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/*

SQL Schema migration tool for Go.

Key features:

	* Usable as a CLI tool or as a library
	* Supports SQLite, PostgreSQL, MySQL, MSSQL and Oracle databases (through gorp)
	* Can embed migrations into your application
	* Migrations are defined with SQL for full flexibility
	* Atomic migrations
	* Up/down migrations to allow rollback
	* Supports multiple database types in one project

Installation

To install the library and command line program, use the following:

	go get -v github.com/rubenv/sql-migrate/...

Command-line tool

The main command is called sql-migrate.

	$ sql-migrate --help
	usage: sql-migrate [--version] [--help] <command> [<args>]

	Available commands are:
		down      Undo a database migration
		new       Create a new migration
		redo      Reapply the last migration
		status    Show migration status
		up        Migrates the database to the most recent version available

Each command requires a configuration file (which defaults to dbconfig.yml, but can be specified with the -config flag). This config file should specify one or more environments:

	development:
		dialect: sqlite3
		datasource: test.db
		dir: migrations/sqlite3

	production:
		dialect: postgres
		datasource: dbname=myapp sslmode=disable
		dir: migrations/postgres
		table: migrations

The `table` setting is optional and will default to `gorp_migrations`.

The environment that will be used can be specified with the -env flag (defaults to development).

Use the --help flag in combination with any of the commands to get an overview of its usage:

	$ sql-migrate up --help
	Usage: sql-migrate up [options] ...

	  Migrates the database to the most recent version available.

	Options:

	  -config=config.yml   Configuration file to use.
	  -env="development"   Environment.
	  -limit=0             Limit the number of migrations (0 = unlimited).
	  -dryrun              Don't apply migrations, just print them.

The up command applies all available migrations. By contrast, down will only apply one migration by default. This behavior can be changed for both by using the -limit parameter.

The redo command will unapply the last migration and reapply it. This is useful during development, when you're writing migrations.

Use the status command to see the state of the applied migrations:

	$ sql-migrate status
	+---------------+-----------------------------------------+
	|   MIGRATION   |                 APPLIED                 |
	+---------------+-----------------------------------------+
	| 1_initial.sql | 2014-09-13 08:19:06.788354925 +0000 UTC |
	| 2_record.sql  | no                                      |
	+---------------+-----------------------------------------+

MySQL Caveat

If you are using MySQL, you must append ?parseTime=true to the datasource configuration. For example:

	production:
		dialect: mysql
		datasource: root@/dbname?parseTime=true
		dir: migrations/mysql
		table: migrations

See https://github.com/go-sql-driver/mysql#parsetime for more information.

Library

Import sql-migrate into your application:

	import "github.com/rubenv/sql-migrate"

Set up a source of migrations, this can be from memory, from a set of files or from bindata (more on that later):

	// Hardcoded strings in memory:
	migrations := &migrate.MemoryMigrationSource{
		Migrations: []*migrate.Migration{
			&migrate.Migration{
				Id:   "123",
				Up:   []string{"CREATE TABLE people (id int)"},
				Down: []string{"DROP TABLE people"},
			},
		},
	}

	// OR: Read migrations from a folder:
	migrations := &migrate.FileMigrationSource{
		Dir: "db/migrations",
	}

	// OR: Use migrations from bindata:
	migrations := &migrate.AssetMigrationSource{
		Asset:    Asset,
		AssetDir: AssetDir,
		Dir:      "migrations",
	}

Then use the Exec function to upgrade your database:

	db, err := sql.Open("sqlite3", filename)
	if err != nil {
		// Handle errors!
	}

	n, err := migrate.Exec(db, "sqlite3", migrations, migrate.Up)
	if err != nil {
		// Handle errors!
	}
	fmt.Printf("Applied %d migrations!\n", n)

Note that n can be greater than 0 even if there is an error: any migration that succeeded will remain applied even if a later one fails.

The full set of capabilities can be found in the API docs below.

Writing migrations

Migrations are defined in SQL files, which contain a set of SQL statements. Special comments are used to distinguish up and down migrations.

	-- +migrate Up
	-- SQL in section 'Up' is executed when this migration is applied
	CREATE TABLE people (id int);


	-- +migrate Down
	-- SQL section 'Down' is executed when this migration is rolled back
	DROP TABLE people;

You can put multiple statements in each block, as long as you end them with a semicolon (;).

If you have complex statements which contain semicolons, use StatementBegin and StatementEnd to indicate boundaries:

	-- +migrate Up
	CREATE TABLE people (id int);

	-- +migrate StatementBegin
	CREATE OR REPLACE FUNCTION do_something()
	returns void AS $$
	DECLARE
	  create_query text;
	BEGIN
	  -- Do something here
	END;
	$$
	language plpgsql;
	-- +migrate StatementEnd

	-- +migrate Down
	DROP FUNCTION do_something();
	DROP TABLE people;

The order in which migrations are applied is defined through the filename: sql-migrate will sort migrations based on their name. It's recommended to use an increasing version number or a timestamp as the first part of the filename.

Normally each migration is run within a transaction in order to guarantee that it is fully atomic. However some SQL commands (for example creating an index concurrently in PostgreSQL) cannot be executed inside a transaction. In order to execute such a command in a migration, the migration can be run using the notransaction option:

	-- +migrate Up notransaction
	CREATE UNIQUE INDEX people_unique_id_idx CONCURRENTLY ON people (id);

	-- +migrate Down
	DROP INDEX people_unique_id_idx;

Embedding migrations with packr

If you like your Go applications self-contained (that is: a single binary): use packr (https://github.com/gobuffalo/packr) to embed the migration files.

Just write your migration files as usual, as a set of SQL files in a folder.

Use the PackrMigrationSource in your application to find the migrations:

	migrations := &migrate.PackrMigrationSource{
		Box: packr.NewBox("./migrations"),
	}

If you already have a box and would like to use a subdirectory:

	migrations := &migrate.PackrMigrationSource{
		Box: myBox,
		Dir: "./migrations",
	}

Embedding migrations with bindata

As an alternative, but slightly less maintained, you can use bindata (https://github.com/shuLhan/go-bindata) to embed the migration files.

Just write your migration files as usual, as a set of SQL files in a folder.

Then use bindata to generate a .go file with the migrations embedded:

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

The resulting bindata.go file will contain your migrations. Remember to regenerate your bindata.go file whenever you add/modify a migration (go generate will help here, once it arrives).

Use the AssetMigrationSource in your application to find the migrations:

	migrations := &migrate.AssetMigrationSource{
		Asset:    Asset,
		AssetDir: AssetDir,
		Dir:      "db/migrations",
	}

Both Asset and AssetDir are functions provided by bindata.

Then proceed as usual.

Extending

Adding a new migration source means implementing MigrationSource.

	type MigrationSource interface {
		FindMigrations() ([]*Migration, error)
	}

The resulting slice of migrations will be executed in the given order, so it should usually be sorted by the Id field.
*/
package migrate