Add a farm_migrate:rollback Drush command that rolls back all farmOS migrations.

docs/hosting/migration.md

@@ -75,6 +75,28 @@ known issues.
 
 Please open bug reports in the farmOS issue queue if new issues are discovered.
 
+## Rolling back migration
+
+Migrations can be rolled back with the following command:
+
+    drush farm_migrate:rollback
+
+Alternatively, migration groups can be rolled back individually. This should be
+done in the following order (reverse of the order of import):
+
+    drush migrate:import --group=farm_migrate_plan
+    drush migrate:import --group=farm_migrate_log
+    drush migrate:import --group=farm_migrate_quantity
+    drush migrate:import --group=farm_migrate_sensor_data
+    drush migrate:import --group=farm_migrate_asset_parent
+    drush migrate:import --group=farm_migrate_area
+    drush migrate:import --group=farm_migrate_asset
+    drush migrate:import --group=farm_migrate_taxonomy
+    drush migrate:import --group=farm_migrate_file
+    drush migrate:import --group=farm_migrate_user
+    drush migrate:import --group=farm_migrate_role
+    drush migrate:import --group=farm_migrate_config
+
 ## Migrating files
 
 farmOS allows files to be uploaded/attached to records. In order to migrate

modules/core/migrate/src/Commands/FarmMigrateCommands.php

@@ -22,6 +22,17 @@ class FarmMigrateCommands extends MigrateToolsCommands {
     $this->executeFarmMigrations();
   }
 
+  /**
+   * Rollback a 1.x data migration.
+   *
+   * @command farm_migrate:rollback
+   *
+   * @usage farm_migrate:rollback
+   */
+  public function farmRollback() {
+    $this->executeFarmRollback();
+  }
+
   /**
    * Define the farmOS migration groups in the order they should be executed.
    *
@@ -61,4 +72,21 @@ class FarmMigrateCommands extends MigrateToolsCommands {
     }
   }
 
+  /**
+   * Rollback all farmOS migrations.
+   *
+   * @throws \Exception
+   *   If some rollbacks failed during execution.
+   */
+  protected function executeFarmRollback() {
+    $groups = $this->farmMigrationGroups();
+    $groups = array_reverse($groups);
+    foreach ($groups as $group) {
+      $options = [
+        'group' => $group,
+      ];
+      $this->rollback('', $options);
+    }
+  }
+
 }