Database Migrations

Nova provides a simple, file-based database migration tool accessible directly through the nova command-line binary. It allows you to manage database schema changes using plain SQL files stored in a dedicated folder, driven by simple commands.

CLI Driven: Manage migrations using nova migrate <action>.
Plain SQL: Write standard SQL for your target database.
Version Tracking: Automatically tracks the applied migration version in a dedicated schema table.
Up/Down Migrations: Each migration file contains SQL for both applying (up) and reverting (down) the change.
Timestamp-Based Ordering: Migration files are ordered based on a timestamp prefix in their filename.
Step Control: Apply or roll back all pending migrations or a specific number of steps via command arguments.
Environment Configuration: Reads database connection details from the DATABASE_URL environment variable (supports .env files).
Driver Detection: Automatically detects the database driver (postgres, mysql, sqlite) based on the DATABASE_URL prefix.
Low dependencies: Relies only on the Go standard library and database drivers for Postgres, MySQL/MariaDB and SQLite.

Getting Started
Configuration (DATABASE_URL)
Core Concepts
CLI Commands
Programmatic Usage (Advanced)

Getting Started

Set DATABASE_URL: Ensure the DATABASE_URL environment variable is set correctly for your target database. You can also place it in a .env file in the directory where you run nova.

# Example for PostgreSQL
export DATABASE_URL="postgres://user:password@host:port/dbname?sslmode=disable"

# Example for SQLite
export DATABASE_URL="file:./my_app_data.db"

Create the migrations Folder: In the root of your project (or where you run nova), create the folder:
```
mkdir migrations
```

Create Your First Migration: Use the new command:

nova migrate new create_users_table
# Output: Created new migration: migrations/1678886400_create_users_table.sql (timestamp will vary)

Edit the SQL File: Open the generated .sql file and add your SQL statements under the appropriate delimiters:

-- migrations/1678886400_create_users_table.sql

-- migrate:up
CREATE TABLE users (
    id SERIAL PRIMARY KEY,
    username VARCHAR(50) UNIQUE NOT NULL,
    created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP
);

-- migrate:down
DROP TABLE IF EXISTS users;

Apply the Migration: Use the up command:

nova migrate up
# Output: Applied migration migrations/1678886400_create_users_table.sql
# Output: Successfully applied 1 migration(s).

Your database schema is now updated!

Configuration (`DATABASE_URL`)

The nova migrate command requires the DATABASE_URL environment variable to connect to your database.

Format: Use a standard DSN (Data Source Name) URL format.
Supported Drivers (Auto-Detected):
- PostgreSQL (postgres://...)
- MySQL (mysql://...)
- SQLite (file:... or path ending in .db)
.env File: If a .env file exists in the current directory, nova migrate will attempt to load environment variables from it. Variables already present in the environment take precedence.

Core Concepts

These concepts explain how the migration files and tracking work.

The `migrations` Folder

Must be named migrations.
Must exist in the directory where you execute the nova migrate command or call the programmatic functions.
Contains all your .sql migration files.

Migration File Naming

Format: <version>_<descriptive_name>.sql
<version>: An integer, typically a Unix timestamp (e.g., 1678886400), used for ordering. Generated automatically by nova migrate new.
<descriptive_name>: Briefly explains the migration’s purpose (e.g., create_users_table).

Migration File Structure

Plain SQL file (.sql).
Must contain -- migrate:up and -- migrate:down delimiters.
SQL statements under -- migrate:up are executed by nova migrate up.
SQL statements under -- migrate:down are executed by nova migrate down.

-- migrations/TIMESTAMP_add_email_to_users.sql

-- migrate:up
ALTER TABLE users ADD COLUMN email VARCHAR(255) UNIQUE;
CREATE INDEX idx_users_email ON users(email);

-- migrate:down
DROP INDEX IF EXISTS idx_users_email;
ALTER TABLE users DROP COLUMN IF EXISTS email;

Version Tracking (`schema_version` table)

The first time nova migrate up or nova migrate down runs (either via CLI or programmatically), it automatically creates a table named schema_version in your database.
This table stores the <version> number of the most recently applied migration.
The migration commands use this table to determine which migrations need to be applied or rolled back.

CLI Commands

Manage your database schema using these subcommands of nova migrate.

`nova migrate new`

Creates a new migration file skeleton.

Syntax: nova migrate new <migration_name>
Arguments:
- <migration_name> (Required): A descriptive name for the migration (e.g., add_indexes_to_orders). Use underscores for spaces.
Behavior:
- Creates the migrations folder if needed.
- Generates a filename: <timestamp>_<migration_name>.sql.
- Writes the basic -- migrate:up and -- migrate:down template into the file.

