Clear offers a migration system. Migration allow you to handle state update of your database.
Migration is a list of change going through a direction, up (commit changes) or down (rollback changes).
In clear, a migration is defined like this:
class MyMigration1include Clear::Migrationdef change(direction)direction.up do#do something on commitenddirection.down do#do something on rollbackendendend
The basic usage is to execute your own SQL (e.g. CREATE TABLE, ALTER, GRANT etc...).
To do it, just call
execute into your direction block.
class MyMigration1include Clear::Migrationdef change(direction)direction.up doexecute("CREATE TABLE my_models...")enddirection.down doexecute("DROP TABLE my_models")endendend
Clear offers helpers for simplify declaring your migration
Clear provides DSL looking like ActiveRecord for creating a table.
create_table(:users) do |t|t.column :first_name, :string, index: truet.column :last_name, :string, unique: true# Will create a "user_info_id" field of type longint with a foreign key constraint# This reference can be null, and if the user_info is deleted then the user is deleted too.t.references to: "user_infos", name: "user_info_id", on_delete: "cascade", null: true# Example of creating index on full namet.index "lower(first_name || ' ' || last_name)", using: :btreet.timestampsend
Migration should be ordered by a number. This number can be written in different way:
In case of mixing multiple classes into the same file, you can append the number at the end of the class name:
class Migration1include Clear::Migrationdef change(dir)#...endend
If you're using one file per migration, you can prepend the ordering number at the start of the file name:
Finally, if you feel more rock'n'roll and build a complex dynamic migration system on top of Clear, you can override the uid method:
class Migration1include Clear::Migrationdef uid123_i64 #Number must be a signed 64bits integer !enddef change(dir)#...endend
Clear will offers soon a CLI; meanwhile, you can call migration update using methods in the Migration Manager:
# Activate all the migrations. Will call change with up direction for each down migrationsClear::Migration::Manager.instance.apply_all
# Go to a specific migration. All migration with a number above than the version number will be downed if not yet down.# All migrations with a version number below will be activated if not yet up.Clear::Migration::Manager.instance.apply_to(version_number)