How Golang DB migration tool work?

migrate

Database migrations tool is written in Go. Use as CLI or import as a library.

• Migrate reads migrations from sources and applies them in the correct order to a database.

The migration tool uses a schema_migrations table. One table exists for one DB.

mysql> select * from schema_migrations;
+---------+-------+
| version | dirty |
+---------+-------+
|      33 |     0 |
+---------+-------+
1 row in set (0.00 sec)

The command to apply all migrations to a DB would check-in schema_migrations table and pick migrations after the version (for the current case – 34 and onwards).

migration up
migration down 33

The down migration executes the down file for version 33 and updates the schema_migrations table.

Code

Migration files are read from 1..N if no version is specified.

migrate/migrate.go

// read reads either up or down migrations from source `from` to `to`.
// Each migration is then written to the ret channel.
// If an error occurs during reading, that error is written to the ret channel, too.
// Once read is done reading…