Example:

nova migrate new add_last_login_to_users
# Creates migrations/1678886402_add_last_login_to_users.sql (example)

`nova migrate up`

Applies pending migrations to the database.

Syntax: nova migrate up [steps]
Arguments:
- [steps] (Optional): An integer specifying the maximum number of migrations to apply. If omitted or 0, applies all pending migrations.
Behavior:
- Connects to the database using DATABASE_URL.
- Reads the current version from the schema_version table.
- Finds all .sql files in the migrations folder with a version greater than the current version.
- Sorts these pending migrations chronologically.
- Executes the SQL statements under -- migrate:up for each pending migration, up to the specified [steps] limit.
- Updates the schema_version table after each successful migration file application.
- Prints status messages.

Examples:

# Apply all pending migrations
nova migrate up

# Apply only the next 2 pending migrations
nova migrate up 2

`nova migrate down`

Rolls back previously applied migrations.

Syntax: nova migrate down [steps]
Arguments:
- [steps] (Optional): An integer specifying the exact number of migrations to roll back. If omitted or 0, defaults to rolling back one migration.
Behavior:
- Connects to the database using DATABASE_URL.
- Reads the current version from the schema_version table.
- Finds all .sql files in the migrations folder with a version less than or equal to the current version.
- Sorts these applied migrations in reverse chronological order.
- Executes the SQL statements under -- migrate:down for the most recent applied migrations, up to the specified number of [steps].
- Updates the schema_version table after each successful rollback to reflect the new latest version.
- Prints status messages.

Examples:

# Roll back the single most recent migration
nova migrate down
# OR
nova migrate down 1

# Roll back the last 3 applied migrations
nova migrate down 3

Programmatic Usage (Advanced)

While the nova migrate CLI command is the recommended way to manage migrations, the underlying functions are exported and can be used directly within your Go code if you need more control or want to embed migration logic into your application’s startup sequence or custom tooling.

Note: When using these functions programmatically, you are responsible for obtaining the *sql.DB database connection handle yourself. The functions do not read the DATABASE_URL environment variable out of the box.

`CreateNewMigration`

func CreateNewMigration(name string) error

Identical in behavior to the CLI’s new action, but called from Go code.

Parameters:
- name (string): Descriptive name for the migration.
Returns: An error if file creation fails, otherwise nil.

Usage:

import "github.com/xlc-dev/nova/nova"

// ... inside your Go code ...
err := nova.CreateNewMigration("seed_initial_data")
if err != nil {
    log.Printf("Failed to create migration file: %v", err)
    // Handle error appropriately
}

`MigrateUp`

func MigrateUp(db *sql.DB, steps int) error

Identical in behavior to the CLI’s up action, but called from Go code.

Parameters:
- db (*sql.DB): An active database connection handle obtained via sql.Open.
- steps (int): Max number of migrations to apply (0 = all).
Returns: An error if any migration step fails, otherwise nil.

Usage:

import (
    "database/sql"

	_ "github.com/lib/pq" // Import your DB driver
    "github.com/xlc-dev/nova/nova"
)

// ... inside your Go code ...
db, err := sql.Open("postgres", "your_connection_string")
if err != nil { /* handle error */ }
defer db.Close()

log.Println("Applying database migrations...")
// Apply all pending migrations during application startup
err = nova.MigrateUp(db, 0)
if err != nil {
    log.Fatalf("Database migration failed: %v", err) // Critical error on startup
}
log.Println("Database migrations applied successfully.")

`MigrateDown`

func MigrateDown(db *sql.DB, steps int) error

Identical in behavior to the CLI’s down action, but called from Go code.

Parameters:
- db (*sql.DB): An active database connection handle.
- steps (int): Number of migrations to roll back (0 or negative = 1).
Returns: An error if any rollback step fails, otherwise nil.

Usage:

import (
    "database/sql"

	_ "github.com/lib/pq" // Import your DB driver
    "github.com/xlc-dev/nova/nova"
)

// ... inside custom tooling or specific Go code ...
db, err := sql.Open("postgres", "your_connection_string")
if err != nil { /* handle error */ }
defer db.Close()

log.Println("Rolling back the last migration...")
// Roll back one migration
err = nova.MigrateDown(db, 1)
if err != nil {
    log.Printf("Rollback failed: %v", err)
    // Handle error appropriately
} else {
    log.Println("Rollback successful.")
}

Important: When using these functions programmatically, the status messages (Applied migration..., Rolled back migration...) are still printed to standard output. You might want to capture/redirect stdout if integrating into a larger system where this output is undesirable.