Migrations

Migrations change the database schema and operate in three steps:

Pre schema changes
Schema changes
Post schema changes

Apps can have multiple migrations, which allows a way more flexible updating process. For example, you can rename a column while copying all the content with 3 steps packed in 2 migrations.

The Nextcloud updater logic will look for your migration files in the apps lib/Migration folder.

Note

While in theory you can run any code in the pre- and post-steps, we recommend not to use actual php classes. With migrations you can update from any old version to any new version as long as the migration steps are retained. Since they are also used for installation, you should keep them anyway. But this also means when you change a php class which you use in your migration, the code may be executed on different database/file/code standings when being ran in an upgrade situation.

Note

Since Nextcloud stores, which migrations have been executed already you must not “update” migrations. The recommendation is to keep them untouched as long as possible. You should only adjust it to make sure it still executes, but additional changes to the database should be done in a new migration.

1. Migration 1: Schema change

With this step the new column gets created:

public function changeSchema(IOutput $output, \Closure $schemaClosure, array $options) {
           /** @var ISchemaWrapper $schema */
           $schema = $schemaClosure();

           $table = $schema->getTable('twofactor_backupcodes');

           $table->addColumn('user_id', \OCP\DB\Types::STRING, [
                   'notnull' => true,
                   'length' => 64,
           ]);

           return $schema;
  }

2. Migration 1: Post schema change

In this step the content gets copied from the old to the new column.

Note

This could also be done as part of the second migration as part of a pre schema change

public function postSchemaChange(IOutput $output, \Closure $schemaClosure, array $options) {
       $query = $this->db->getQueryBuilder();
       $query->update('twofactor_backupcodes')
               ->set('user_id', 'uid');
       $query->executeStatement();
}

3. Migration 2: Schema change

With this the old column gets removed.

 public function changeSchema(IOutput $output, \Closure $schemaClosure, array $options) {
        /** @var ISchemaWrapper $schema */
        $schema = $schemaClosure();

        $table = $schema->getTable('twofactor_backupcodes');
        $table->dropColumn('uid');

        return $schema;
}

Construction of migration classes

All migration classes are constructed via Basic Pattern of Dependency Injection. So if your migration steps need additional dependencies, these can be defined in the constructor of your migration class.

Example: If your migration needs to execute SQL statements, inject a OCP\IDBConnection instance into your migration class like this:

class Version2404Date20220903071748 extends SimpleMigrationStep {
   public function __construct(
      private IDBConnection $db
   ) {
   }

   public function postSchemaChange(IOutput $output, \Closure $schemaClosure, array $options) {
      $query = $this->db->getQueryBuilder();
      // execute some SQL ...
   }
}

Migrations and Metadata

Since 30, details about migrations are available to administrator as metadata can be attached to your migration class by adding specific PHP Attributes:

use OCP\Migration\Attributes\CreateTable;
use OCP\Migration\Attributes\ColumnType;
use OCP\Migration\Attributes\ModifyColumn;

#[CreateTable(
    table: 'new_table',
    description: 'Table is used to store things, but also to get more things',
    notes: ['this is a notice', 'and another one, if really needed']
)]
#[ModifyColumn(table: 'other_table', name: 'this_field', type: ColumnType::BIGINT)]
class Version30000Date20240729185117 extends SimpleMigrationStep {
    public function changeSchema(IOutput $output, Closure $schemaClosure, array $options) {
[...]
    }
}

List of available Migration Attributes:

\OCP\Migration\Attributes\AddColumn if your migration implies the creation of a new column
\OCP\Migration\Attributes\AddIndex if your migration adds a new index
\OCP\Migration\Attributes\CreateTable if your migration creates a new table
\OCP\Migration\Attributes\DropColumn if your migration drops a column
\OCP\Migration\Attributes\DropIndex if your migration drops an index
\OCP\Migration\Attributes\DropTable if your migration drops a table
\OCP\Migration\Attributes\ModifyColumn if your migration modifies a column

Console commands

The following occ commands help you create and manage migrations:

migrations
 migrations:execute  execute a single migration version manually
 migrations:generate generate a new migration file for an app
 migrations:migrate  execute migrations to a specified or the latest version
 migrations:preview  preview available DB migrations before an upgrade
 migrations:status   view the status of migrations for an app

migrations:execute

Execute a single migration version manually. The version argument is the migration class name without the Version prefix — for example, if your migration is named Version2404Date20220903071748, the version is 2404Date20220903071748:

sudo -E -u www-data php occ migrations:execute myapp 2404Date20220903071748

Note

Without debug mode enabled, migrations:execute will refuse to run a version that has already been executed or that would roll back a previous migration. Enable debug mode (’debug’ => true in config.php) to override this restriction during development.

migrations:generate

Generate a new migration file for an app. The version argument is the major version of your app as an integer. Use the major and minor digits of your app version, mapped to 3 digits (1.0.x => 1000, 2.34.x => 2034), to leave room for parallel branch migrations:

sudo -E -u www-data php occ migrations:generate myapp 1000

The generated file is placed in apps/myapp/lib/Migration/.

Note

After generating a migration you may need to run composer dump-autoload before it can be executed.

migrations:migrate

Execute all pending migrations for an app, or migrate to a specific version. Accepts a version number (YYYYMMDDHHMMSS) or an alias (first, prev, next, latest):

sudo -E -u www-data php occ migrations:migrate myapp
sudo -E -u www-data php occ migrations:migrate myapp prev

migrations:preview

Preview the DB migrations that would be applied during an upgrade to a given version, without executing them:

sudo -E -u www-data php occ migrations:preview 30.0.0

migrations:status

Show which migrations have been executed and which are pending for an app:

sudo -E -u www-data php occ migrations:status myapp

Adding indices

Adding indices to existing tables can take long time, especially on large tables. Therefore it is recommended to not add the indices in the migration itself, but to indicate the index requirement to the server by adding a listener for the AddMissingIndicesEvent. This way the migration can be executed in a separate step and do not block the upgrade process. For new installations the index should still be added to the migration that creates the table.

class AddMissingIndicesListener implements IEventListener {
   public function handle(Event $event): void {
      if (!$event instanceof AddMissingIndicesEvent) {
         return;
      }

      $event->addMissingIndex('my_table', 'my_index', ['column_a', 'column_b']);
   }
}

Replacing indices

Added in version 29.0.0.

Similar to adding an index to an existing table, it could be necessary to replace one or more indices with a new one. To avoid a gap between dropping the old indices in a migration and adding the new one through AddMissingIndicesEvent, it is possible to do both at once in AddMissingIndicesEvent.

If none of the previous indices are found, e.g. because they were optional and not created yet, the replacement index will be treated as missing index.

Note

Make sure to not use the same index name for the new index as for old indices.

class ReplaceIndicesListener implements IEventListener {
   public function handle(Event $event): void {
      if (!$event instanceof AddMissingIndicesEvent) {
         return;
      }

      $event->replaceIndex('my_table', ['my_old_index_one', 'my_old_index_two'], 'my_new_index', ['column_a', 'column_b'], false);
   }
}