status of your migrations.

Prerequisites

Before starting this tutorial, make sure you have:

• Bolt installed (see Installation)
• Docker installed (for running the database container)

Creating your first migration

Run the following command to create your first migration:

bolt new -m "my first migration"

Output:

Created migration 20240316145038 - my first migration.

Upon completion, a migrations directory will be created with the following structure:

migrations
└── 20240316145038_my_first_migration.sql

1 directory, 1 file

Bolt automatically creates the migrations directory and your migration scripts inside it.

Writing your migration scripts

Bolt utilizes plain SQL for migration scripts. Each migration file contains a comment for the upgrade script portion with -- migrate:up and a comment for the downgrade script with -- migrate:down.

1. Open up 20240316145038_my_first_migration.sql

You'll see the following template in the file for your migration:

-- migrate:up

-- migrate:down

1. Write your migration script

-- migrate:up
CREATE TABLE users (
    id SERIAL PRIMARY KEY,
    name VARCHAR(255) NOT NULL,
    email VARCHAR(255) NOT NULL,
    created_at TIMESTAMP NOT NULL DEFAULT NOW(),
    updated_at TIMESTAMP NOT NULL DEFAULT NOW()
);

-- migrate:down
DROP TABLE users;

Starting up a Database Container

We'll use Docker to run a PostgreSQL database container for this tutorial:

1. Install Docker

If you don't have docker installed, view the installation instructions here.

1. Startup the PostgreSQL container

docker run \
  --name bolt-postgres \
  --env POSTGRES_USER=bolt_user \
  --env POSTGRES_PASSWORD=bolt_password \
  --env POSTGRES_DB=bolt_tutorial_db \
  --publish 5432:5432 \
  --detach \
  postgres:latest

Configuring Bolt

Bolt can be configured with a bolt.toml file and environment variables. For simplicity, we'll use a bolt.toml file in this tutorial.

1. Create a bolt.toml file:

touch bolt.toml

1. Add the following contents to the file:

[database]
dsn = "postgresql://bolt_user:bolt_password@localhost:5432/bolt_tutorial_db?sslmode=disable"
driver = "postgresql"

Applying your migration

Apply your migration, which will execute the upgrade script:

bolt up

Output:

Applying migration 20240316145038_my_first_migration..
Successfully applied migration 20240316145038_my_first_migration in 3.217875ms!

Checking Migration Status

To view the status of your migration:

bolt status

Output:

Version           Message               Applied
20240316145038    my_first_migration    X

This command displays the migration's version, name, and whether the migration was applied or not.

Verifying the Migration

Connect to the database container to confirm the users table was created:

docker exec -it bolt-postgres psql -U bolt_user -d bolt_tutorial_db

bolt_tutorial_db=# \dt
              List of relations
 Schema |      Name       | Type  |   Owner
--------+-----------------+-------+-----------
 public | bolt_migrations | table | bolt_user
 public | users           | table | bolt_user
(2 rows)

We can see that our users table was created successfully. We also see another table that we didn't explicitly create called bolt_migrations. This table is used by Bolt to keep track of which migrations have been applied to your database. Generally, you should not modify this table manually.

Downgrading Your Migration

To revert your migration:

bolt down

Output:

Reverting migration 20240316145038_my_first_migration..
Successfully reverted migration 20240316145038_my_first_migration in 6.283667ms!

Verifying Migration Reversion

Reconnect to the database container and check that the users table has been removed:

docker exec -it bolt-postgres psql -U bolt_user -d bolt_tutorial_db

bolt_tutorial_db=# \dt
              List of relations
 Schema |      Name       | Type  |   Owner
--------+-----------------+-------+-----------
 public | bolt_migrations | table | bolt_user
(1 row)

Creating a migration with dependencies

Let's create another migration that depends on the first one:

bolt new -m "create posts table"

Open the new migration file. You'll see that Bolt automatically added a dependency on the previous migration:

-- depends: 20240316145038
-- migrate:up

-- migrate:down

Add the migration SQL:

-- depends: 20240316145038
-- migrate:up
CREATE TABLE posts (
    id SERIAL PRIMARY KEY,
    user_id INTEGER NOT NULL REFERENCES users(id),
    title VARCHAR(255) NOT NULL,
    content TEXT NOT NULL,
    created_at TIMESTAMP NOT NULL DEFAULT NOW()
);

-- migrate:down
DROP TABLE posts;

Apply the new migration:

bolt up

The dependency ensures that the users table exists before creating the posts table with its foreign key reference.

Next Steps

Congratulations! You've learned the core features of Bolt.

To learn more:

• Check out How-To Guides for specific tasks
• Browse the Reference for detailed command and configuration documentation
• Read the Explanation section to understand how Bolt works internally