Migration

Simple and pragmatic migrations for Go applications.

Features

• Super simple driver interface to allow easy implementation for more database/migration drivers.
• Embeddable migration files.
• Support for up/down migrations.
• Atomic migrations (where possible, depending on database support).
• Support for using Go code as migrations

Drivers

• Apache Phoenix
• Golang (runs generic go functions)
• MySQL
• PostgreSQL
• SQLite

Quickstart

// Create migration source
assetMigration := &migration.AssetMigrationSource{
    Asset:    Asset,
    AssetDir: AssetDir,
    Dir:      "test-migrations",
}

// Create driver
driver, err := phoenix.New("http://localhost:8765")

// Run all up migrations
applied, err := Migrate(driver, assetMigration, migration.Up, 0)

// Remove the last 2 migrations
applied, err := Migrate(driver, assetMigration, migration.Down, 2)

Writing migrations

Migrations are extremely simple to write:

• Separate your up and down migrations into different files. For example, 1_init.up.sql and 1_init.down.sql.
• Prefix your migration with a number or timestamp for versioning: 1_init.up.sql or 1475813115_init.up.sql.
• The file-extension can be anything you want, but must be present. For example, 1_init.up.sql is valid, but 1_init.up is not,

Let's say we want to write our first migration to initialize the database.

In that case, we would have a file called 1_init.up.sql containing SQL statements for the up migration:

CREATE TABLE test_data (
  id BIGINT NOT NULL PRIMARY KEY,
)

We also create a 1_init.down.sql file containing SQL statements for the down migration:

DROP TABLE IF EXISTS test_data

Embedding migration files

We use go-bindata to embed migration files. In the simpliest case, assuming your migration files are in migrations/, just run:

go-bindata -o bindata.go -pkg myapp migrations/

Then, use AssetMigrationSource to find the migrations:

assetMigration := &migration.AssetMigrationSource{
    Asset:    Asset,
    AssetDir: AssetDir,
    Dir:      "test-migrations",
}

The Asset and AssetDir functions are generated by go-bindata.

Using Go for migrations

Sometimes, we might be working with a database or have a situation where the query language is not expressive enough to perform the required migrations. For example, we might have to get some data out of the database, perform some transformations and then write it back. For these type of situations, you can use Go for migrations.

When using Go for migrations, create a golang.Source using golang.NewSource(). Then, simply add migrations to the source using the AddMigration() method. You will need to pass in the name of the migration without the extension and direction, e.g. 1_init. For the second parameter, pass in the direction (migration.Up or migration.Down) and for the third parameter, pass in a function or method with this signature: func(c *golangConfig) error for running the migration.

If your migrations need to access configuration values or database clients, create a golang.Config struct using golang.NewConfig(). This is concurrency-safe, and you can set values into it using Set() and retrieve values using Get().

Finally, you need to define 2 functions:

• A function for writing or deleting an applied migration matching this signature: func(config *golang.Config, id string, direction migration.Direction) error
• A function for getting a list of applied migrations matching this signature: func(config *golang.Config) ([]string, error)

These are required for initializing the driver:

driver, err := golang.New(source, updateVersion, applied, config)

Here's a quick example:

source := golang.NewSource()

source.AddMigration("1_init", migration.Up, func(c *golang.Config) error {
    // Run up migration here
    
    // If required, you can retrieve configuration here: something := c.Get("something")
})

source.AddMigration("1_init", migration.Down, func(c *golang.Config) error {
    // Run down migration here
})

// Create config
config := golang.NewConfig()
config.Set("test", "test")

// Define functions
applied := func(c *golang.Config) ([]string, error) {
    // Return list of applied migrations
}

updateVersion := func(id string, direction migration.Direction, c *golangC.onfig) error {
    // Write or delete applied migration in storage
}

// Create driver
driver, err := golang.New(source, updateVersion, applied, config)

// Run migrations
count, err = migration.Migrate(driver, source, migration.Up, 0)

TODO (Pull requests welcomed!)

• Command line program to run migrations
• MigrationSource that uses migrations from the local file system
• More drivers

Why yet another migration library?

We wanted a migration library with the following features:

• Open to extension for all sorts of databases, not just database/sql drivers or an ORM.
• Easily embeddable in a Go application.
• Support for embedding migration files directly into the app.

We narrowed our focus down to 2 contenders: sql-migrate and migrate

sql-migrate leans heavily on the gorp ORM library to perform migrations. Unfortunately, this means that we were restricted to databases supported by gorp. It is easily embeddable in a Go app and supports embedding migration files directly into the Go binary. If database support was a bit more flexible, we would have gone with it.

migrate is highly extensible, and adding support for another database is extremely trivial. However, due to it using the scheme in the dsn to determine which database driver to use, it prevented us from easily implementing an Apache Phoenix driver, which uses the scheme to determine if we should connect over http or https. Due to the way the project is structured, it was also almost impossible to add support for embeddable migration files without major changes.

License

This library is licensed under the Apache 2 License.