I’m performing migration from Drupal 9 into another Drupal 9 project. Let’s say "content features" migration.

In a node migration I’m trying to create stubs for media items.

The media source has two id keys: mid, langcode. The mid key is getting from field’s target_id property. But there is no language property on field’s level and I’m trying to pass node’s language as second id value for the media lookup.

The migrate_lookup plugin tries to find media entity by mid and langcode properties: MigrationLookup::transform():

if (isset($this->configuration['source_ids'][$lookup_migration_id])) {   $lookup_value = array_values($row->getMultiple($this->configuration['source_ids'][$lookup_migration_id])); } 

then getMultiple() tries to get values from the current iteration.

Does someone know how to pass root row instead of iteration row?

... process:   langcode: langcode   ...    field_cover_image:     - plugin: sub_process       source: field_cover_image       process:         lang:           plugin: default_value           default_value: 'en'         target_id:           plugin: migration_lookup           source: target_id           migration: migrate_media_image           source_ids:             migrate_media_image:               - target_id               - ROOT_ROW_SOURCE_PROPERTY_LANGCODE 

I wonder also if it possible to use constants within sub_process and $row->getMultiple()?

An example:

...       process:         target_id:           plugin: migration_lookup           source: target_id           migration: migrate_media_image           source_ids:             migrate_media_image:               - target_id               - constants/default_language